I

JOURNAL OF SHELLFISH RESEARCH

Vol. 1, No. 1 June 1981

CONTENTS

V. G. Burrell. Jr., J. J. Manzi and W. Z. Carson

Growtli and Mortality of Two Types of Seed Oysters from the Wando River, South Carolina 1

James A. Perdue, John //. Beat tie and Kenneth K. Chew

Some Relationships between Gametogenic Cycle and Summer Mortality Phenomenon

in the Pacific Oyster (Crassostrea gigas) in Washington State 9

George C Miller, Donald M. A Hen and T. J. Costello

Spawning of the Calico Scallop Argopecten gibbus in Relation to Season and Temperature 17

Douglas S. Jones

Reproductive Cycles of the Atlantic Surf Clam Spisula solidissima, and the Ocean

Quahog Arctica islandica off New Jersey 23

Michael J. Fogarty

Distribution and Relative Abundance of the Ocean Quahog Arctica islandica in

Rhode Island Sound and Off Martha's Vineyard, Massachusetts 33

Richard S. Appeldoorn

Response of Soft-shell Clam (Mya arenaria) Growth to Onset and Abatement of Pollution 41

J. L. McHugh

Recent Advances in Hard Clam Mariculture 51

Herbert Hidu, Samuel R. Chapman and David Dean

Oyster Mariculture in Subboreal (Maine, United States of America) Waters: Cultch-

less Setting and Nursery Culture of European and American Oysters 57

Scott M. Gallager and Roger Mann

Use of Lipid Specific Staining Techniques for Assaying Condition in Cultured Bivalve Larvae 69

B. B. Goldstein and O. A. Roels

Nitrogen Balance of Juvenile Southern Quahogs (Mercenaria campechiensis) at Different Feed Levels .... 75

Carolyn Brown

A Study of Two Shellfish -Pathogenic Vibrio Strains Isolated from a Long Island

Hatchery during a Recent Outbreak of Disease 83

Robert W. Elner

Diet of Green Crab Carcinus maenas (L.) from Port Hebert, Southwestern Nova Scotia 89

Stephen C Jewett

Variations in some Reproductive Aspects of Female Snow Crabs Chionoecetes opilio 95

Abstracts of Technical Papers Presented at the 1980 Annual MeetingNational Shellfisheries

Association, Hyannis, Massachusetts - June 9-12, 1980 101

Abstracts of Technical Papers Presented at the 1 980 Annual Meeting National Shellfisheries

Association, West Coast Section, Tumwater, Washington - September 5-6, 1980 127

COVER MICROPHOTOGRAPH: 20-day-old, late-umbo larva of Gould's shipworm /'Bankia gouldi Bartsch)
stained with oil-red O (see page 69). La/ral dimensions: length, 220 ptn; height, 240 pin. Light micrograph:
Ektachrome 200; No. 80A filter. (Micrograph by Scott Gallager, Woods Hole Oceanographic Institution,
Woods Hole, Massachusetts, 1981.)

Journal of Shellfish Research, Vol. 1, No. 1, 1-7, 1981.

GROWTH AND MORTALITY OF TWO TYPES OF SEED OYSTERS
FROM THE WANDO RIVER, SOUTH CAROLINA 1

V. G. BURRELL, JR., J. J. MANZI, AND W. Z. CARSON

South Carolina Marine Resources Research Institute,
Charleston, South Carolina 29412

ABSTRACT Two age groups of seed oysters, one less than a year old, and the other several years old, were transplanted
from the Wando River, South Carolina, to four sites in coastal South Carolina. Transplanting took place in March and in
July 1974. Growth and mortality were determined every 2 months for 1 year.

The young seed grew much faster than did the old seed, and survival was twice that of the old seed. Initial mortalities
were greater in seed transplanted in July than in March. Initial stunting of old seed from the Wando was not reflected in
subsequent growth. Factors influencing growth and survival in the Wando River are discussed.

INTRODUCTION

Historically, the South Carolina oyster industry has been
based on intertidal oysters. In recent years, however, interest
has developed in the culturing of subtidal oysters as an
alternative to lower-value intertidal oysters. A basic require-
ment for a subtidal oyster fishery is a source of high-quality
seed. Naturally occurring, well-shaped, small single oysters
grow in dense subtidal beds in the Wando River, South
Carolina, a moderately polluted estuary closed to direct
commercial shellfish harvesting. These oysters seldom grow
to more than 6.25 cm (2.5 in.) in total length and, therefore,
offer the greatest potential as seed for transplanting to
commercial or recreational growing areas.

The South Carolina Marine Resources Research Institute
has investigated growth and mortality of Wando seed oysters
transplanted to several subtidal areas in the state. This
paper compares growth and survival characteristics between
the two types of transplanted Wando seed: naturally
occurring stunted seed of unknown age, and young seed
caught on planted cultch.

MATERIALS AND METHODS

Two types of seed oysters were dredged from the Wando
River in March and in July 1974; naturally occurring
old seed attached to bits of phosphate rock, and new seed
from a bed which was established in July 1973 by planting
oyster shell. The age of naturally occurring seed was not
known. Age, however, was estimated to be at least several
years since the seed was heavily shelled and relatively unif-
orm in size. There was no indication of mortalities among
larger oysters in the river which would be evidence of
die-off upon reaching a certain age. New seed oysters caught
on planted cultch were approximately 8 and 1 1 months old
when transplanted. Seed oysters of each type (old and new)
were placed in 1-cm 2 mesh hardware cloth trays measuring
1.2 x 0.61 x 0.14 m. These trays were reinforced with

South Carolina Marine Resources Center Contribution No. 131.

1.25 cm (dia.) iron rods, and were supported on legs that
raised the trays approximately 20 cm above the bottom.
Old seed oysters were considerably larger than young seed
and were stocked at 100 per tray (160/m 2 ).New seed oysters
were stocked at 200 per tray or 320/m 2 .

Two trays containing old seed and two trays containing
new seed were placed in subtidal locations at Cape Romain
and at Dale, South Carolina. One tray of each (old and new
seed) was placed at Murrell's Inlet and in the Wando River,
South Carolina (Table 1 , Figure 1 ). All trays were positioned
in March 1974; however, those in the Wando River and at
Murrell's Inlet had to be replaced in July due to vandalism.
Cape Romain and Murrell's Inlet are important commercial
oyster growing aeas. Oysters at Dale were placed in a coastal
impoundment, and those in the Wando were planted in close
proximity to where the old seed had been obtained initially.

All oysters in each tray were examined every 2 months
to determine survival. A subsample of 50 (all, when less
than 50 remained alive) oysters from ea? h tray was measured
using Vernier calipers every 2 months during 1974, and in
January and March of 1975. Measurements to the nearest
millimeter were recorded from the umbo across the shell
over the posterior adductor muscle to the distal edge of the
shell. The experiment at Dale was terminated in September
1974, when the impoundment was drained. Water samples
for salinity and temperature determinations were taken one-
half meter above the bottom with a Kemmerer Bottle at
each sampling date. Determinations were made by refrac-
tometer and by stem thermometer, respectively.

A sample of 25 oysters growing in natural beds adjacent
to the trays in the Wando River and At Cape Romain was
examined each month (except June through September at
Cape Romain) for Perkinsus marinus (Dermo). The incidence
of infection was determined using the method of Ray
(1952) as modified by Quick (1972). Degree of infection
was estimated using criteria established by Quick and Mackin
(1971) with the exception that their very light and light
categories were combined into a single class, designated as
light; their light medium and medium into medium; and
their medium heavy and heavy into heavy.

BURRELL ET AL.

TABLE 1.

Growth and mortality study sites of seed oysters from
Wando River, South Carolina.

Location

Area Description

Murrell's Inlet A coastal estuary in northern South Carolina with
little freshwater input. Trays were placed in one of
many tidal creeks which drain extensive salt
marshes. Tray depth at low tide, 1 meter.

Cape Romain A large high-salinity estuary in Charleston County,
South Carolina, protected on the seaward side by
barrier islands and circumscribed by vast salt
marshes. Depth at study site, 1 meter at low tide.

Dale Pond A 18. 2-hectare pond on Chisolm Island in southern

South Carolina fed by South Wimbee Creek. Water
exchange is restricted and occurs only during the
last half of flood tide and first half of ebb. It is
surrounded by maritime forest and salt marsh.
Tray depth at low tide, 1 meter.

Wando River An estuary of Charleston (South Carolina) Harbor
draining approximately 134 km . It is bound on
either side by extensive salt marshes. Water depth
at the tray site was 1.5 meters at low tide.

RESULTS AND DISCUSSION

Old seed grew most rapidly at Dale Pond and at Murrell's
Inlet during the first sampling period (Figures 2 through 5).
Growth continued throughout the warm season at all
stations except at Dale Pond where growth ceased after
May. In spite of this, total length of oysters at the Dale
Pond location equaled that of other locations for the entire
warm season. The slow summer growth rate of old seed at
the Dale location may have resulted from inadequate food,
high temperature, or other factors associated with poor
water circulation in the impoundment. With the onset of
winter, growth rates decreased at Cape Romain and at
Murrell's Inlet, and continued at a reduced rate until spring.

New seed grew at a rate twice that of old seed at all loca-
tions. At the Dale location the growth rate of new seed did
not cease after May as it had in old seed, but continued until
the final observation in September. New-seed controls at
the Wando River location grew at a slow, but continuous
rate throughout the warm season and stopped during winter.
This was the same pattern observed by McGraw (1979) in
Mississippi. In a subsequent study (Manzi et al. 1977), new
seed from the same source were transplanted at age two in
October 1975 into other trays in the Wando River. The
seed averaged 45 mm at transplanting, and grew just 5 mm
in 6 months in trays (October to April). These observations
support the postulation that the majority of naturally
occurring Wando River oysters (old seed) were several years
of age, and that growth ceased at some period before the
oysters reached market size (> 75 mm). Cole and Waugli
(1959) found that early stunting in Ostrea edulis in many
instances adversely affected growth when the oysters were

MURRELLS INLET

Winyah Bay

SCALE
10 20

In ii In ill |

NAUTICAL MILES

Figure 1. Locations of oyster trays.

Seed Oysters from South Carolina

90
80
70
60

I 5°
E

E 40

Z

" 30
20

__ -

^^^^ „., '—

•-*

OLD

NEW

Figure 2. Growth of old and new seed oysters transplanted to Cape
Romain, South Carolina.

90-i
80-
70

E 60

e

S 50

E 40

_l

30
20
10

OLO
NEW

JUL

SEP

NOV

JAN

MAR

Figure 3. Growth of old and new seed oysters transplanted to
MurrelTs Inlet, South Carolina.

transplanted to suitable growing grounds. This does not
appear to be the case in transplanted Wando oysters. Young
seed did grow faster than old, but the old seed when moved
from the Wando grew at a rate expected of oysters above 3
or 4 years old. Size frequency distributions were determined
for seed derived from the Wando bed. These approximated
a normal distribution both at the beginning and at the
termination of the experiment. This, if oysters were of one
stock, would indicate that greater mortalities were not
occurring in any particular size group. Growth rates appeared
similar in all areas except for controls replanted in trays in
the Wando River location (Figure 6).

Growth data were tested for normality with a chi-square
goodness of fit test. Data were normalized with a log
[log (x + 1)] transformation and tested for homoscedasticity
with an F-max test. A two-way analysis of variance indicated
significant differences between old and new seed, and
between growth rates at the four locations. Inspection of
the growth data indicated that only the Wando River con-
trols (both old and new seed) did not conform to the rela-
tively uniform growth rates expressed at the other locations
(Figures 2 through 6).

It was not an objective of this study to determine why
growth was poor in the Wando River location, other than to

90
80
70

60 H

^ 50H

5j 40-1

30-
20
I0H

/

/

/

/

/

y

OLD

NEW

MAR MAY JUL SEP

Figure 4. Growth of old and new seed oysters transplanted to an
impoundment at Dale, South Carolina.

90-

80-

70-

60

50

40

30-1

20

io H

OLD

NEW

JUL

SEP

NOV

JAN MAR

Figure 5. Growth of old and new seed oysters transplanted to trays
in the Wando River, South Carolina.

determine if genetic influence might be a possible cause.
Several factors may enter into this phenomenon: water
circulation, food availability, temperature, salinity, turbidity,
disease, pollution, and shell pests. Salinity and temperature
may be discounted because neither approached established
extremes of oyster tolerance (Figures 7 and 8) (Galtsoff
1964); temperature never fell below that at which the
oyster ceased to pump. Shell pests such as Polydora or
Cliona were not present on Wando beds to the extent
that they persisted at the other tray sites. Food supply
may have been a factor, while density on the Wando beds
was much less than Haven et al. (1978) reported on leased
grounds in Virginia, the amount of food available in the
Wando may have been more limited. Circulation in regard
to current flow was adequate as evidenced by a 2-m semi-
diurnal tide. Silt load carried by the tidal current may be

BURRELL ET AL.

OLD SEED

1974

1975

NEW SEED

1974

1975

MURRELLS
INLET

CAPE

ROMAIN

DALE

30-
25-
20-
15-
10-
5-
0-

40-

35-

30-

£25-

jS 20-

£ 15-

° 10-

5-

0-

fc 40-

35-

30-

25-

k 20-

H 15-

1 10-

z 5-

0-

50 I 70 50 I 70 I 90

60

WANDO
RIVER

25-

20-

15-

10-

5-

0-

40 I 60 I 80
50 70 90

60 80

60 I 80 I 100 70 I 90 I

i | i I i

50 I 70 I 90 60 I 80

60 80

20 I 40
30 50

40 I 60 I 80 I 50 I 70 I 20 I 40 I

60 80 30 50

LENGTH IN MM

50 I 70 I 90
60 80

50 I 70 I 90
60 80 100

4t4

60 I 80 I 20 I 40 I 40 I 60 I 80
70 90 30 50 50 70

30 I 50 I
40 60

Figure 6. Growth in mm of transplanted seed oysters.

Seed Oysters erom South Carolina

40-

50-

a

a

>

i-

Z20-

^**"\

_l

,-"

■

*•* V

. .«•* \

10-

\

\

\

MURRELLS
"INLET

- CAPE ROMAN
-DALE

- WANDO RIVER

MAR MAY JUL SEP NOV JAN MAR

Figure 7. Salinity at tray locations during study period.

implicated if it was such that it reduced feeding time and
shell-generating activities of the mantle (Cole and Waugh
1959). There was also a possibility that factors such as
heavy metals may play some role in reducing growth.
In a study of several metals, only copper concentrations in
Wando oysters were unusually high when compared with
concentrations in other growing areas. The Wando River
copper concentration had an average of 108 jug/g as com-
pared to an average of 19 /ug/g at ten other South Carolina
locations (Mathews and Boyne 1979). Shuster and Pringle
(1969), however, found that copper apparently enhanced
growth in oysters, so a direct affect here did not appear
likely.

Survival data were normalized with an arcsine trans-
formation and tested for homogeneity of variance with an
F-max test. A two-way analysis of variance indicated a
significant difference in survival between old and new seed,
but no difference in survival rates between the four locations.

Mortality exceeded 50% of old seed at all locations
except for the Wando River controls. Highest mortalities
were recorded in the July transplant at the Wando River
and Murrell's Inlet sites (Table 2). This could be a result of
high air temperatures and concomitant dessication during
transplanting. Highest mortalities were recorded in summer
and fall, characteristics of those associated with Perkinsus
marinus (Andrews and Hewatt 1957). Incidence of infection
in Wando River and Cape Romain oysters was similar to
that reported by Quick and Mackin (1971) in Sarasota Bay,
showing a spring minimum and fall-winter maximum. After
initial mortality, possibly associated with replanting, few
additional old oysters died in the Wando River controls.
Salinity may have been low enough for a sufficient time to
control Perkinsus marinus in the Wando River controls as
postulated by Quick and Mackin (1971); however, a similar
decrease in infection was observed at Cape Romain where
salinity remained high (Figures 9 and 10). Incidence and
intensity of infection were remarkably similar at the two
locations, making it difficult to attribute high mortalities
in Cape Romain to Perkinsus marinus when they were not
observed in the Wando River controls. As expected,

D
< 20

CAPE ROMAIN
DALE
WANDO RIVER

MAR MAY JUL SEP NOV JAN MAR
Figure 8. Temperature at tray locations during study period.

mortality was low in winter at Cape Romain (Tray 1) and
at the Wando River sites; however, at Cape Romain (Tray 3)
and at MurreLTs Inlet, high mortality was recorded on two
cold weather sampling dates. These deaths could not be
explained.

TABLE 2.

Percent mortality of new and old seed oysters during study period.

Cumulative mortality is shown in first column, and

relative mortality in parenthesis.

Tray 1

Tray 2

Tray 3

Tray 4

Old

New

Old

New

Cape Romain

March 1974

—

—

—

—

May

2 (2)

1

(2)

1 (1)

8 (8)

July

12 (10)

3

(2)

6 (5)

11 (3)

September

36 (27)

6

(3)

27 (22)

14 (3)

November

52 (25)

12

(6)

34(10)

19 (5)

January 1975

54 <<1)

14

(2)

52(27)

19 (0)

March

56 (<1)

21

(8)

55 (6)

20 (2)

Dale Pond

March 1974

—

—

—

—

May

16 (16)

9

(9)

4 (4)

3 (3)

July

37 (25)

11

(3)

26 (23)

3 (6)

September

58 (33)

23

(13)

47 (28)

22 (10)

Murrell's Inlet

July 1974

—

—

September

53 (53)

16

(16)

November

58 (11)

21

(7)

January 1975

58 (0)

22

«D

March

73 (36)

22

«D

Wando River

July 1974

—

—

September

21 (21)

9

(9)

November

24 (4)

13

(4)

January 1975

25 (1)

16

(3)

March

27 (3)

20

(5)

BURRELL ET AL.

□ light

MEDIUM
■ HEAVY

n^ MAR
Q FEB

MAY

APR

MAR

FEB

JAN 1974

No Infection

□ LIGHT
£3 MEDIUM
■ HEAVY

L.

MAR
FEB
□ JAN 1975
DEC

gS N0V

^ OCT

No Sample
No Sample
No Sample
No Sample

T

Lx

SEP
AUG
JUL
JUN
MAY
APR
^ MAR
FEB
JAN 1974

1 1 1 1 1

o o o o o

PERCENT INFECTION

Figure 9. Percent and intensity of Perkinsus marinus infection in Figure 10. Percent and intensity of Perkinsus marinus infection in
oysters from Wando River, South Carolina, January 1975 - oysters from Cape Romain, South Carolina, January 1974 -
March 1975. March 1975.

O O O O O

to <j- ro CJ —

PERCENT INFECTION

Total mortality in young seed ranged from 20 to 22%, or
less than half that for older seed. This again followed the
Perkinsus marinus pattern described by Andrews and
Hewatt (1957) which showed young oysters to be less
susceptible to infection by this pathogen than older oysters.
Mortality of oysters following transplanting was greater in
July than in March, and was more pronounced among old
than new seed.

CONCLUSIONS

Young seed oysters grew faster than older seed oysters
when transplanted from the Wando River to other South
Carolina growing areas. Early stunting in the older seed
oysters did not appear to be reflected in subsequent growth
rates. Mortalities, however, were much higher in older seed
than in younger seed, and were greater when transplanting
was carried out in summer than in winter.

Seed Oysters erom South Carolina

Causes of mortality need to be investigated, and the
impact of Perkinsus marinus in South Carolina waters
needs clarification. Further studies are needed to assess
growing potential of young seed on various oyster
grounds. In addition, planting on natural bottoms in large
enough quantities to project economic feasibility is
necessary.

ACKNOWLEDGMENTS

The authors thank Drs. Paul Sandifer and Ted Smith,
and Mr. Bill Anderson for their suggestions and editorial
comments; Ms. Karen Swanson for drafting illustrations,
and Mrs. Debra Farr for typing the manuscript. This work
was funded in part through the National Sea Grant Program
under Grant Nos. 04-5-158-5 and 04-6- 158-44009.

references cited

Andrews. J. D. & W. G. Hewatt. 1957. Oyster mortality studies in

Virginia. II. The fungus disease caused by Dermocystidiwn

marinus in oysters of Chesapeake Bay. Ecol. Monogr. 27:1—25.
Cole, H. A. & G. D. Waugh. 1959. The problem of stunted growth in

oysters./ Cons. Cons. Int. Explor. Mer. 24:355-365.
Galtsoff, P. S. 1964. The American oyster, Crassostrea virginica

Gmelin. U.S. Fish Wild!. Serv. Fish. Bull. 64. 480 pp.
Haven, D. S., W. J. Hargis, Jr. & P. C. Kendall. 1978. The oyster

industry of Virginia: Its status, problems, and promise. Va.

Inst. Mar. Sci. Spec. Pap. Mar. Sci. No. 4. 1024 pp.
Manzi, J. J., V. G. Burrrell & W. Z. Carson. 1977. A comparison of

growth and survival of subtidal Crassostrea virginica (Gmelin)

in South Carolina salt marsh impoundments. Aquaculture

12:293-310.
Mathews, T. D.& J. V. Boyne. 1979. The distribution of copper and iion

in South Carolina oysters. J. Environ. Sci. Health 14(8):683-694.

McGraw, K.. A. 1979. Growth and survival of hatchery-reared and

wild oyster spat in Mississippi Sound and adjacent waters. Proc.

Nat. Shellfish. Assoc. 69:198 (Abstract).
Quick, J. A. 1972. Fluid thioglycoUate medium assay of Labyrin-

thomyxa parasites in oysters. Fla. Dep. Nat. Resour. Mar. Res.

Lab. Leaf. Ser. Vol. 6. Chemistry. 12 pp.
& J. G. Mackin. 1971. Oyster parasitism by Labyrinthomyxa

marina in Florida. Fla. Dep. Nat. Resour. Mar. Res. Lab. Prof.

Pap. Ser. 13.55 pp.
Ray, S. M. 1952. A culture technique for the diagnosis of infection

with Dermocystidium rnarinum in oysters. Nat. Shellfish. Assoc.

Convention Address No. 9-13. [Also: same title in Science

116:360-361. 1952.)
Shuster, C. N., Jr. & B. H. Pringle. 1969. Trace metal accumulation

in the American eastern oyster, Crassostrea virginica. Proc. Nat.

Shellfish. Assoc. 59:91-103.

The NATIONAL SHELLFISHERIES ASSOCIATION gratefully
acknowledges the monetary gift from MR. WALLACE GROVES and
the WALLACE GROVES AQUACULTURE FOUNDATION of
Freeport, Bahama, for the support of this volume of the JOURNAL
OF SHELLFISH RESEARCH. Only through the support of indi-
viduals and organizations whose interests are served by shellfish
research is publication of this journal possible. The Association seeks
public and private, tax-deductible contributions for the support of its
activities including this publication.

Journal of Shellfish Research, Vol. 1. No. 1, 9-16, 1981.

SOME RELATIONSHIPS BETWEEN GAMETOGENIC CYCLE AND SUMMER MORTALITY

PHENOMENON IN THE PACIFIC OYSTER (CRASSOSTREA GIG AS)

IN WASHINGTON STATE 1 ' 2

JAMES A. PERDUE, JOHN H. BEATTIE AND KENNETH K. CHEW

College of Fisheries, University of Washington,
Seattle, Washington 98195

ABSTRACT During the summer of 1979, both commercial and experimental (F 2 ) oysters experienced summer mortal-
ities in three commercial production areas. Mortalities among the experimental families were variable, ranging from 11% to
94.6%. Carbohydrate content and gonadal development were compared between those families that exhibited low and high
mortalities. In all groups, carbohydrate levels dropped sharply from 25 to 30% in May to values as low as 3% in some
families by late summer. The decline in carbohydrate content was negatively correlated with increased gonadal development.
Absolute levels of carbohydrate could not be directly correlated to either high or low mortality; however, timing of mortality
consistently occurred during the storage phase of the carbohydrate cycle, just following spawning and/or reabsorption.
There was evidence that mortality was selective for females.

INTRODUCTION

Significant summer mortalities of Pacific oysters, Crassos-
trea gigas, have occurred in commercial growing areas of
Washington State since the 1960's. The pattern of mortality
was similar to that observed among Pacific oysters in Japan.
In both Japan and the United States, growers had to resort
to such methods as overplanting, transplanting, and early
harvesting to "farm around" this summer mortality
(Ogasawara et al. 1962, Scholz 1975). During the early to
mid-1 970's, the incidence of summer mortality was almost
completely absent in Washington State, but beginning in
1976, increasing numbers of oyster-growing areas in southern
Puget Sound experienced significant mortalities. In 1979, at
least five bays in southern Puget Sound suffered significant
mortalities among commercially harvestable oysters, with
one growing area experiencing a 60% mortality of marketable
oysters.

Research efforts in both the United States and Japan
during the 1 960's established the now , well-known character-
istics of summer mortality (Glude 1975, Koganezawa 1975).

In both Japan and the United States, mortalities invariably
occurred: (1) among two-year-old or older stocks, (2) in
areas of high nutrient levels and high productivity, (3)
during the late summer months when water temperatures
approached 20°C and above, and (4) among oysters with
relatively high condition indices.

Although the characteristics of summer mortality are
well known, no direct cause has been clearly established.
Japanese research indicated that summer mortalities were
associated with abnormal gonadal maturation of oysters
cultured in eutrophic bays, which resulted in physiological
stress (Mori 1979). Lipovsky and Chew (1972) showed that
mortalities of C. gigas could be induced in the laboratory

Supported by the Washington Sea Grant Program under the National

Oceanic and Atmospheric Administration, U.S. Department of

Commerce.

Contribution No. 56 2, College of Fisheries, University of Washington.

under conditions of elevated water temperatures (greater
than 18°C) and high nutrients. Large numbers of bacteria
(Vibrio spp.) were found in moribund oysters; it was believed
they played a significant role in the laboratory mortality.
However, recent histological studies of moribund oysters
from field mortalities have shown no evidence of bacterial
infection (Dr. Marsha Landolt, personal communication).

In an effort to control summer mortality, the University
of Washington established a selective breeding program to
develop strains of Pacific oyster resistant to summer mor-
tality (Beattie et al. 1978), Initially, survivors from thermal
challenges in the laboratory were utilized, but with the
reoccurrence of mortality, survivors of field challenges now
are being used as broodstock for subsequent generations.
Results of field studies in 1978 and 1979 appear promising,
because a majority of experimental families have exhibited
better survival than unselected control stocks (Beattie et al.
1978).

In addition to the selective breeding work, research at
the University of Washington has been focused on the
etiology of summer mortality; the reproductive cycles of
experimental families exhibiting both high and low mor-
talities during field challenges have been compared. A
baseline study was conducted during the summer of 1979
that compared the reproductive cycles of experimental
groups of oysters during the observed mortality.

MATERIALS AND METHODS

Sampling Program

Oysters from 23 experimental families (F 2 ) selectively
bred for survival, and control oysters were monitored for
mortality in three bays in southern Puget Sound, that
previously had exhibited high mortalities: Rocky Bay,
Oakland Bay, and Mud Bay (Figure 1). Samples of all
tamilies were planted initially in all three bays. However,
early spat mortality (due to siltation and predation)

10

Perdue and Chew

Figure 1. Locations of the three sampling areas in southern Puget
Sound.

completely eliminated some families and diminished the
numbers in other families below a level adequate for a com-
plete sampling regime. Only families with adequate numbers
of individuals were selected for analysis of gametogenesis
and carbohydrate content (Table 1). A group of unselected,
commercially caught seed from Dabob Bay, Washington
(hereafter termed "Dabob control"), also was monitored in
each bay. This group served as the control in evaluating the
survival performance of the selected experimental families.
Fifteen oysters from the preselected experimental families
were sampled bimonthly from May through August, and
monthly from September through December. Ten oysters
from each sample were fixed in 1 0% formalin and sectioned
for determination of gonadal development. The remaining
five animals were used for determination of carbohydrate
content.

Histology

Cross sections from oysters were cut through the mid-
visceral mass behind the labial palps. Following imbedding
in paraffin, 6 Attn sections were stained in Myers hematoxylin
and counterstained in picroeosin. Sections were then
enlarged 13 times and gonadal development assessed using
the quantitative morphological analysis of Chalkley ( 1943)
as modified for oysters by Mori (1979). Percent develop-
ment was determined by comparing the gonadal area with
the total morphologic area in the cross section. Area was
determined using either a point-counting system or a polar
planimeter. In addition to gonad, digestive tubule areas also
were determined in each animal.

Carbohydrate

Carbohydrate was determined on freeze-dried homo-
genized tissue from the five pooled animals of each group.
Determinations were made by extracting 5 to 15 mg of
freeze-dried tissue in trichloroacetic acid as described by
Mann (1978). Carbohydrate was assayed using the methods
of Strickland and Parsons (1972). Calibration was against
oyster glycogen (Sigma Chemical Co., Type II).

RESULTS

Significant mortalities occurred among the experimental
families and the control group in all three bays, with
individual families exhibiting a wide range of cumulative
mortalities (Table 1). Experimental families preselected for
analysis of reproductive parameters represented both high
and low mortaility groups in Mud and Oakland bays. In
Rocky Bay, however, the preselected groups exhibited
similar cumulative mortalities. Timing of the mortality
differed between bays (Figure 2). Mortalities among experi-
mental animals in Mud, Oakland, and Rocky bays peaked in
early August, early September, and early October,
respectively.

Figure 2. Percent mortality of all experimental oysters in Rocky,
Oakland, and Mud bays in 1979.

Carbohydrate levels among oysters in the selected experi-
mental families and in the Dabob control in all three bays
exhibited a distinct sequence of change, with three discern-
ible phases (Figures 3 through 5) during the sampling
period May through December 1979. The first phase
occurred from May through July, and was marked by an
abrupt decline in percent carbohydrate from levels of 20 to
30% in late May to levels as low as 3 to 5% in July. During
the second phase, percent carbohydrate remained at rela-
tively low levels with few families exhibiting large fluctua-
tions. The third phase was marked by a transition to
increased carbohydrate levels again, which, by December,
reached 70 to 80% of the May levels. Both timing and
degree of change of this third phase varied between bays. In
all three bays, however, the timing of the transition to

Gametogenic Cycle and Mortality in Pacific Oysters

11

TABLE 1.

Cumulative mortalities (%) of experimental families and the control (Dabob) in each
of the three study areas as of December 1979.

Mud Bay

Oakland Bay

Rocky Bay

Cumulative

Cumulative

Cumulative

Family

Number

Mortality (%)

Family

Number

Mortality (%)

Family

Number

Mortality (%)

6-28AX

102

23.6

*1-16AX

520

11.3

6- 3AX

157

21.0

6- 3AY

69

26.1

7-29BX

170

15.3

8-15AX

120

23.4

*8- 5BY

366

31.0

8-23BX

120

17.5

7- 1AY

148

23.7

6-27AZ

99

34.3

8- 2BX

260

20.0

*-15BY

96

25.0

7-20BX

264

34.9

6-27BX

70

22.9

*6-28BX

190

30.0

6-27AY

77

36.4

7- 1AY

189

23.3

8- 2BX

118

33.0

*8-23AX

354

37.4

5- 3BY

276

26.1

*Dabob

264

35.2

7- 1AY

141

44.7

6-28BX

81

26.8

8-23BX

154

38.4

8- 2BX

190

45.3

*6-27AY

516

27.4

*6-27AY

446

38.9

8- 5AY

28

46.5

8- 3AY

358

32.8

8- 5AY

94

46.8

5- 3BY

137

48.2

*1-16BX

243

33.6

6- 3BY

71

49.3

6- 3BY

31

51.6

7-25AX

77

33.8

8-23AX

229

54.1

8-23BY

187

56.1

6- 3AX

219

35.1

7-25AY

114

54.4

* Dabob

249

56.1

8- 5AX

46

39.2

7-25 AX

113

54.9

*8- 3AY

501

64.2

8-15BY

95

40.0

8- 5BY

170

57.0

7-25AX

68

66.2

6-22AY

50

42.0

8-15H

94

59.6

7-25AY

89

85.4

8- 5BY

167

43.2

8- 3AY

126

60.3

7-25AY

42

47.7

7-20BX

197

84.2

6-27AZ

83

50.6

6-27AZ

85

84.8

7-25BY

11

54.6

*Dabob

549

56.6

8- 5AY

19

57.9

8-23AX

21

76.2

7-20BX

333

90.4

8-15H

55

94.6

* Analyzed for physiological parameters.

NOTE: Family codes refer to date of spawning, and female and male used. For example, 6-28AX refers to a family resulting from a

spawning of female "A" and male "X" on June 28. All spawnings occurred in 1977, and in January 1978. Family 8- 15H

was a functional hermaphrodite.

tjt — i — i — rp — pn — rp — r^

- 1 — rr -1 — r~

r-r-i — r— i r-p-

35-

\

■ -

\

2b-

■ \

.

■ -

''H

y/s'

is-

jy .--■*''

:''-'- '

le-
s'

\'

x^.

~

-= 1-16 AX
. BIB*

'1 ■ \J ■ 1 1

JUL*

i ' '.„»' ■ i ■

SEP

1 ■ -oc." '

1 NOV '

Figure 3. Percent (dry weight) carbohydrate of two experimental Figure 4. Percent (dry weight) carbohydrate of two experimental
families and the control in Rocky Bay, Washington. Arrows indicate families and the control in Oakland Bay, Washington. Arrows
period of peak mortality. indicate period of peak mortality.

12

PERDUE AND CHEW

increase carbohydrate levels (third phase) was associated
with the timing of peak mortality (Figures 3 through 5).

-r-T 1 1 rj-\ 1 1 1 — | — I 1 —

| ' ' or / — i-p — r^T — r-p-

Figure 5. Percent (dry weight) carbohydrate of three experimental
families and the control in Mud Bay, Washington. Arrows indicate
period of peak mortality.

In both Rocky and Oakland bays, carbohydrate levels
were similar among the experimental families sampled
(Figures 3 and 4). In contrast, experimental families in
Mud Bay exhibited variability in both carbohydrate levels
and the timing of the late summer increase in percent carbo-
hydrate (Figure 5). Experimental family 8— 5 BY exhibited
carbohydrate values at least 50% greater than any other
group sampled in Mud Bay from June through mid-August.
In fact, percent carbohydrate in this family never went
below 17.0% during the sampling period, which was higher
than any group monitored from any bay. Experimental
family 8— 3AY and the Dabob control group in this bay
exhibited abrupt increases in percent carbohydrate character-
istic of the third phase described earlier. Both of these
groups exhibited high cumulative mortalities (Table 1).
Experimental family 8— 23AX in Mud Bay exhibited pro-
longed low levels of percent carbohydrate, taking 3 months
to attain levels of 15% or greater (Figure 5).

A comparison of a high mortality group (Dabob) and a
low mortality group (1 — 1 6 AX) in Oakland Bay revealed a
similar relationship (Figure 4). During the mortality period
in this bay, an abrupt increase in percent carbohydrate was
noted in the high mortality group (Dabob), although the
increase was not as dramatic as was observed in the high-
mortality group in Mud Bay. Experimental family 1 — 16AX,
on the other hand, exhibited a more gradual increase in
carbohydrate levels during the mortality period.

Results of gonadal development of sampled experimental
families are presented in Figures 6 through 8 for Rocky,
Oakland, and Mud bays, respectively. Only groups that
exhibited either high or low mortality are presented for
comparison. Generally, gonadal size increased quickly
during June and early July in all bays. Gonadal development

peaked from late July to early August with gonadal tissue
occupying 65 to 75% of the total cross-sectional area.
Gonadal development then declined to lower levels. In
some groups, the decline in late summer was dramatic.

-• 6 27AV
-o 6-28BX

' I i — ' — i — •—r

Figure 6. Gonadal development based on cross section percentage
of two experimental families in Rocky Bay, Washington, in 1979.
Standard error represented by brackets. Arrows indicate period of
peak mortality.

Ir

Figure 7. Gonadal development based on cross section percentage of
two experimental families in Oakland Bay, Washington, in 1979.
Standard error represented by brackets. Arrows indicate period of
peak mortality.

Gametogenic Cycle and Mortality in Pacific Oysters

13

J UN ' JUL I Aug I SEP I

Figure 8. Gonadal development based on cross section percentage of
two experimental families in Mud Bay, Washington, in 1979.
Standard error represented by brackets. Arrows indicate period of
peak mortality.

going from levels greater than 60% to levels approaching
30% in less than one month. Examination of these sections
indicated evidence of spawning. Experimental families that
exhibited a more gradual decline in gonad size showed
extensive infiltration by leucocytes with little or no
spawning occurring. In all three bays, the timing of mortality
coincided with the decrease in gonad size. All groups
examined showed an inverse relationship between gonadal
development and carbohydrate content.

In addition to the gonad, digestive tubule area fluctuated
during the summer in all groups observed. Examples are
presented in Figures 9 and 10 for two families in Mud Bay.
As the gonad developed in each family, less area was
occupied by the digestive tubules. By midsummer when
gonadal development had peaked, digestive tubules occupied
approximately one half the area they did in May. As
spawning and/or reabsorption progressed and gonad size
declined, digestive tubule area increased. Gonadal area and
digestive tubule area were negatively correlated. For example ,
the correlation between gonad and digestive tubule areas
for the two families in Figures 9 and 10 was r = -0.9904 for
family 8-5BY, and r = -0.9165 for family 8-3 AY. Simi-
larly, high negative correlations were noted for the other
experimental families and controls observed.

Sex ratio of each experimental group was compared
between the period prior to peak mortality and the period
after peak mortality. Experimental groups that exhibited
either high or low mortality in Mud Bay and in Oakland
Bay are compared in Figures 1 1 and 1 2 (Mud Bay), and in
Figures 13 and 14 (Oakland Bay). In both cases, the

percentage of females declined significantly in experimental
groups exhibiting high mortality, while the percentage
of females remained the same in experimental groups
exhibiting low mortality, indicating that mortality was
selective for females.

,/1

i/N

----. DIGESTIVE TUBULES

•— • GONAD

III 1 1 III 1

1 J UN 1 J

JL 1 au(

i r t-i 1 1-7-1 1

1 SEP 1

Figure 9. Changes in gonad and digestive tubule areas based on
cross section percentage in experimental family 8-5BY in Mud Bay,
Washington. Standard error represented by brackets.

Figure 10. Changes in gonad and digestive tubule areas based on
cross section percentage in experimental family 8 3AY in Mud Bay
Washington. Standard error represented by brackets.

14

Perdue and Chew

Figure 1 1 . Percentage comparison of females in experimental family
8-5BY in Mud Bay, Washington, before occurrence of mortality
(samples prior to July 24; N = 44), and after occurrence of mortality
(samples after July 24, inclusive; N = 49).

Figure 12. Percentage comparison of females in experimental family
8-3AY in Mud Bay, Washington, before occurrence of mortality
(samples prior to July 24; N = 41), and after occurrence of mortality
(samples after July 24, inclusive; N = 5 1).

T

I

t ryn I r-|— i I I r-i i
; I SEP I oci l

Figure 13. Percentage comparison of females in experimental family
1-16AX in Oakland Bay, Washington, before occurrence of
mortality (samples prior to August 21 ; N = 59), and after occurrence
of mortality (samples after August 2 1 , inclusive; N = 40).

Figure 14. Percentage comparison of females in control (Dabob)
group in Oakland Bay, Washington, before occurrence of mortality
(samples prior to August 21; N = 58), and after occurrence of
mortality (samples after August 2 1 , inclusive; N = 36).

DISCUSSION

The wide range of cumulative mortalities observed among
experimental families in each bay during this study is similar
to results obtained during the field mortality observed
among experimental groups in 1978, when mortalities
ranged from 5 to 86% among 13 families (Beattie et al.
1980). The occurrence of experimental families exhibiting
both high and low mortalities provides not only a valuable
source of broodstock for selective breeding, but also an
opportunity to better understand the etiology of summer
mortality.

Results from this baseline study confirm the close rela-
tionship observed between summer mortality and the
gametogenic cycle of C. gigas, first noted by Japanese
researchers in the 1960's. They pointed out that oysters
in areas of low mortality exhibited relatively high levels of
glycogen and less extensive gonadal development, while
oysters from high mortality areas exhibited extremely low
glycogen levels and more extensive gonadal development
(Mori et al. 1965). Results from this study indicate that
there is no relationship between the absolute levels of carbo-
hydrate and either high or low mortality exhibited in the
experimental groups. There is evidence, however, that the
timing of mortality coincides with a change in carbohydrate
metabolism to a storage phase. It is possible that these
increased levels of carbohydrate are partially due to a post-
mortality selection of animals with higher levels of carbo-
hydrate, although familes such as 8— 23AX (Figure 5) and
1— 16BX (Figure 4) would suggest that this is not the case.

The timing of mortality also coincides with the period
when the gonad is most extensively developed and has
begun to decrease, abruptly in groups that have spawned
and more gradually in groups that have not spawned. The
relationship between spawning and observed mortalities
must be studied in more detail before any conclusions
can be made.

The decline in digestive tubule area to levels approaching
40 to 50% of the May levels indicates that changes in tissues
other than connective tissue occur during gametogenesis.
Part of this decrease is due to an increase in tubule density.
The high inverse correlation noted between digestive tubule
area and gonadal area in C. gigas suggests that the process of
gonadal maturation may occur at the expense of digestive
tubules, similar to that found in M vtilus edulis (Thompson
et al. 1974). Tamate et al. (1965) noted that digestive
tubules of Pacific oysters in high mortality areas exhibited
cellular destruction compared to those oysters in low
mortality areas. In this study, digestive tubule area declined
equally between high mortality groups and low mortality
groups, and was dependent entirely on changes associated
with the gonad. Morton (1977) indicated that the digestive
diverticula of C. gigas undergoes a synchronized pattern of
cytological changes in a sequence related to tidal as well as
seasonal cycles. In summer, he found that the digestive
tubules exhibited a short phase of absorption and a longer

Gametogenic Cycle and Mortality in Pacific Oysters

15

phase in which interior cellular components (fragmentation
spherules) broke down and were removed as fecal matter
through the gut. Whether that process resulted in stress on
the animal is unclear, but absorptive efficiency could con-
ceivably decline as a result.

Sex ratio data indicated that mortality was selective
against females, although male oysters were observed to die.
This contradicts results obtained during the 1960's in
Washington state where no difference in mortality was
noted between males and females (Glude 1975). Although
carbohydrate was not analyzed in females and males
separately, there is evidence that, in the Pacific oyster,
females deplete carbohydrate reserves faster and to a greater
extent relative to males (Matsumoto et al. 1 934, Mori et al.
1965).

Crassostrea gigas, like many other bivalves, undergoes a
marked seasonal cycle of gametogenic activity, which has
been linked with storage and utilization of reserve materials
in the body (Mori et al. 1965). Carbohydrate levels in the
Pacific oyster have been shown to vary inversely with
gonadal development (Matsumoto et al. 1934, Mann 1978).
The fate of carbohydrate reserves in bivalve molluscs during
gametogenesis is probably as a respiratory substrate and as
the precursor of lipid reserves of the developing eggs
(Gabbott 1975, Holland and Hannant 1974). Data from
this study underscore the relationship between gonadal
maturation and carbohydrate depletion.

Control of carbohydrate metabolism in bivalves has been
studied extensively (Bourcart and Lubet 1965, Gabbott
1975, Sastry and Blake 1971). Generally it is assumed that

the reproductive cycle is controlled internally by neuro-
hormones, and that external factors such as temperature
and food act as synchronizers. The variability in the carbo-
hydrate cycle and gonadal development of experimental
groups in Mud Bay indicates that the response to environ-
mental cues may have a strong genetic component. This
suggests a potential for selective breeding for there are
obvious market advantages for an oyster that maintains
relatively high levels of carbohydrate and, consequently,
delays gonadal development into the summer months as
exhibited by experimental family 8— 5 BY in Mud Bay
(Figure 5).

Results from this study confirm the relationship noted
by Japanese researchers between summer mortality and
aspects of the reproductive physiology of C. gigas. Environ-
mental characteristics, such as long periods of exposure,
warm temperatures, and dinoflagellate blooms, could con-
ceivably "trigger" the mortality among animals already in a
stressed state. Environmental studies are now underway
that will coincide with continued studies of the reproductive
physiology of experimental families (F 3 ). The combined
studies will contribute further input into the etiology of
summer mortality.

ACKNOWLEDGMENTS

The authors express their gratitude to Mr. Harold
Wiksten, Minterbrook Oyster Company, and to Mr. Justin
Taylor, Taylor United Incorporated, for use of portions of
their commercial oyster grounds.

REFERENCES CITED

Beattie, J. H., W. K. Hershberger, K. K. Chew, C. Mahnken, E. F.
Prentice & C. Jones. 1978. Breeding for resistance to summer-
time mortality in the Pacific oyster (Crassostrea gigas). Washing-
ton Sea Grant Publication WSG 78-3. 13 pp.

Beattie, J. H., K. K. Chew, & w. K. Hershberger. 1980. Differential
survival of selected strains of Pacific oysters (Crassostrea gigas)
during summer mortality. Proc. Nat. Shellfish. Assoc. 70(1):
119 (Abstract).

Bourcart, C. & P. Lubet. 1965. Cycle sexuel et evolution des reserves
chez Mytilus galloprovincialis Lmk (Mollusque bivalve). Rapp.
P.-V. Reun. Commn. Int. Explor. scient. Mer Meditter., T. 18:
155-158.

Gabbott, P. A. 1975. Storage cycles in marine bivalve molluscs:
A hypothesis concerning the relationship between glycogen
metabolism and gametogenesis. Pages 191-211 in Proc. 9th
Europ. Mar. Biol. Symp., Aberdeen, Scotland.

Glude, J. B. 1975. A summary report of Pacific Coast oyster
mortality investigations 1965-1972. Pages 1-28 in Proc. Third
U.S.-Japan Meeting on Aquaculture. Tokyo, Japan, October 15-
16, 1974.

Holland, D. L. & P. J. Hannant. 1974. Biochemical changes during
growth of the spat of the oyster, Ostrea edulis L. J. Mar. Biol.
Assoc. U.K. 54:1004-1016.

Koganezawa, A. 1975. Present status of studies on the mass mortality
of cultural oysters in Japan and its prevention. Pages 29-34 in

Proc. Tliird U.S.-Japan Meeting on Aquaculture. Tokyo, Japan,
October 15-16, 1974.

Lipovsky, V. P. & K. K. Chew. 1972. Mortality of Pacific oysters
(Crassostrea gigas): the influence of temperature and enriched
seawater on survival. Proc. Nat. Shellfish. Assoc. 62:72-82.

Mann, R. 1978. Some biochemical and physiological aspects of
growth and gametogenesis in Crassostrea gigas and Ostrea edulis
grown at sustained elevated temperatures. J. Mar. Biol. Assoc.
U.K. 58:95-110.

Matsumoto, B., M. Matsumoto & M. Hibino. 1934. Biochemical
studies of Magaki (Ostrea gigas). II. The seasonal variation in the
chemical composition of Ostrea gigas Thunbeig. J. Sci. Hiroshima
Univ. A4:47-56.

Mori, K.. 1979. Effects of artificial eutrophication on the metabo-
lism of the Japanese oyster, Crassostrea gigas. Mar. Biol. 53:
361-369.

, H. Tamate, T. Imai & O. Itikawa. 1965. Changes in the

metabolism of lipids and glycogen of the oyster during the
stages of sexual maturation and spawning. Bull. Tohoku Reg.
Fish. Res. Lab. 25:65-88.

Morton, B. S. 1977. The tidal rhythm of feeding and digestion in
the Pacific oyster, Crassostrea gigas (Thunberg). J. Exp. Mar.
Biol.Ecol. 26:135-151.

Ogasawara, Y., U. Kobayashi, R. Okamoto, A. Furukawa, M. Hisaoka
& K. Nogami. 1962. The use of hardened seed oyster in the

16

PERDUE AND CHEW

culture of the food oyster, C. gigas (Thunberg) and its signifi-
cance to the oyster culture industry. Fish. Res. Inst., Naikaiku
Fish. Agency No. 103. 5 pp.

Sastiy, A. N. & N. J. Blake. 1971. Regulation of gonad development
in the bay scallop, Aequipecten irradians Lamarck. Biol. Bull.
(Woods Hole) 140:274-283.

Scholz, A. J. 1975. Pacific oyster mass mortality studies; seasonal
summary report No. 5. Washington Dept. Fish., May 1975.
Report to National Marine Fisheries Service. 20 pp.

Strickland, J. D. H. & T. R. Parsons. 1972. A practical handbook of

seawater analysis. Bull. Fish. Res. Board Can. No. 167.

310 pp.
Tamate, H., K. Numachi, K. Mori, O. Itikawa & T. Imai. 1965.

Studies on the mass mortality of the oyster in Matsushima Bay:

Pathological studies. Bull. Tohoku Reg. Rish. Res. Lab. 25:

89-104.
Thompson, R. I., N. A. Ratcliffe & B. L. Bayne. 1974. Effects of

starvation on structure and function in the digestive gland of

the mussel (Mytilus edulis L.). J. Mar. Biol. Assoc. U.K. 54:

699-712.

Journal of Shellfish Research, Vol. 1, No. 1, 17-21, 1981.

SPAWNING OF THE CALICO SCALLOP ARGOPECTEN GIBBUS
IN RELATION TO SEASON AND TEMPERATURE 1

GEORGE C. MILLER, DONALD M. ALLEN AND T. J. COSTELLO

Southeast Fisheries Center, National Marine Fisheries Service,
National Oceanic and A tmospheric Administration,
75 Virginia Beach Drive,
Miami, Florida 33149

ABSTRACT Analysis of previous research demonstrated that most spawning of the calico scallop Argopecten gibbus off
Cape Canaveral, Florida, occurred between November and June. In 1970 and 1971, spawning intensity was highest from
January to May when bottom water temperatures were below 22.5 C, and lowest from June to October when temper-
atures were usually above 22.5 C. Major spawning occurred when bottom water temperatures ranged from about 15.0 to
22.5 C at depths from 18 to 55 m (the zone of calico scallop concentrations).

Off Cape Canaveral, bottom water temperatures in the calico scallop zone are strongly influenced by seasonal atmos-
pheric temperatures and by intrusions onto the Florida-Hatteras Shelf of deep, cold water. Movement of cold water from
inshore or offshore into the scallop zone apparently initiates spawning.

Calico scallops are most abundant near Cape Canaveral and Cape San Bias, Florida, and Cape Lookout, North Carolina.
Cold water intrusions near these capes produce environmental conditions that may be favorable or unfavorable to scallop
abundance.

INTRODUCTION

The calico scallop Argopecten gibbus is harvested com-
mercially off the south Atlantic coast of the United States,
and in the northeastern Gulf of Mexico (Allen and Costello
1972). This species is subject to large yearly fluctuations in
stock availability which are related to spawning success.
Spawning is influenced by water temperature changes. In
this paper we determine the spawning season of the calico
scallop on the Florida-Hatteras Shelf off Cape Canaveral,
Florida, and relate spawning to bottom water temperatures
recorded in that area.

A brief summary of calico scallop biology follows. The
calico scallop occurs in depths from less than 2 m to
370 m (Allen and Costello 1972). The species is herma-
phroditic, extruding sperm and eggs for external fertili-
zation; planktonic larvae set in about 16 days (Costello et al.
1973). Young scallops are strongly attached by byssal
threads until about \ x h months after being spawned; older
individuals may be weakly attached (Allen 1979). Growth
is rapid, and scallops reach 55.0 mm shell height in about
9 months (Miller and Hudson, in preparation). (Shell height
is a straight line measurement of the greatest distance
between the umbo and ventral margin.)

Calico scallops are most abundant near coastal promin-
ences such as Cape Canaveral and Cape San Bias, Florida,
and Cape Lookout, North Carolina (Allen and Costello
1972). These concentrations indicate that environmental
conditions near capes contribute to spawning success. Bullis
and Cummins (1961) suggested that "the interruption and
eddying caused by the Cape Canaveral projection probably
permits repetitive settling of scallop larvae." Allen (1979)

Contribution Number 80-57M, Southeast Fisheries Center, National
Marine Fisheries Service, NOAA, Miami, FL 33149.

suggested that current reversals and convergence in the
Cape Canaveral areas as reported by Bumpus (1973), could
"retain scallop larvae on the grounds until settling occurs."
From measurements of bottom current, Leming (1979)
determined that the water flow was cyclic and capable of
maintaining larval calico scallops on the Cape Canaveral
grounds during their 16-day planktonic existence. Further-
more, upwelling near Cape Canaveral, Cape San Bias, and
Cape Lookout may increase the abundance of plankton,
which serves as food for the calico scallop (Allen and
Costello 1972).

METHODS

Bottom water temperatures off Cape Canaveral were
obtained from continuous recording thermographs operated
concurrently with biological studies on the calico scallop
conducted by the Bureau of Commercial Fisheries (now the
National Marine Fisheries Service), Miami, Florida. Temper-
atures were recorded at Buoy 1, located 9 km from land,
depth 18 m (latitude 28°48.5'N, longitude 80°38.6'W), and
at Buoy 2, located 22 km from land, depth 22 m (latitude
28°49.1N, longitude 80°29.0'W) (Figure 1). Except when
a thermograph was lost or malfunctioned, the daily bottom
water mean temperatures at either Buoy 1 or Buoy 2 are
available for most of the period from March 28, 1970 to
August 24, 1971 (Figure 2).

DETERMINATION OF SCALLOP SPAWNING SEASON

Spawning periods of the calico scallop were determined
from biological studies of ovarian developmental stages,
spat abundance, length-frequency distributions, and fish
predation on juvenile scallops. These studies are cited below.

17

18

Miller et al.

28°S0-

28 40-

28 30-

28 20-

80° SO' 80° 40' 80° 30' 80* 20' W

Figure 1. Locations of Buoys 1 and 2 off Cape Canaveral, Florida.

Ovarian Developmental Stages

Roe et al. (1971) used ovarian color to determine the
degree of calico scallop maturation. Based on studies in
1967 and 1968, they concluded that the spawning period
of the calico scallop on the Cape Canaveral grounds "begins
in late February or March and continues to June" but
"protracted spawning" occurs in some areas.

The developmental stages of calico scallop ovaries from
the Cape Canaveral grounds were distinguished, primarily
by color, from May 1970 to October 1971 by Miller et al.

( 1 980). The spawning period was indicated by the occurrence
of ripe and partially spawned scallop ovaries. According to
Miller et al. (1980), "spawning intensity was apparently
highest from January to May, decreased in June and July
and was nonexistent in August and perhaps in September.
In October, a high proportion of scallops was close to
spawning condition. By November, spawning had apparently
begun . . . and probably increased in December."

Spat A bundance

Calico scallop spat were monitored off Cape Canaveral
by means of spat traps (Allen 1979). Based on seasonal
abundance of spat from July 1970 to October 1971, Allen
determined that "spawning apparently occurred during all
seasons of the year, but intensity was greatest in the spring.
Following low spawning intensity in July, and lower
intensity from August into December, spawning increased
in late December or January and peaked in March. High
spawning intensity continued through April and May,
followed by an abrupt decrease in June and low spawning
intensity into September."

Length- Frequency Distributions

Length frequencies of calico scallops were obtained off
Cape Canaveral from a bed at Buoy 2 from March 1970 to
October 1971 (Miller and Hudson, in preparation). These
length frequences (supported by data from marked scallops)
showed major recruitment of age class scallops occurred
between December and June, indicating that major spawning
occurred from about December to May.

Predation on Juvenile Scallops

Spawning season of the calico scallop also can be esti-
mated from food habits of predators. A study of food

DAILY MEAN TEMPERATURE, BUOY 1
DAILY MEAN TEMPERATURE. BUOY 2

' Fll ' a«R ' an ' aw ' JME ' JULY ' tut
1971

Figure 2. Bottom water temperatures at Buoys 1 and 2 off Cape Canaveral, Florida, 1970-71 (from data presented by Leming 1979).

Spawning of Calico Scallop

19

habits of a batfish, Ogcocephalus sp., was conducted on
specimens obtained off Cape Canaveral in 1974 (Winans
1976). The batfish consumed mostly scallops from Decem-
ber through June, and mostly gastropods from July through
November. Although Winans (1976) did not identify the
scallops as to species, the calico scallop is the predominant
species off Cape Canaveral, constituting more than 99% of
the identifiable spat caught in traps (Allen 1979). The bat-
fish has a very small mouth, and we speculate that the
maximum size of scallops consumed would not exceed
15 mm shell height. Calico scallops of 15 mm shell height
are estimated to be about 54 days after spawning (Allen
1979). Based on these scallop ages, and the season of
maximum predation (December through June), indications
are that most calico scallop spawning occurred between
November and May.

SCALLOP SPAWNING IN RELATION TO BOTTOM
WATER TEMPERATURE REGIME

Range and fluctuations of bottom water temperatures
are critical to the spawning of the bay scallop Argopecten
irradians, and the closely related calico scallop. The bay
scallop spawns naturally in mid-summer in Massachusetts
when water temperatures rise above 16.4°C (Belding 1910).
However, bay scallops spawn during declining temperatures
of late summer and fall in North Carolina (Gutsell 1931)
and in Florida (Sastry 1963). In the laboratory, bay scallops
spawned only after the temperature was increased and then
decreased (Gutsell 1931, Sastry 1963, Castagna 1975).
Calico scallops were induced to spawn in the laboratory by
raising the water temperature from 20° to 25°C (Costello
et al. 1973). These temperatures, however, represent only
part of the range within which calico scallops will spawn.

An understanding of calico scallop spawning off Cape
Canaveral as affected by temperature first requires knowl-
edge of scallop distribution as related to depth and temper-
ature. Concentrations of calico scallops off Cape Canaveral
are between depths of 18 and 55 m and, therefore, are
within an environmental zone designated as the "Open-
Shelf Habitat" by Struhsaker (1969). Bottom water tem-
peratures in this zone range from about 11° to 27°C,
and are warmer in the-winter and cooler in the summer than
those temperatures in the coastal zone, which extends out
from shore to about 18 m (Struhsaker 1969). Mathews and
Pashuk (1977), and Leming (1979) further indicate that
waters deeper than about 55 m are cooler year-round than
waters in the 18- to 55-m depths. Based on bottom water
temperatures associated with the calico scallop, this species
is classified as subtropical tolerant (Miller and Richards
1980). For this reason, temperatures colder than 15°C and
warmer than 27°C may be lethal to the major portion of
the calico scallop population, and may establish the mini-
mum and maximum depth distributions of scallops on the
shelf. Therefore, the calico scallop, with its distribution
controlled by temperature requirements, is restricted to

a well-defined depth range off Cape Canaveral, with the
largest numbers of heavy concentrations in 33 to 42 m
(Miller and Richards 1980).

Based on biological observations reported here for several
different years, 1967 to 1968, 1970 to 1971, and 1974,
most spawning of calico scallops off Cape Canaveral gener-
ally occurs between November and June, but not necessarily
during all of those months each year. We believe that
seasonal variations in the annual spawning pattern can be
attributed to variations in the annual bottom water temper-
ature cycle. In 1970 and 1971, spawning intensity deter-
mined from ovarian developmental stages, scallop spat
abundance, and scallop length-frequency distributions,
apparently was highest from January to May and lowest
from June to October.

Spawning intensity in 1970 and 1971 can be correlated
with bottom water temperatures recorded at Buoys 1 and 2
(Figure 2). Low spawning intensity occurred from June to
October, when temperatures usually were above 22.5°C.
High spawning intensity occurred from January to May
when temperatures were below 22.5°C. From November
through May, there were more than five rapid major fluctu-
ations (4°C or more) in bottom water temperature. During
this period, calico scallops apparently spawned intermittently
as indicated by the repeated high percentage of ripe scallop
ovaries (Miller et al. 1980), and the continued recruitment
of age class scallops (Miller and Hudson, in preparation).

In determining the temperature range for spawning of
the calico scallop, we recognized that the heaviest concen-
trations of scallops off Cape Canaveral occurred in depths
of 33 to 42 m. Therefore, most of the scallop concentra-
tions were deeper than the 18 and 22 m depths where
bottom water temperatures were recorded at Buoys 1 and 2.
Some scallops in depths of 22 m at Buoy 2 were ripe in
November 1970 (Miller et al. 1980). Based on the annual
cycle of bottom water temperatures, these scallops were
subjected to declining temperatures below 22.5°C beginning
in late November 1970 (Figure 2). These declining water
temperatures, a direct result of seasonal atmospheric cooling,
apparently initiated limited spawning at Buoy 2 in late fall
and early winter.

Records of bottom water temperatures deeper than 22 m
off Cape Canaveral were inadequate for refined analysis,
since they were only available from expendable bathy-
thermograph records taken at intervals of about VA months
from January to December 1971 (Leming 1979). However,
temperatures associated with the heaviest concentrations of
scallops (at 33 to 42 m) probably did not decline below
22.5°C until January 1971. The records (Figure 2; Leming
1979) suggest that during the major spawning season,
January to May, bottom water temperatures at depths from
18 to 55 m ranged from about 15.0° to 22.5°C. As shown
by Leming (1979), in January the 18°C isotherm inter-
sected the bottom shoreward of the 55-m depth contour.
Beginning in March, cold (18°C) bottom water, cooled by

20

Miller et al.

intrusions, moved onshore from the outer shelf. As this water
progressed onshore, it "passed over the concentrations of
scallops expected to be mostly ripe during March, April, and
May and perhaps triggered successive spawning" (Allen 1979).
By June, the 18°C isotherm had extended shoreward to the
18-m depth curve, and the 15°C isotherm to the 55-m curve
(Leming 1979). Intrusions occurring in August did not cause
spawning because scallop ovaries either were spent, immature
or developing (Miller et al. 1980).

In summary, major spawning of calico scallops on the
Cape Canaveral grounds in 1970 and 1971 occurred from
January to May when bottom water temperatures were
between 15.0° and 22.5°C.

COLD WATER INTRUSIONS

Along the southern Atlantic and northeastern Gulf of
Mexico coasts of the United States, cold water intrusions
that create temperature anomalies in nearshore waters have
been documented near Cape Canaveral (Taylor and Stewart
1959), and Cape Lookout (Wells and Gray 1960). Intrusions
are not restricted to shelf areas near coastal prominences, but
they may not commonly move across the entire shelf to shore
in all areas. Near Cape San 31as and Cape Lookout, intrusions
apparently contribute to the formation of bottom water
temperature patterns similar to those off Cape Canaveral.

Factors controlling the annual bottom water tempera-
ture regime off Cape Canaveral were reviewed by Leming
(1979). Seasonal warm or cold atmospheric temperatures
have strong influences on bottom water temperatures,
affecting initially those on the western or inshore border
of the calico scallop zone. However, intrusions of deep,
cold water onto the Florida-Hatteras Shelf influence initially
the eastern or offshore border of the calico scallop zone.
According to Atkinson et al. (1978), intrusions "can be
forced by wind, eddies, meanders, or density motions."

Cold water intrusions had the following effects off Cape
Canaveral. The offshore bottom water, repeatedly cooled
by intrusions in late winter, spring, and summer, caused the
18°C isotherm to progress shoreward on the shelf (Leming
1979). In late June and July 1971, the mean bottom
temperatures increased shoreward from 16.6°C at Leming's
temporary offshore station, CM2, depth 60 m, to 22.3°C
at the inshore station. Buoy 1, depth 18 m (Table 1). The
range in temperature was the largest at CM2, 9.4°C,
decreasing shoreward to Buoy 1, 3.8°C. Rapid decreases in
temperatures occurred: at CM2 temperatures decreased
5.3°C in 4 days; while at Buoy 1 temperatures decreased
3.4°C in 3 days. Leming (1974) showed there was an 8- to
9-day lag in temperature between CM2 and Buoy 1 due to
intrusions. It is assumed that the subtropical tolerant calico
scallop could not survive at CM2 as the bottom temperature
was below 15°C for three consecutive days, reaching a low
of 12°C for 2 days at this location.

Intrusions of cold water on the shelf may be favorable
or unfavorable to the calico scallop. Intrusions may be
favorable when they (l)initiate scallop spawningby lowering

TABLE 1.

Daily mean bottom water temperatures off Cape Canaveral, Florida,
June 26 to July 23, 1971 (from Leming 1979).

Station and Water Depth

CM2

Buoy 2

Buoy 1

Date

60 m

22 m

18 m

Temperature

'c

June 26

15.8

21.7

-

27

16.0

19.8

21.5

28

17.1

19.5

21.1

29

18.7

19.5

22.4

30

18.0

19.8

23.1

July 1

16.1

19.9

23.1

2

15.5

19.9

22.5

3

14.4

19.3

21.5

4

15.5

19.0

23.8

5

16.4

20.6

24.3

6

15.7

22.5

24.3

7

16.6

22.8

24.3

8

18.0

22.9

24.1

9

17.7

22.3

23.9

10

18.1

21.1

23.2

11

21.1

20.5

21.6

12

21.4

19.4

20.5

13

19.6

20.5

20.8

14

18.3

20.6

21.7

15

16.1

19.5

21.7

16

15.4

19.8

21.9

17

14.5

19.8

21.7

18

15.1

19.8

21.4

19

15.6

20.2

21.5

20

12.6

20.9

22.5

21

12.0

19.7

21.6

22

14.5

17.4

21.1

23

18.2

16.8

21.7

Minimum and maximum C

12.0-21.4

16.8-22.9

20.5-24.3

Mean temperature

16.6

20.2

22.3

Range

9.4

6.1

3.8

the water temperature below 22.5°C; (2) transport nutrient-
rich water shoreward (Atkinson et al. 1978), producing
phytoplankton blooms as food for scallops; and (3) lower
the bottom water temperature to a range within which the
calico scallop can survive, about 15.0° to 27.0°C. Intrusions
may be unfavorable when they lower the bottom water
temperatures below the minimum tolerance level of the
calico scallop, 15°C, causing mortalities of larvae, spat,
juveniles, and adults. Thus, the distance these cold intru-
sions extend shoreward controls the outer limits of the
calico scallop grounds and affects the magnitude of the
stock.

Measurements of bottom water temperatures, monitored
by thermograph arrays in depths from 18 to 110 m, may be
useful in prediction of spawning success and survival of
the calico scallop and, therefore, estimation of the size
of the annual crop.

Spawning of Calico Scallop

21

REFERENCES CITED

Allen, D. M. 1979. Biological aspectsof the calico scallop, Argopecten
gihbus, determined by spat monitoring. The Nautilus 93:
107-119.

& T. J. Costello. 1972. The calico scallop, Argopecten

gibbus. NOAA Tech. Rep. Nat. Mar. Fish. Serv. Spec. Sci. Rep.
Fish. 656. 19 pp.

Atkinson, L. P., G.-A. Paffenhoffer & W. M. Dunstan. 1978. The
chemical and biological effect of a Gulf Stream intrusion off
St. Augustine, Florida. Bull. Mar. Sci. 28:667-679.

Belding, D. L. 1910. A Report upon the Scallop Fishery of Massachu-
setts. Including the Habits. Life History of Pecten irradians, its
Rate of Growth, and Other Facts of Economic Value. Wright &
Potter Printing Co., Boston. 150 pp.

Bullis, H. R., Jr. & R. Cummins, Jr. 1961. An interim report of the
Cape Canaveral calico scallop bed. Commer. Fish. Rev. 23(10):
1-8.

Bumpus, D. F. 1973. A description of the circulation on the Conti-
nental Shelf of the east coast of the United States. Pages 111-
157 in B. A. Warren (ed.), Progress in Oceanography. Vol. 6.
Pergamon Press, New York.

Castagna, M. 1975. Culture of the bay scallop, Argopecten irradians.
in Virginia. Mar. Fish. Rev. 37(1): 19-24.

Costello, T. J., J. H. Hudson. J. L. Dupuy & S. Rivkin. 1973.
Larval culture of the calico scallop, Argopecten gibbus. Proc. Nat.
Shellfish. Assoc. 63:72-76.

Gaul, R. D., R. E. Boykin & D. E. Letzring. 1966. Northeast Gulf of
Mexico hydrographic survey data collected in 1965. Texas A&M
University, Department of Oceanography, Proj. 286-D, Ref.
66-8T. 202 pp.

Gutsell, J. S. 1931. Natural history of the bay scallop. Bull. U.S.
Bur. Fish. (1930) 46:569-632.

Leming, T. D. 1979. Observations of temperature, current, and wind

variations off the central eastern coast of Florida during 1970

and 1971. NOAA Tech. Mem. Nat. Mar. Fish. Serv. SEFC. 6.

172 pp.
Mathews, T. D. & O. Pashuk. 1977. A description of oceanographic

conditions off the southeastern United States during 1973.

South Carolina Mar. Resour. Cent. Tech. Rep. 19. 105 pp.
Miller, G. C, D. M. Allen, T. J. Costello & J. H. Hudson. 1980.

Maturation of the calico scallop, Argopecten gibbus. determined

by ovarian color changes. Northeast Gulf Sci. 3:96-103.
Miller, G. C. & J. H. Hudson. Age and growth of the calico scallop,

Argopecten gibbus. Nat. Mar. Fish. Serv., Southeast Fish. Ctr.,

Miami, F'L (in preparation).
Miller, G. C. & W. J. Richards. 1980. Reef fish habitat, faunal

assemblages, and factors determining distributions in the South

Atlantic Bight. Pages 114-130 in Proc. Gulf Caribb. Fish. Inst.

32nd Annual Session.
Roe, R. B., R. Cummins, Jr. & H. R. Bullis, Jr. 1971. Calico scallop

distribution, abundance, and yield off eastern Florida, 1967-

1968. Fish. Bull.. U.S. 69:399-409.
Sastry, A. N. 1963. Reproduction of the bay scallop, Aequipecten

irradians Lamarck. Influence of temperature on maturation and

spawning. Biol. Bull. (Woods Hole) 125:146-153.
Struhsaker, P. 1969. Demersal fish resources: composition, distri-
bution, and commercial potential of the Continental Shelf stocks

off southeastern United States. Fish. Ind. Res. 4:261 -300.
Taylor, C. B. & H. B. Stewart, Jr. 1959. Summer upwelling along

the east coast of Florida. J. Geophys. Res. 64:33-40.
Wells, H. W. & I. E. Gray. 1960. Summer upwelling off the northeast

coast of North Carolina. Limnol. Oceanogr. 5:108-109.
Winans, G. 1976. Food habits of two sympatric batfishes (Ogco-

cephalidae) offshore of Cape Canaveral, Florida. Pacific Sci.

30:215 (abstract).

Journal of Shellfish Research, Vol. 1, No. 1. 23-32, 1981.

REPRODUCTIVE CYCLES OF THE ATLANTIC SURF CLAM SPISULA SOLIDISSIMA,
AND THE OCEAN QU AHOG ARCTICA ISLANDICA OFF NEW JERSEY

DOUGLAS S. JONES

Department of Geology,
University of Florida,
Gainesville, Florida 32611

ABSTRACT Annual reproductive cycles of two commercially important bivalves, the Atlantic surf clam Spisula
solidissima and the ocean quahog Arctica islandica, were investigated using specimens collected off the New lersey coast.
Specimens of both species were recovered from commercial port landings during two consecutive years, April 1977 through
March 1979. Gonadal tissues were prepared by standard histological techniques for a microscopic examination of seasonal
gametogenesis, and for determination of time and duration of spawning.

Gametogenesis in inshore surf clams proceeded slowly over the winter months, but by late May or June, the gonads were
characterized by an abundance of morphologically ripe eggs or sperm. Partially spawned individuals were first encountered
in June or July; their abundance rose sharply in late summer-fall when spawning was heaviest. All were spent by November
or December.

A similar pattern of gametogenic development was observed in the ocean quahog. All gonads contained morphologically
ripe eggs or sperm by August. However, spawning activity in this species was highest in the fall and often persisted into the
winter months, particularly in 1978-1979.

Temporal differences between reproductive cycles of consecutive years may be related to differences in environmental
factors. Comparison of results obtained here with previously published studies revealed important similarities and differences.

INTRODUCTION

The Atlantic surf clam Spisula solidissima (Dillwyn) and
the ocean quahog Arctica (= Cyprina) islandica Linne are
two of the largest and most abundant bivalve species inhab-
iting marine waters of northeastern United States. Spisula
solidissima lives in a zone from the shallowest subtidal out
to depths of about 60 m. It is found from the Gulf of St.
Lawrence, Canada, south to Cape Hatteras, North Carolina
(Merrill and Ropes 1969, Ropes 1980). Arctica islandica
overlaps the latitudinal range of the surf clam but has a
more extensive distribution from Cape Hatteras northward
to the southern coast of Newfoundland, around Iceland,
and along the coast of Europe (Nicol 1951, Ropes 1979).
Ocean quahogs most commonly occur farther offshore than
surf clams, though overlapping of both species occurs and
is most pronounced between depths of 18 to 55 m (Ropes
1979).

Both species are of great commercial importance. Surf
clams have been heavily fished since the late 1940's; landings
reached a peak of 96 million pounds in 1974 (Serchuk et al.
1979). Overfishing led to severe reductions in landings
which dropped to 49 million pounds in 1976 (Serchuk et al.
1979). The decline in surf clam densities in the overfished
beds prompted the shellfish industry to begin intensive
harvesting of the ocean quahog in 1975-1976 (Ropes 1979).
A management plan for both species, which included
research on their biology and ecology, was initiated in 1977
by the Mid-Atlantic Regional Fisheries Council (Ropes
1979). Since both of these species are of economic signifi-
cance, it is important to know as much about their life
histories, including reproduction, as possible.

A unique opportunity to examine the reproductive cycles
of surf clams and ocean quahogs from New Jersey for a

continuous 2-year period arose in 1977. Specimens of
each species were collected at regular intervals to study the
annual cycle of shell formation (Jones 1980). At the same
time, gonadal tissues of each clam were recovered. Analysis
of this gonadal material provided comparative data on
seasonal gametogenesis, and on times and duration of
spawning for the two species.

Early attempts to document the reproductive cycle of
surf clams using gonad distension (Westman and Bidwell
1946), and excision of gametes (Allen 1951, 1953; Schecter
1941) were followed by Ropes (1968), whose histological
examination of gonads of New Jersey surf clams over a
3^-year period represents the most comprehensive study to
date. Ropes (1968) used offshore surf clams, collected at
depths of 18 to 32 m, living below the thermocline. Speci-
mens used in the present study came from shallower, more
inshore habitats, and they probably lived above the thermo-
cline (based on hydrographic summaries by Bigelow [1933]
and Bowman [1977] ).

Loosanoff (1953) gave a detailed account of the repro-
ductive cycle in ocean quahogs using specimens from Point
Judith, Rhode Island. He examined 162 individuals during
two thirds of one year (from March 22 to November 1).
Other studies of the reproductive cycle of A. islandica in
the Baltic Sea by Jaeckel (1952) and by von Oertzen (1972)
are more qualitative and fragmentary. The present study,
using twice as many specimens as Loosanoff ( 1953), reports
the reproductive cycle of ocean quahogs in New Jersey
waters during a 2-year period, thus representing the most
complete study to date.

MATERIALS AND METHODS

All clams were collected from commercial port landings

23

24

Jones

between April 11, 1977 and March 15, 1979. Ten specimens
of each species were taken at biweekly intervals in the spring,
summer, and fall, and at monthly intervals during the winter.
In all cases the clams were shucked and prepared within
2 hours after being obtained.

Ocean quahogs came predominantly from an offshore
Asbury Park, New Jersey, location (40°15'N, 73°40'W;
25 to 32 m water depth), though some samples (April 1977,
June 1978, February and March 1978) were collected from
offshore Cape May, New Jersey (38°55'N, 74°25'W; 25 to
27 m water depth). A total of 320 ocean quahogs with
shell lengths ranging from 58 to 125 mm were analyzed.

Most surf clams were harvested from inshore beds along
Island Beach, between Pt. Pleasant , New Jersey , and Barnegat
Inlet. Specimens lived within 1.5 km from shore at depths
of 6 to 10 m. Samples for January, February, and March
1979, came from similar depths off Wildwood Beach. Shell
lengths of the 350 surf clams analyzed ranged from 75 to
164 mm.

The entire visceral mass of each clam was held for 48 hours
in Davidson's fixative. Tissues were then transferred to 70%
ETOH. In preparing slides for microscopic examination,
tissues containing gonad ventral to the heart were cut from
each specimen, dehydrated, and infiltrated with paraffin.
Sections, 5 jum thick, were cut and stained with Harris
hematoxylin and eosin Y (Preece 1972). Serial sectioning
of several individuals revealed some sequential gonadal
development. Therefore, to minimize variability between
samples, sections were cut from the central portion of the
gonad ventral to the heart, which seemed to be most repre-
sentative of the bulk of the gonad.

Microscopic examinations of each section permitted
assigning each specimen to a category of gonad develop-
ment following those described by Ropes (1968): early
active (EA), late active (LA), ripe (R), partially spawned (PS),
and spent (S). These are divisions of convenience in a con-
tinuum; boundaries between phases are not sharp. Detailed
descriptions of the histological characteristics of male and
female surf clams in each of these phases can be found in
Ropes (1968). Gametogenesis in ocean quahogs, described
in detail by Loosanoff (1953), is similar to that of surf clams,
so the same categories were applicable and detailed descrip-
tions need not be repeated. Proportions of clams in each
category were recorded and grouped by months to analyze
the temporal progression of the reproductive cycles. Speci-
mens, borderline between two successive phases, were
counted as 50% in each phase. Photomicrographs of typical
successive phases in male and female gonadal tissues of both
species are shown in Figures 1 through 4.

Monthly sea surface temperatures for the collection dates
and the localities of inshore surf clams living above the
thermocline were assembled from the National Weather
Records Center in Asheville, North Carolina, and from
Gulfstream, published by the U.S. Department of Commerce,
National Oceanic and Atmospheric Administration. Bottom

temperatures, for the localities where ocean quahogs were
collected, were estimated from the summaries of Walford
and Wickland (1968), Colton and Stoddard (1973), and
Bowman (1977).

RESULTS

Spisula solidissima (Figure 5)

In April 1977, 5% of the surf clam population were in the
early active phase of development, 85% were late active,
and 10% were ripe. Ripening continued throughout May
and June; by the end of June some clams had begun to
spawn. A small percentage of partially spawned individuals
was encountered throughout the summer months; September
through November, all of the specimens were either partially
spawned or spent. In December, only 10% of the surf
clams appeared partially spawned, while 90% were spent.
Lumina of the gonadal alveoli in spent clams were devoid of
ripe spermatocytes or oocytes, but the already thickening
alveolar walls contained gonia in the early stages of gameto-
genesis. By January, 80% of the gonads were in the early
active phase and, by February, all clams were early active.
About 20%. reached the late active stage by March.

The pattern of the reproductive cycle in the following
year was not greatly different. By April 1978, 70% of the
surf clams had developed to the late active phase and, by
May, 85% were late active. Though coming one month
later than in 1977, ripening proceeded rapidly; by June, 75%
of the surf clams sampled were ripe. Some partially spawned
clams appeared in the following months, and the percentage
of ripe individuals declined. Partially spawned clams domin-
ated the September and October samples, accounting for
90% of the population by the end of October. The spawning
cycle was completed in November when every specimen
was categorized as spent. Similar gametogenic developments
completed the cycle during the month of December in the
previous year. In succeeding months, the number of individ-
uals in the early active phase rose dramatically. By March
1979, 55% were in the early active stage, whereas 45% had
already achieved the late active condition.

Of the 350 surf clams examined, 176 (50.3%) were males
and 174 (49 .7%) were females. The sex ratio was thus deter-
mined to be 1:1. The sexes were clearly separate; no
hermaphrodites were encountered.

Arctica islandica (Figure 6)

The reproductive cycle of Arctica islandica also varied
between the two years in which it was examined. The
months of April through August were similar with gonadal
ripening proceeding evenly; by August of 1977 and 1978,
90 to 100% of the clams were ripe. Thereafter, there were
larger discrepancies between the two years. Partially spawned
(65%) and spent (20%) clams comprised the bulk of the
sample population in September 1977. whereas in September
1978, 100% of the population were still in the ripe phase.

Reproductive Cycles oi- Surf Clams and Ocean Quahogs

25

Spawning activity continued vigorously through October
1977 and into November when, by the end of the month,
95% of the clams were spent. In contrast, partially spawned
clams were not detected in 1978 until October, and a signif-
icant number of ripe specimens persisted until January. The
principal months of spawning during the second year of
investigation were November, December, and January, when
both partially spawned and spent individuals predominated.

As indicated in Figure 6, the gametogenic portion of the
reproductive cycle began earlier in the first year when all
clams were in the early active phase by December 1978.
Thereafter, more clams developed to the late active phase.
No early active quahogs were detected during the second
year until January 1979, and it was not until February that
90% were in the early active phase. This was about 2 months
later than the preceeding year. As with the surf clam, it
should be pointed out that the ocean quahog exhibited no
"indifferent period" when the gonadal alveoli were totally
free of germinal cells. Even in spent individuals, the early
germinal cells of garnet ogenesis were evident in the thickened
alveolar walls.

Of the 320 ocean quahog gonads examined in this study,
186 (58%) were males and 134 (42%) were females. To
check the hypothesis that the sex ratio was 1:1 as in the
surf clam, 1 used a two-sided test based on the normal
approximation to the binomial distribution. The observed
proportion was significantly different from the hypothesized
value of 50% (P = 0.008). Sex ratio for ocean quahogs was
not reported by previous workers (i.e., Loosanoff 1953,
von Oertzen 1972, Landers 1976, Thompson et al. 1980).
As with the surf clam, sexes were clearly separate; no
hermaphrodites were encountered.

DISCUSSION

Spisula sotidissima

Ropes (1968) observed a biannual reproductive cycle in
gonads of surf clams during 3 of the 4 years in which he
sampled from below the thermocline in offshore New Jersey.
He found the biannual cycle was characterized by a major
mid-year spawning, and by a minor late-year spawning,
but allowed that the second cycle may not be an annual
event.

Results reported in this investigation (Figure 5) of inshore
surf clams living just above the summer thermocline are very
similar to those of Ropes (1968) for the half year, January
to June. Each year, this period was characterized by 90 to
100% of the surf clams in the early active phase in January,
maturing to the ripe phase by June. During the remaining
months (July though December), the two investigations
report very different frequencies of individuals in each
phase. In the years 1962, 1963, and 1964, Ropes (1968)
reported two spawnings— a major mid-year event during
July/ August, and a second minor spawning during October/
November. However, in 1965, when temperatures were

considerably lower than in previous years. Ropes found
only one spawning event, delayed and longer lasting than in
the previous years.

As indicated in Figure 5, the results of this investigation
suggest only one spawning period for inshore surf clams.
While partially spawned individuals were encountered
occasionally in June, they did not appear in high percentages
until late summer. The bulk of spawning activity was
concentrated in August through October and often into
early November. By late November or December, all gonads
appeared spent and the spawning phase was completed.
Renewed gametogenic activities were already evident in the
alveolar walls of the flaccid gonads.

Without adequate environmental data collected concur-
rently with the surf clams, hypotheses concerning the influ-
ence of environmental factors (e.g., temperature) upon the
temporal progression of the reproductive cycle seem unwar-
ranted. Also, with only 2 years of data it was impossible to
ascertain which year was more typical. Certain generaliza-
tions can, however, be made: (1) inshore surf clams did not
appear to undergo two spawning events as Ropes (1968)
described for offshore clams from New Jersey; (2) spawning
occurred most heavily in late summer and fall when water
temperatures were highest; and (3) the rate of gametogenic
development, gonadal ripening, and initiation and duration
of spawning varied somewhat from year to year, probably
in response to environmental factors.

Arctica islandica

All previous investigators reported roughly the same
sequence of gametogenic events in the ocean quahog:
(1) unripe oocytes and spermatocytes were present through-
out the winter, (2) followed by gradual ripening of the
gonads during spring and summer, and (3) spawning in
summer or early fall. However, the timing of these events
varied considerably, apparently depending on geography
and oceanography. Loosanoffs (1953) observations on
samples from Rhode Island were similar to some of those
obtained here, particularly in the first year (1977—1978)
of the study. Results of the second year of my investigation,
however, indicated that spawning may be delayed well into
the fall or winter months. In contrast, von Oertzen (1972)
concluded the spawning period in samples from the Bay of
Mecklenburg (Baltic Sea) extended from May to September.
This was earlier (by 2 to 3 months) than was observed in
the western North Atlantic, but the spawning duration
(4 to 5 months) was approximately the same. It is interesting
to note that Jaeckel (1952), working in the Bay of Lubeck,
also in the Baltic Sea, reported the spawning period of
Arctica commenced in July and proceeded for some
undetermined months thereafter, a result more consistent
with those from North America.

As with the surf clam, concurrent environmental data
were not collected with the ocean quahogs because the
specimens were obtained from commercial clammers.

26

Jones

££*tt£3*g" a»«^^*;^Wjj

E

mi vr

Spisula
solidissima

Male
Gonads

0.1 mm

Figure 1. Sections of gonadal tissue from male surf clams Spisula solidissima in each phase of the
reproductive cycle. A. Early active phase (E A)— thickened alveolar walls with spermatogonia, primary
spermatocytes proliferating into lumen. B. Late active phase (LA)-secondary spermatocytes abundant,
spermatids massing in lumen. C. Ripe phase (R)— mature sperm form dense, swirling masses in alveoli.
D. Partially spawned phase (PS)-ripe sperm less dense than in previous phase, spermatogonia developing
in alveolar walls. E. Spent phase (S)-lumina devoid of sperm, primary spermatogonia developing in
thickening alveolar walls.

REPRODUCTIVE CYCLES 01 SURI CLAMS AND OCLAN QUAHOGS

27

o.

Female
Gonads

Spisula
solidissima

™ : ' v •" * -i '.

Figure 2. Sections of gonadal tissue from female surf clams Spisula solidissima in each phase of the
reproductive cycle. A. Early active phase (EA)-oogonia embedded in alveolar walls while early oocytes
remain attached to basement membrane. B. Late active phase (LA)-enlarging oocytes fill lumina, some
are unattached while others remain attached. C. Ripe phase (R)-large, rounded, ripe oocytes are free in
the lumina. D. Partially spawned phase (PS)-significantly less ripe oocytes in lumina than in previous
phase, some lumina barren, gonad appears flaccid. E. Spent phase (S)-Iumina of alveoli devoid of ripe
oocytes, thickening walls contain developing oogonia.

0.1 m

m

28

JONES

Arctica
islandica

0.1 mm

v>»;

Figure 3. Sections of gonadal (issue from male ocean qualiogs Arctica islandica in each phase of the
reproductive cycle. A. Early active phase (EA)-spermatogonia developing from thickened alveolar walls.
B. Late active phase (LA)-spermatogonia developing at periphery while ordered packing of spermatozoa
has begun in the lumina. C. Ripe phase (R)-swirling masses of mature sperm fill gonadal alveoli.
D. Partially spawned phase (PS)-ripe sperm much less dense than in previous phase, alveoli no longer
distended. E. Spent phase (S)-lumuia devoid of ripe sperm, spermatogonia developing along liasal
membrane.

Ri PRODUCTivi- Cycles of Surf Clams and Ocean Quahocs

29

• CiB«™A ^""* ' Dl f ' ! j25£ -

w?-»^«*

Arctica
islandica

•i '^*w*P

fig **?*WI $£&

A.

*3 ,# **

'%~'^,

Female
Gonads

0.1 mm

Figure 4. Sections of gonadal tissue from female ocean quahogs Arctica islandica in each phase of the
reproductive cycle. A. Early active phase (EA)-oogonia maturing along periphery of alveoli. B. Late
active phase (LA)-enlarging oocytes filling lumina, most still attached by stalk to basement membrane.
C. Ripe phase (R)-ripe oocytes free in lumina, alveolar walls thin and gonad distended. D. Partially
spawned phase (PS)-few ripe oocytes remain in alveoli, gonad is flaccid. E. Spent phase (S)— lumina
devoid of ripe oocytes, alveolar walls thickening, oogonia developing at periphery.

30

JONES

A M J

MONTHS
A S O

100

YEAR 1 50

100

YEAR 2

AVERAGE

BOTTOM

TEMPERATURE

(°C)

50 %

%

(°C)

1

M

i
J

"T

J

1

A

1 !

s o

MONTHS

i
N

i
O

M

Figure 5. Percentages of inshore surf clams (Spisula solidissima) in each phase of the reproductive cycle during each month of this
2-year study are shown in the top two diagrams. YEAR 1 = April 1977 through March 1978; YEAR 2 = April 1978 through
March 1979. Abbreviations for phases of reproductive cycle are explained in Figures 1 through 4. For comparison, a record of
average monthly mean sea surface temperatures for the same time interval in the region where the surf clams were collected is
included (bottom diagram).

REPRODUCTIVE CYCLES OF SURF CLAMS AND OCEAN QUAHOGS

31

YEAR 1 50--:

$-50 %

A M J JASON

M

100

YEAR 2

•100

-50 %

20

AVERAGE

BOTTOM
TEMPERATURl
(°C)

15

10-

M

—r-
A

~ i —

MONTHS

—r-
S

— T—

N

—r-
D

T"

F

20
15
10

>5

(°C)

M

Figure 6. Percentages of ocean quahogs (Arctica islundica) in each phase of the reproductive cycle during each month of this
2-yeai study are shown in the top two diagrams. YEAR 1 = April 1977 through March 1978; YEAR 2 = April 1978 through
March 1979. Abbreviations for phases of reproductive cycle are explained in Figures 1 through 4. For comparison, a record of
average monthly mean sea surface temperatures for the same time interval in the region where the ocean quahogs were collected
is included (bottom diagram).

32

Jones

Therefore, it was not possible to interpret accurately the
events of the reproductive cycle in terms of environmental
influences. Some useful observations may nevertheless be
gleaned from the data: (1) in consecutive years, rate of
gonadal ripening, and the initiation and duration of spawning
may vary, probably in response to environmental factors;
(2) spawning off New Jersey appeared to be an autumnal
to early winter event rather than summer/early autumn as
previous studies suggested; and (3) comparison of gonadal
observations with average bottom temperatures for the area
of collection (Figure 6) suggested that initiation of spawning
was coincident with highest bottom water temperatures.
Loosanoff (1953) concluded that spawning began when
water temperatures reached ~ 13.5°C. This was consistent
with the present study. It should be emphasized, however,
that monitoring of bottom temperatures was not a part of
either study. In both cases, temperatures were estimated
from published summaries.

ACKNOWLEDGM ENTS

1 thank I. Thompson and A. G. Fischer of Princeton
University for their guidance, encouragement, and sugges
tions. For helpful discussions and reviews of the manuscript.
I thank J. Ropes of the National Marine Fisheries Service
and R. Mann of the Woods Hole Oceanographic Institution.
R. Dempsey of Snow Food Products graciously supplied
many of the samples at no charge. I thank Elizabeth Vinson
and Carla Jones for typing. This work was done as partial
fulfillment of the requirements for the Ph.D. at Princeton
University. Support was provided by the U.S. Department
of Commerce, National Oceanic and Atmospheric Admin-
istration Sea Grants 04-6-158-44076 and 04-7-158-
44042, National Science Foundation EAR77-23571. and
a Sigma Xi grant-in-aid of research.

REFERENCES CITED

Allen, R. D. 195 1 . The use of Spisula solidissima eggs in cell research.

J. Cell. Comp. Physiol. 37:504-505.
. 1953. Fertilization and artificial activation in the egg of

the surf-clam, Spisula solidissima. Biol. Bull. (Woods Hole) 105:

213-239.
Bigelow, H. B. 1933. Studies of the waters on the continental shelf.

Cape Cod to Chesapeake Bay. I. The cycle of temperature. Pop.

Phys. Oceanogr. Meteorol. 2 : 1 - 1 35 .
Bowman, M. .1. 1977. Hydrographic properties. MESA New York

Bight Atlas. Monograph 1. New York Sea Grant Institute,

Albany, New York. 78 pp.
Colton, J. R. & R. R. Stoddard. 1973. Bottom-water temperatures

on the continental shelf, Nova Scotia to New Jersey. NOAA

Tech. Rep. NMFS Circ. 376. 55 pp.
Jaeckel, S., jun. 1952. Zur Okologie der Molluskenfauna der west-
lichen Ostsee. Schr. Naturwiss. Ver. Schleswig-Holstein 26:18-50.
Jones, D. S. 1 980. Annual cycle of shell growth increment formation

in two continental shelf bivalves and its paleoecologic significance.

Paleobiology 6:331-340.
Landers, W. S. 1976. Reproduction and early development of the

ocean quahog, Arctica islandica. in the laboratory. Nautilus 90:

88-92.
Loosanoff, V. L. 1953. Reproductive cycle in Cyprina islandica.

Biol. Bull. (Woods Hole) 104:146-155.
Merrill, A. A. & J. W. Ropes. 1969. The general distribution of the surf

clam and ocean quahog. Proc. Nat. Shellfish. Assoc. 59: 40-45.
Nicol, D. 1951. Recent species of the veneroid pelecypod Arctica.

J. Wash. A cad. Sci. 4 1 : 1 04 - 1 06 .
Preece, A. 1972. A Manual for Histologic Technicians. Little, Brown

and Co., Boston, MA. 428 pp.
Ropes, J. W. 1968. Reproductive cycle of the surf clam, Spisula

solidissima. in offshore New Jersey. Biol. Bull. (Woods Hole)

135:349-365.

_ . 1979. Biology and distribution of surf clams (Spisula
solidissima) and ocean quahogs {Arctica islandica) off the north-
east coast of the United States. Pages 47-66 in Proceedings of
Northeast Clawi Industries: Management for the Future. Exten.
Sea Grant Program, University of Massachusetts and Massachusetts
Institute of Technology SP— 112.

. 1980. Biological and fisheries data on the Atlantic surf

clam, Spisula solidissima (Dillwyn). Northeast Fisheries
Center. U.S. Nat. Mar. Fish. Serv. Tech. Rep. Ser. No. 24.
88 pp.

Schecter, V. 1941. Experimental studies upon the egg cells of the
clam, Mactra solidissima . with special reference to longevity. ./.
Exp. Zool. 86:461-477.

Serchuk, F. M., S. A. Murawski, E. M. Henderson, & B. E. Brown.
1979. The population dynamics basis for management of offshore
surf clam populations in the Middle Atlantic. Pages 83-100 in
Proceedings of Northeast Clam Industries: Management for the
Future. Exten. Sea Grant Program, University of Massachusetts
and Massachusetts Institute of Technology SP- 112.

Thompson, I., D. S. Jones, & J. W. Ropes. 1980. Advanced age for
sexual maturity in the ocean quahog .4 rctica islandica (Mollusca:
Bivalvia). Mar. Biol. 57:35-39.

von Oertzen, J. A. 1972. Cycle and rates of reproduction of six
Baltic Sea bivalves of different zoogeographical origin. Mar. Biol.
14:143-149.

Walford. L. A. & R. I. Wickland. 1968. Monthly sea temperature
structure from the Florida Keys to Cape Cod. Serial Atlas of the
Marine Environment, Folio 15. American Geographical Society
of New York, New York. 2 pp., 1 6 plates.

Westman, J. R. & M. H. Bidwell. 1946. The surf clam. Economics
and biology of a New York marine resource, (unpublished)
(Copies available from: Library, National Marine Fisheries Service,
Oxford, MD 21654.)

Journal of Shellfish Research, Vol. 1, No. 1, 33-39, 1981.

DISTRIBUTION AND RELATIVE ABUNDANCE OF THE OCEAN QUAHOG
ARCTICA ISLANDICA IN RHODE ISLAND SOUND AND OFF
MARTHAS VINEYARD, MASSACHUSETTS

MICHAEL J. FOGARTY 1

Rhode Island Department of Environmental Management ,

Division of Fish and Wildlife

150 Fowler Street, Wickford, Rhode Island 02852

ABSTRACT Estimates of minimum biomass (total wet weight and meat weight) were derived for Arctiea islandica in
parts of southern New England. Total harvestable biomass for the survey area was estimated at 1.004 x 10 6 metric tons (mt)
total wet weight, and 1.33 x 10 mt meat weight. Stepwise linear discriminant analysis was used to isolate sediment com-
ponents which contribute to separation of regions of high- and low-ocean quahog densities (arbitrarily assigned values of
>0.75 kg/m and<0.10kg/m total wet weight, respectively). The percentage of four sediment fractions: gravel, coarse
sand, medium sand, silt/clay, and the percentage of shell in the sample were sufficient to significantly (P<0.01) discrim-
inate between the two levels of ocean quahog densities. Size composition data and shell length-meat weight regressions for
three depth intervals within the survey area are presented.

INTRODUCTION

The ocean quahog Arctiea islandica supports a small but
valuable commercial fishery in Rhode Island coastal waters.
Initial exploitation of this resource in the United States was
centered in Rhode Island (Arcisz and Neville 1945); until
1976, the entire United States fishery was based in New
England. Declining yields in the highly exploited surf clam
Spisula solidissima fishery (Serchuk et al. 1979, Ropes 1979)
resulted in a marked increase in exploitation of Arctiea
along the Atlantic coast. The shift in directed effort from
the surf clam to ocean quahog, particularly in the Mid-
Atlantic Bight, resulted in a substantial increase in reported
landings. Total catch in the Fishery Conservation Zone
(FCZ) increased nearly five fold from 1976 to 1978
(Fisheries of the U.S., 1 976- 1978). The Rhode Island
catch in the same period increased 86% from 1 ,446 mt to
2,684 mt (Rhode Island Landings 1976-1978).

Distribution of Arctiea along the northeastern coast of
the United States was examined in research surveys con-
ducted by the National Marine Fisheries Service (NMFS)
and its predecessor, the Bureau of Commercial Fisheries
(Merrill and Ropes 1969, 1970; Parker and McRae 1970;
Ropes 1979). Murawksi and Serchuk (1979a) summarized
and integrated the results of these surveys to provide mini-
mum biomass estimates for the Middle Atlantic (Cape Cod
to Cape Hatteras) region.

The present study was undertaken to determine the dis-
tribution of Arctiea in Rhode Island Sound and off Martha's
Vineyard, Massachusetts, in relation to depth and sediment
type. A quantitative assessment of some of the factors
governing ocean quahog density was deemed important for

Present address: National Marine Fisheries Service, Northeast Fish-
eries Center. Woods Hole, MA 02543.

predictive purposes in identifying potentially exploitable
quahog concentrations. Bearse (1976) reviewed the
known ecological determinants of ocean quahog distribu-
tion. This paper presents information on distribution,
minimum biomass, substrate affinities, size composition,
and length-weight relationships for Arctiea within the
survey area.

MATERIALS AND METHODS

Ocean quahog samples were obtained aboard a chartered
commercial fishing vessel equipped with an hydraulic dredge
with a 1 .52-m blade, and a 3.8-cm spacing between the bars
of the retaining cage. Standard sampling tows were of
4-minute duration at a speed of approximately 2.8 km/hr.
Distance covered by the dredge was determined from
LORAN C coordinates recorded to the nearest 0.1 /isec
at the start and end of each tow. The mean distance covered
was 190.2 m (± standard error [SE] = 5.13), resulting in an
average areal coverage of 289.1 m 2 per standard tow.

A simple random sampling design was employed with
stations selected from a grid interval of 1 .8 x 1 .8 km through-
out the survey area in water depths ranging from 18.2 m to
45 .7 m (Figure 1 ). Stations falling on an untowable bottom
were randomly reassigned to an adjacent site. A total of
191 stations were occupied between June 15. 1978 and
August 3, 1978, and an additional 21 stations were sampled
on March 22, 1979. For comparative purposes, the survey
area was divided into three arbitrary depth intervals (18.3—
27.4, 27.5-36.5, and > 36.6 m).

Survey catch data were analyzed according to Aitchison
(1955) and Pennington (NMFS, Woods Hole Laboratory,
personal communication), a method in which the data are
partitioned into zero and nonzero catch values. The condi-
tional distribution of the nonzero class is assumed to be
lognormal (the A-distribution, Aitchison and Brown 1957).

33

34

FOGARTY

Figure 1. Location of sample sites for Arctica in Rhode Island Sound
and south of Martha's Vineyard, Massachusetts.

An unbiased estimator of the sample mean (Aitchison
1955) is:

C = -exp(y)* m (s 2 /2)

and the variance of the sample mean (Pennington, personal
communication) is given by:

Var(c) = n- : exp(2y)[ I l 1 ^ il (s 2 /2)

m ■
m v m

* (

s 2 )]

where m is the number of nonzero observations, n is the
total number of observations, y and s 2 are the mean and
variance of the log-transformed nonzero observations,
respectively, and

,2i-l

v>

1+-!

1

(n+D

-I

t+ S -.,

j=2nJ(n+l)(n + 3)...(n + 2j-3) J-

fJ

At each station the ocean quahog catch was weighed to
the nearest 0.5 kg. In instances where the catch-per-tow was
high (> 250 kg), two level 35-liter (1 U.S. bushel) containers
of ocean quahogs were weighed to the nearest 0.5 kg, and
the remaining catch recorded in number of 35-liter con-
tainers. Estimates of the total sample weight were then
obtained by expanding the mean of the two weighed samples
to the total number of containers.

A random sample of 100 ocean quahogs was retained
for size frequency analysis at each station where Arctica
were obtained. In instances where the total catch was less
than 100 individuals, the entire catch was measured. A
random subsample of 20 quahogs was selected from the
length-frequency sample for length-weight analysis and
taken to the laboratory for processing. Shell dimensions
were recorded to the nearest millimeter and meat weights
recorded to the nearest 0.5 gram. Regression equations

relating drained meat weight and shell length were fit by
nonlinear least squares using a modified Gauss-Newton
algorithm (Ralston and Jennrich 1978). Comparisons
between regression equations derived for the three depth
intervals were made using Rao's homogeneity X test (Rao
1973, pp. 389-391).

Sediment samples were collected at each station using a
Mann sampler (Krumbein and Pettijohn 1938 ) with a 10.2-cm
opening. The Mann sampler was attached to the hydraulic
dredge and collected the sediment sample simultaneously
with the biological sample. Stations at which residual sedi-
ment in the dredge differed from than in the Mann sampler,
or where substantial quantities of rock and stone were
retained, were not further analyzed. An attempt was also
made to limit analyses to samples from unexploited sites
based on prior knowledge of the fishery. Detailed grain-size
analyses were completed for a total of 127 sediment samples.
The substrate samples were washed, oven dried, disaggre-
gated, and dry sieved. The sieves conformed to the standard
Wentworth mesh dimensions (2.0, 1.0, 0.5, 0.25, 0.125,
0.062, and < 0.062 mm). No attempt was made to further
separate the silt/clay (< 0.062 mm) fraction. Shell particles
in each fraction were weighed separately.

Linear discriminant analysis (Fisher 1936) was used to
differentiate between regions of high- and low-ocean quahog
densities (arbitrarily assigned values of > 0.75 kg/nr and
< 0.10 kg/m 2 , respectively) on the basis of sediment com-
position and water depth. Sediment data were expressed
in the linear Krumbein scale

= -log 2 (d)

where d is the Wentworth particle size diameter in milli-
meters (Krumbein and Pettijohn 1938). Percentage values
were treated with an arcsine transform prior to analysis
(Cassie and Michael 1968).

RESULTS AND DISCUSSION

Minimum Biomass

Minimum biomass estimates (total wet weight and meat
weight) were derived for the entire survey area and at each
depth interval. These estimates must be considered mini-
mum since the dredge is not completely efficient, and the
selection characteristics of the dredge cage prevented the
complete retention of quahogs < 70 mm shell length
(Fogarty 1979).

Ocean quahogs were obtained at 139 (bb r Y) of the
stations sampled. The conditional distribution of the
nonzero densities was approximately lognormal (Figure 2);
therefore, estimation of the sample mean and its variance
using A-distribution theory was considered appropriate.
The estimated mean density (total wet weight) of Arctica
for the entire survey area was 0.377 kg/m 2 (Table 1). No
significant differences (P < 0.05) in quahog density between

Distribution and Abundance of Ocean Quahogs

35

depth intervals were discerned (Kruskal-Wallis test; X2 =
3.61 ,ns [not significant] ). A similar estimate of 0.401 kg/ni 2
can be calculated from Bearse ( 1 976 ) based on grab and
SCUBA samples collected off Rhode Island.

80-1

>-60

o

z

111

D

240-

20-

1 I I 1 1 1 1 1 1 1 1 1 1

2 .4 6 8 1.0 1.2 1.4

DENSITY

1— r— i-^—r

1.6 1.8 2.0 2.2 >Z3

Figure 2. Frequency distribution of untransformed ocean quahog
density (kg/m total weight) and log-transformed nonzero density
values (insert).

Estimates of total wet weight were converted to meat
weight assuming a meat weight:total weight ratio of 0.133
for Arctica collected in Rhode Island Sound (Arcisz and
Sandholzer 1947). Converted density of 0.051 kg/m 2 meat
weight derived for the entire survey area, and estimates of
0.087 kg/m 2 for Rhode Island Sound (Bearse 1976) and
0.011 kg/m 2 for the offshore waters of southern New
England (Murawski and Serchuk 1979b) were of the same
order of magnitude.

TABLE 1.

Total area, sample size, estimated density (total wet
weight [kg/m' ] ), and estimated biomass (total
weight and meat weight [mt]) for individual
depth intervals and for the entire survey area.

Depth Intervals (m)

18.3 - 27.4

27.5 - 36.5

36.6 - 45.7

Total

No. of
samples

26

101

85

212

Stratum

area
(km 2 )

6.0833 x 10 2

1.1197 x 10 3

9.3758 x 10 2

2.6656.x 10 3

Density
(kg/m 2 )

0.3746

0.3428

0.4176

0.3767

Variance

0.0199

0.0077

0.0082

Total
weight
(mt)

2.279 x 10 s

3.838 xlO 5

3.915 x 10 s

1.004 x 10 6

Meat

weight

(mt)

3.03 x 10 4

5.10 x 10 4

5.21 xlO 4

1.33 x 10 s

Minimum biomass for the entire survey area was esti-
mated at 1.004 x 10 6 mt total weight with a corresponding
estimate of 1.33 x 10 5 meat weight (Table 1). Murawski
and Serchuk (1979a) estimated the minimum biomass
(meat weight) of Arctica for the southern New England
region to be 1 .59 x 10 5 mt.

Effect of Substrate Type

Stepwise linear discriminant analysis was used to differ-
entiate between regions of high (> 0.75 kg/m 2 ) and low
(< 0.10 kg/m 2 ) ocean quahog density on the basis of sedi-
ment grain-size characteristics and water depth (Table 2).
Preliminary analyses indicated that the density of Arctica
was highest in medium-to-fme grain sand, and density
declined as mean particle size decreased (Figure 3). Estimated
density also was low in very coarse sand environments.
Ocean quahogs were not present in substrates comprised
primarily of gravel and stone, nor in those with high levels
of silt/clay.

TABLE 2.

Variables used in linear discriminant analysis differentiating

regions of high (> 0.75 kg/m 2 ) and low (<0.10 kg/m 2 )

ocean quahog densities.

Variable Code

Description

-10

00

+ 10

+ 20
+ 30
+ 40
+ 50
Shell
Depth
Mean
SC

% gravel (>2 mm)

%very coarse sand (1.0-1.99 mm)

% coarse sand (0.50-0.99 mm)

% medium sand (0.25-0.49 mm)

% fine sand (0.125-0.249 mm)

% very fine sand (0.062-0.1249 mm)

% silt/clay (<0.062 mm)

'", shell fragments

water depth (m)

mean grain size (0)

sorting coefficient (standard deviation)

10

0)6

Jt

- 4-1

Z J

2-

C- D

»-l

MEAN GRAIN SIZE (phi)

Figure 3. Ocean quahog density (kg/m 2 total weight) as a function
of mean grain size (0 units). Data given as mean (horizontal line)
± 2 standard errors (enclosed rectangle).

36

FOGARTY

Grain -size analyses were available for a total of 47 stations
assigned to the low-density classification and for 26 stations
designated as high-density sites. The stepwise discriminant
analysis was based on the pooled covariance matrix, and the
maximum F-ratio was used as the selection criterion.

Five variables were found to provide maximum group
separation (F 5(67 = 14.67. P < 0.01 ; Table 3). The relative
magnitude of the standardized discriminant coefficients
indicates the contribution of each variable to the discrim-
inating power of the function; the sign of the coefficients
denotes the direction of this contribution. The percentage
of three grain-size fractions (gravel, coarse sand, and silt/
clay) contributed negatively to the discriminant function
while the percentage of medium-grade sand and shell contri-
buted positively, confirming the results of preliminary
analyses (Figure 3). The remaining grain-size fractions did
not significantly enhance the discriminating power of the
function. Water depth did not significantly contribute to
the discriminant function, supporting inferences made
earlier; however, the depth ranges sampled were restricted.
The classification matrix indicating the actual and predicted
group membership based on the five discriminating variables
was:

Predicted

Actual

High Density

Low Density

High density
Low density

22 (84.6%)
4( 8.5%)

4(15.4%)
43(91.5%)

demonstrating the predictive power of the derived function
(89% correct classification).

TABLE 3.

Standardized stepwise discriminant coefficients for five

variables providing maximum separation of regions of

high (>0.75 kg/m 2 ) and low (<0.10 kg/m 2 )

ocean quahog density.

Variable

Coefficient

-l<t>

+ 10

+ 20
+ 50
Shell

-0.60647
-1.23598
+0.48943
-0.95893
+0.23318

DeWolf and Loosanoff (1945) described the preferred
substrate of Arctica as a mixture of sand and mud in Rhode
Island Sound. Parker and MacRae (1970) indicated that the
highest ocean quahog catches were made on sand and sandy
mud in exploratory surveys in the western North Atlantic.
Maurer et al. (1974) reported that Arctica was collected
most frequently on medium grade and coarse sand/shell
substrates in Delaware Bay.

Bearse (1976) utilized multivariate analyses to examine
the effect of sediment characteristics on the abundance of
Arctica at two locations in Rhode Island Sound. Stepwise
linear discriminant functions derived for one of these loca-
tions and for combined data, isolated different discrimin-
ating variables. Patchy distribution of sediments in the areas
studied was cited as a possible factor in conflicting results
between these analyses.

Bearse (1976) isolated organic carbon as one factor of
importance in determining ocean quahog distribution.
Phelps (1959) and Saila et al. (1967) demonstrated the
importance of organic carbon on hard clam (Mercenaria
mercenaria) distribution in Narragansett Bay. Although
carbon levels were not measured in the present study, it
was recognized that this variable may play an important
role in determining ocean quahog distribution patterns.

The observed relationship between ocean quahog density
and sediment characteristics cannot be taken to imply sub-
strate preference or selection. Particle-size distribution may
simply be the visible manifestation of other factors (e.g.,
current velocity, food availability), critical to ocean quahog
distribution (Bearse 1976). Further, dredge efficiency may
have varied with substrate composition and compaction,
resulting in biases in density estimates. These results retain
a practical significance, however, since the data may be
used to assess the probability of locating commercially
exploitable ocean quahog beds based on a knowledge of
substrate characteristics.

Size Composition

Shell length (standard length [SL] , longest linear dimen-
sion) measurements were obtained for a total of 1 1 ,925
ocean quahogs. Little variation in size frequency distribution
was noted between depth intervals (Figure 4), and no
significant differences (P < 0.05) in mean shell length were
detected when depth zones were compared using a one-way
analysis of variance.

Bearse (1976) reported a mean shell length of 90.5 mm
for samples collected by SCUBA and grab sample at two
sites off Rhode Island. Mean shell length noted in the
present survey was 88.5 mm; the similarity of these esti-
mates may indicate that the dredge provided relatively
unbiased estimates of size composition. DeWolf and
Loosanoff (1945) reported a mean shell length of 83.8 mm
for- samples collected by mechanical dredge in Rhode Island
Sound.

The maximum shell length noted in the present survey
was 1 14 mm. Murawski and Serchuk (1979a) reported that
ocean quahogs larger than 1 19 mm SL were seldom collected
off southern New England during survey cruises in offshore
waters, while samples collected off New Jersey frequently
contained individuals > 120 mm SL.

An attempt was made to separate the length-frequency
distribution into component size classes by the method of
Cassie (1954); however, it proved impossible to identify

Distribution and Abundance or Ocean Quahogs

37

probability modes with reasonable accuracy, a result con-
sistent with the slow growth rates demonstrated for this
species (Murawski et al., in press).

N = 1392

fl

^r^^

IP

60

80 90

SHELL LENGTH Imml

100

110

Figure 4. Shell length frequency distributions of ocean quahogs from
arbitrary depth intervals of 18.3-27.4 m (upper), 27.5-36.5 m
(middle), and 36.6-45.7 m (lower).

Regression equations relating meat weight and shell
length were derived for ocean quahogs assigned to three
arbitrary depth intervals and for combined data (Table 4).
Bearse (1976) derived a similar length-weight relationship
for Arctica in Rhode Island Sound:

W = 0.00091 14 L 2

(n= 129).

Murawski and Serchuk (1979c) reported the length-meat
weight relationship for ocean quahogs collected during

winter in the southern New England-Long Island region as

W = 0.0001090 L 2 - 775 (n = 1,351).

Direct comparisons between this equation and regression
equations developed in the present study were not possible
because of differences in the size range of sampled individ-
uals and in the time frame of sampling.

The higher meat yields predicted by the equations
derived in the present study and by Bearse (1976) may be
due to higher productivity in inshore waters, or by condi-
tion factors related to reproductive activity. Loosanoff
(1953) noted that the spawning period for Arctica extended
from June through October, with peak reproductive activity
in August and September off Rhode Island. More recent
work (Mann 1979) has indicated, however, that Arctica is
capable of spawning throughout the year and that spawning
activity may be intermittant.

Comparisons between parameter estimates for each depth
zone using Rao's homogeneity x 2 test (Rao 1973) indicated
no significant differences between depth strata for the
parameters a (xl = 0.378; ns) or b (\l = 1.261; ns).
Further comparisons for all possible pairwise combinations
for each parameter also indicated no significant differences
between depth zones. Parameter estimates for the shallow
depth strata exhibited relatively high variability (Table 4),
possibly due to the low sample size. Murawski and Serchuk
(1979c) did not detect any consistently significant differ-
ences in meat weight-shell length regression equations by
depth foi Arctica collected from the Middle Atlantic.

CONCLUSIONS

The estimated minimum biomass for the survey area,
1.36 x 10 5 mt meat weight, is high relative to recent
landings in Rhode Island (1,228 mt in 1979), indicating
that exploitation has not been severe. However, the slow
growth rate of this species (Murawski et al., in press) and
the presumably low natural mortality rate indicate that
productivity of the resource may be very low. The fishery
could conceivably be operating on accumulated biomass
without comparable recruitment. Although density esti-
mates derived from dredge data are necessarily minimum

TABLE 4.

Parameter estimates and asymptotically valid standard errors for allometric equation (W = aL ) relating
drained meat weight (g) and shell length (mm) for ocean quahogs off Rhode Island and Massachusetts.

Depth Interval

Parameter a

Asymptotic Standard Error

Parameter b

Asymptotic Standard Error

18.3 - 27.4

189

0.0013901

0.0012035

2.257166

0.183371

27.5 - 36.5

934

0.0006412

0.0002779

2.470849

0.095965

36.6 -45.7

710

0.0006282

0.0002656

2.482145

0.093499

Combined

1,833

0.0006585

0.0001732

2.463526

0.077496

38

FOGARTY

estimates, the results may be reliable indicators of total
harvestable biomass. These survey results are similar to esti-
mates derived using SCUBA and grab samples (Bearse 1976),
indicating that the hydraulic dredge may provide reasonable
density estimates. Medcof and Caddy (1971) reported an
efficiency of over 90% for a commercial hydraulic dredge;
there is considerable precedent for the use of dredge-type
sampling devices in assessment surveys of commercially
important marine bivalves (Saila et al. 1965; Russell 1972;
Loesch 1974; Loesch and Ropes 1977; Murawski and
Serchuk 1979a, 1979b).

Stratification of sample data into two classes, one of
which contained only zero catch values, allowed measure-
ment of the sample mean with relatively low variance.
Aitchison (1955) noted that estimates of the sample mean
derived in this manner can be best unbiased estimators,
i.e., have minimum attainable variance. This approach also
allows recognition of the fact that, in large scale surveys of
marine organisms, areas of unsuitable habitat will necessarily
contribute to a potentially high proportion of zero catches
(Pennington, personal communication), resulting in highly
skewed sample distributions.

Observations on the effect of sediment type on ocean
quahog distribution indicate that density is highest in sedi-
ments containing high proportions of medium (0.25—
0.49 mm) sand and shell fragments, and lowest in sediments
containing a high silt/clay fraction or coarse sand-gravel.
Stratification by sediment type may further increase the

precision of population estimates for this species in areas
where detailed substrate data are available.

Size-composition data for each depth interval generally
were similar; no significant differences in mean shell length
were detected. Estimated mean shell length for this survey
was similar to that determined by Bearse (1976), off Rhode
Island, based on in situ collections using SCUBA and grab
samples, possibly indicating that small individuals were
not a significant component of the population and that the
potential bias of the selection characteristics of the dredge
were minimized.

Shell length-meat weight regressions were similar to those
derived for Rhode Island (Bearse 1976), and indicated higher
meat yields than those predicted for the offshore waters of
southern New England (Murawski and Serchuk 1979c).

ACKNOWLEDGMENTS

This project was sponsored by the U.S. Department of
Commerce, NOAA, NMFS, Fisheries Development Division
(Grant 03-7-043-35 1 19). I am gTateful to R. Sisson,T. Lynch,
A. Ganz, and R.Wood for assistance at sea, and to S. Desillier,
P. Kullberg, C. Coyne, and K. Billington for laboratory
analyses. I thank B. Simon for programming and data man-
agement. S. Murawski and F. Serchuk reviewed the manu-
script and offered many helpful suggestions. I am grateful to
S. Saila for Ins encouragement and review of an earlier draft
of this manuscript. D. Dearse generously provided advice and
shared his expertise on ocean quahog distribution patterns.

REFERENCES CITED

Aitchison. J. 1955 On the distribution of a positive random variable
having a discrete probability mass at the origin. J. Am. Stat.
Assoc. 50:901-908.

& J. A. C. Brown. 1957. The Lognormal Distribution.

Cambridge Univ. Press. 176 pp.

Arcisz, W. & W. C. Neville. 1945. Description of the fishery. Pages
7-14 in The Ocean Quahog Fishery of Rhode Island. Rhode
Island Department of Agriculture and Conservation, Division of
Fish and Game.

Arcisz, W. & L. A. Sandholzer. 1947. A technological study of the
ocean quahog fishery. Commer. Fish. Rev. 9:1 -21 .

Bearse. D. T. 1976. Density and distribution of the ocean quahog
(Arctica islandica) in Rhode Island waters relative to various
environmental factors. M.S. thesis. University of Rhode Island,
Kingston. 91 pp.

Cassie, R. M. 1954. Some uses of probability paper in the analysis
of size frequency distributions. Aust. J. Mar. Freshw. Res.
5:513-522.

& A. D. Michael. 1968. Fauna and sediments of an inter-
tidal mud Hat: a multivariate analysis. J. Exp. Mar. Biol. Ecol.
2:1-23.

DeWolf. R. A. & V. L. Loosanoff. 1945. Biology of the ocean
quahog. Pages 14-15 in The Ocean Quahog Fishery of Rhode
Island. Rhode Island Department of Agriculture and Conserva-
tion, Division of Fish and Game.

Fisher, R. A. 1936. The use of multiple measurements in taxonomic
problems. Ann. Eugen. [Annals of Human Genetics] 7:179 -188.

Fogarty, M. J. 1979. Assessment of the ocean quahog, Arctica
islandica. resource in Rhode Island Sound and south of Martha's

Vineyard, MA. Final report. Rhode Island Dept. Environ. Man.,
Div. Fish Wildl. Contract 03-7-043-35119.44 pp.

Krumbein, W. C. & F. J. Pettijohn. 1938. Manual of Sedimentary
Petrology. Appleton-Century-Crofts, Inc., New York. 549 pp.

Loesch, J. G. 1974. A sequential sampling plan for hard clams in
lower Chesapeake Bay. Chesapeake Sci. 15(3): 134- 139.

& J. W. Ropes. 1977. Assessment of surf clam stocks in

nearshore waters along the Delmarva Peninsula and in the fishery
south of Cape Henry. Proc. Nat. Shellfish. Assoc. 67:29- 34.

Loosanoff, V. L. 1953. Reproductive cycle in Cyprina islandica.
Biol. Bull. (Woods Hole) 104:146-155.

Mann, R. 1979. The biology of the ocean quahog. Arctica islandica.
Sea Grant Project Summary. Woods Hole Oceanographic Institu-
tion, Woods Hole, MA 02543. 29 pp.

Maurer. D.. L. Watling & G. Aprill. 1974. The distribution and
ecology of common marine and estuarine pelecypods in the
Delaware Bay area. Nautilus 88:38-45.

Medcof, J. C. & J. F. Caddy. 1971. Underwater observations on
performance of clam dredges of three types. Int. Counc. Explor.
Sea CM. 1971/B:10.

Merrill, A. S. & .1. W. Ropes. 1969. The general distribution of the
surf clam and ocean quahog. Proc. Nat. Shellfish. Assoc. 59:
40-45.

. 1970. The distribution and density of the ocean quahog,
Arctica islandica. Am. Malacol. Union Inc. Bull. 36:19.

Murawski, S. A. & F. M. Serchuk. 1979a. Dynamics of ocean
quahog, Arctica islandica. populations off the Middle Atlantic-
coast of the United States. National Marine Fisheries Service.
Woods Hole Laboratory Ref. 79-16 (mimeo).

Distribution and Abundance of Ocean Quahogs

39

. 1979b. Distribution, size composition, and relative

abundance of ocean quahog, Arctica islandica, populations off
the Middle Atlantic coast of the United States. Int. Counc.
Explor. Sea CM. 1979/K:26.

. 1979c. Shell length-drained meat weight relationships of

ocean quahogs, Arctica islandica. from the Middle Atlantic shelf.

Proc. Nat. Shellfish. Assoc. 69:40-46.
Murawski, S. A., J. W. Ropes & F. M. Serchuk. 1981. Growth of the

ocean quahog, Arctica islandica. in the Middle Atlantic Bight.

Fish. Bull.. U.S. (in press).
Parker, P. S. & E. D. McRae. 1970. The ocean quahog, Arctica

islandica. resource of the northwestern Atlantic. Fish Ind. Res.

6:185- 195.
Phelps, D. K. 1959. A study of the relationship between certain

marine invertebrates and the physical and chemical environment

of Narragansett Bay. Pages 1 - 1 4 in Hurricane Damage Control-

Narragansett Bay and Vicinity, Rhode Island and Massachusetts.

a Detailed Report on Fishery Resources. Appendix G. U.S. Fish

and Wildlife Service.
Ralston, M. L. & R. I. Jennrich. 1978. Dud, a derivative-free algorithm

for nonlinear least squares. Technometrics 20:7-14.

Rao, C. 1973. Linear Statistical Inference and Its Applications.
John Wiley and Sons, Inc., New York. 625 pp.

Ropes, .1. W. 1979. Biology and distribution of surf clams (Spisula
solidissima) and ocean quahogs (Arctica islandica) off the
northeast coast of the United States. Pages 47-66 in Proc.
Northeast Clam Industries: Management for the Future.

Russell, H. J. 1972. Use of a commercial dredge to estimate a hard-
shell clam population by stratified random sampling. J Fish.
Res. Board Canada 29:1731-1735.

Saila, S. B., J. M. Flowers & R. Campbell. 1965. Applications of
sequential sampling to marine resource surveys. Ocean Sci. Eng.
2:782-802.

Saila, S. B., J. M. Flowers & M. T. Cannario. 1967. Factors affecting
the relative abundance ofMercenaria mercenaria in the Providence
River, Rhode Island. Proc. Nat. Shellfish. Assoc. 57:83-89.

Serchuk, F. M., S. A. Murawski. E. M. Henderson & B. E. Brown.
1979. The population dynamics basis for management of off-
shore surf clam populations in the Middle Atlantic. Pages 83- 101
in Proc. Northeast Clam Industries: Management for the Future.

Journal of Shellfish Research, Vol. 1, No. 1,41-49, 1981.

RESPONSE OF SOFT-SHELL CLAM (MYA ARENARIA ) GROWTH TO
ONSET AND ABATEMENT OF POLLUTION

RICHARD S. APPELDOORN

Graduate School of Oceanography
University of Rhode Island
Kingston, RI 02881

ABSTRACT Length-frequency analysis was used to generate age-length curves for six populations of the soft-shell clam
Mya arenaria exposed to a sudden pollution event. Five populations were each subjected to a single oil spill. A sixth popula-
tion was subjected to the onset and subsequent abatement of the effluent from a heavy metals mine. With one exception,
the onset of pollution was accompanied by a noticeable break in the age-length curve representing a decrease in growth rate
following the event. At the site where abatement occurred, the age-length curve showed a second break indicating resump-
tion of near-normal growth. An attempt is made to relate severity and persistence of the pollution effect on growth to the
degree of deflection in the age-length curve. A method that estimates prepollution growth is presented and applied to two
populations.

INTRODUCTION

The need for more information on the effects of pollution
in marine ecosystems has long been recognized. However,
only recently has significant progress been made. Early
investigators studied only acute lethal effects, and variability
in the number and reliability of the methods involved led
to much confusion (Hyland and Schneider 1976). With
improving methodology there has been increased interest
in chronic and sublethal effects (Anderson 1977). Coupled
with this has been the realization that such research should
concern itself with population processes rather than with
individuals (Vanderhorst et al. 1978). Notable studies
involving long-term monitoring of populations following a
pollution event are those of the West Falmouth oil spill
(Sanders et al. 1980), the Chedabucto Bay oil spill (Thomas
1978), and studies of pulp mill effects in Sweden (Rosenberg
1976). One major problem in studying the effects of a
sudden environmental change is the availability of reliable
control data from either measurements made prior to the
change or from a suitable control area.

Recently, the status of soft -shell clam {Mya arenaria)
populations and their relationship to various forms of pollu-
tion have been investigated (Brown et al. 1979). In this
investigation samples were collected from several sites
characterized by a sudden change in environmental quality
due to onset or abatement of pollution. Growth was one
of the parameters studied; the effect of each pollution
event on growth obviously was of particular interest.

The primary purpose of this paper is to present age-
length curves of soft-shell clam populations from sample
sites where a pollution event occurred. Based on a few
assumptions, these curves can be used to represent growth.
This paper also shows that a sudden change in environ-
mental quality resulting from the onset or abatement of
pollution is reflected by a shift in the age-length curve. In
addition, a method is presented whereby growth prior to a
pollution event may be estimated.

METHODS

Clam growth was studied at six sites where a discrete
pollution incident (either onset or abatement) occurred.
Five of the sites were affected by spills of various types of
oil. The sixth site was exposed to the effluent from an inter-
tidal heavy metals mine. Table 1 lists the sampling sites,
briefly characterizes each area, and provides estimates for
the extent of polltuion.

Each site was sampled once with the exception of Sears-
port which was sampled quarterly in 1977 and 1978. Clams
were dug with a standard clam hoe. All excavated clams
were measured for length to the nearest millimeter using
vernier calipers. For Searsport, length data for clams setting
after the spill were obtained from Dow (1978, Table 2,
p. 47), who used growth-ring measurements on live clams
from the 1971 year-class.

Clams were aged using length-frequency analysis to obtain
growth rates. The single exception was Goose Cove where
shell-ring counts were used exclusively to age the clams.
Length-frequency analysis was based on the assumption
that modes in the length-frequency distribution represented
different cohorts and that size was distributed normally
within a cohort (Cassie 1954, Tanaka 1962, Tesch 1971).
This assumption of normality was seldom exact because of
stacking effects as growth decreased in larger individuals
(van Sickle 1977), and because of size-dependent mortality,
generally affecting the smaller members of each cohort. The
degree of skewness introduced by these processes was
assumed to be small. Because the interest was on relative
shifts in the age-length curve rather than on the exact
description of that curve, the consequences of skewness
were rendered negligible.

Length-frequencies for each population were plotted at
1-mm intervals; modes on the resulting graph were broken
down into a series of normal curves by the Peterson method
using a Dupont 310 curve resolver, an analog computer
which allowed the investigator to break down a complex

41

42

APPELDOORN

&

<

o

o

Oh

o

S °

o ;=,

~ o
a. .5

S 3

5 =

x o c

3
33 °

>,' 5

<u E

« -a —

S •-

C3
3 2?

o S

E o

.5 3 " c

(Si a>

i—
0)

S3

in

>

S.

^

c

——

6

CT>

o

'3

—

i—

3

"a>

=3

.3

ri

-O

fC

s

—

r-i

CD

_:

o

D,

a>

z

21

S.

_3

HE

<

3

s

'_f

a>

X

c

S

-a

5

C3

u

o

ca

X

x

£ 7

o 3=
,_, w .— i.

— ' •£? o>

cd

^ c

a. -

1 -

ra '■*- t; — o

5

u

C

ON

T3

cd

(/)

Cd

<

o

c

CO

+2

"cd

£

-

<u

-

CJ

_>

a>

X

cd

3

o

61

-*■ p-,r, li -*- 1

c « !2 c

2 "o ~ 42

S - ag

C ^3 3 —

a> o

c j « c

" ^. 3 "5.

« o o p

r- ' — _

--* _

S v

•a .tl

^ OO

3. o. 22

ra T3

3 -O
l> 3

;S Z -o c/)

<

s

_ o
c 5

■e «

££

d ri 6t

= x

.2 oo

o o
E ~

" 5 o
C " o ro

H O

o 5
o 2

cj 3

_C o

~ o

- t-. u

2 -c 42
>, 2 j?

3 °-

III
II J

•— c -a

«. ^ a

5 £ -a

^ rt
"S. S 3

E "2 «
2 o "

■~ c 5

io rt o

. -a .S

« » -g

u K S
o SS

s-S S

C 3
O T3

■o S c
n 2 o

5 4= C

s -

2 E

c

—

c

CO

o

X

(J

y

o = ■
"53 5. ,

o « «
Z .3i,S

_

S

<D

>

o
U

s

oo

trt

C

'- 1 :

o

a>

-1

1/3

3 C

u S

T3

■a

_r:

3

O

E

C

T3

o

c

O

cd

T3 ^ 4>

a t J
■a j2 >

Ui

22 S o

a » »

O on ^-^

4= s »

3 >. ^

s «> -

. c c

— i <u r:

° rt 3

o I E

° E 42
o 22 |

r<> 3 >
CA

-I 9

"" M 5

t-* 4» «
CU N 2

§|1
°-§3

■3 u 2

< 3

5 bO

X E

O o

60 •£

o •&

3 3

"SB >,
3.x.

o -a

.5 >. -a
-S =3 c

■° c 2 —

blj ^t

"OS;

•a c oj

ITS 3

Ill

o

o ™ S u

42 00

O o r-

m '5 ^

J a. C

-

V

5

■_J

o>

M

<

'-'

c

cy

X

3

t-1

£Q

~

-1
3

— '

E

E.

CD

c t3 a

O

O Cd

_

—1 -

s

3 C

O 0-

E E

16

E O

u

in
in

~z

>

PL,

E

T3

(L>

in

4T

3

O
CD

2

CD

'A

SI

B
O

c

Tf

>

T3

CO

Z

_0

3

C

-,

C
r*

in

u

!>>

— c .3

2 u

C-^ CL "^3 -3

E o

Q O

^ > 3

n K5

O -a

— .„ ON

3 n -1

_

S

CJ

>

a>

3

'c/5

a?

O

-C

O X

0.

E

cd

00

^;

>,

j;

O,

cd

a

^

•S c

&

■«

E M

.2

a a

" 1

cd c
00 3

"

>»

X) _

->_, cd

JZ S

DO O

'S 5C

> CU

>. _5

■5 ai

60 _T

■~~~ 3

00 O

3 1

— c

0J w

■■5 1

cu cd

0"\

.^ —

C/5

■si

™

a> O

^_-

|2

B

_3

1—

c °

—

•2 &

b

rt 52

-!=: at

V)

c 2

p^

c 3

■^

cd

-

*a

3 S
cd

u

O

a,
cu

a

•13 cu

cd

^ £i

.5

■= 3

5b

— O

<^

Response oi Soi t-Shell Clam Growth to Pollution

43

envelope into its basic components (in this case normal
curves) in a graphical fashion. It utilized 10-function gen-
erator channels each capable of generating a normal curve
on a cathode-ray tube. The images of those curves could
then be projected onto a length-frequency histogram. The
histogram was broken down from left-to-right (young-to-
old) in the following manner.

One channel was switched on and the projected curve
was positioned such that its location, width, and height
corresponded to the left edge of the histogram. The
remainder of the histogram was then resolved by successively
turning on the channels and positioning them such that the
envelope projected (formed by the summation of the out-
puts of all the "on" channels) matched the outline of the
histogram. The optical output gave the observer immediate
feedback, and repeated trials could be made quickly by
varying size, shape, position, and number of curves until a
reasonable "fit" to the data had been obtained. At that
point, the output of each channel could be turned on and
displayed independently, and its projection traced on the
histogram. The result of this process is exemplified in
Figure 1 .

From the resulting graphs, mean and standard deviations
of each distribution were obtained (Macdonald and Pitcher
1979). The mean occurred at the peak; the standard devia-
tion was the half width at 61% of the height (Figure 1,
curve 4). The curve resolver was equipped with an integrator
enabling the investigator to obtain the percentage of the
whole sample under each component curve.

Ages were assigned to each cohort (Brothers 1979) by
inspecting the histograms and subsequent age-length curves,
and taking into consideration local recruitment processes
and sampling efficiency. These results were corroborated by
comparing them to previously published age-length data
for the same or nearby areas (e.g., Belding 1930, Dow 1978,
Appeldoorn 1980). Additional corroboration was sought
for the Searsport sample by using annual shell-ring counts
on a subsample of clams to develop a rough age-length key.

The ages assigned were relative rather than absolute where
the time beyond the least yearly increment represented the
percent of expected yearly growth already obtained. Hypo-
thetically, if a clam first set in the beginning of April and
was collected in November, 3 years later, its relative age
would be 4 rather than 3.6 because it no longer would be

40
x +1 SD

LENGTH (mm)

Figure 1. Length-frequency histogram for Janvrin Lagoon with superimposed distributions for each age group as determined with the curve
resolver. Solid curves represent age groups. Dashed curves represent the total fitted envelope. The mean plus one standard deviation (SD)
are shown for the fourth curve. Numbers above the curve represent the percentage of the sample under each curve, respectively.

44

APPELDOORN

expected to grow significantly during the rest of its third
year. The size obtained by November would equal roughly
its size at age 4. This process resulted in a smoother growth
curve since it avoided the problems of seasonal variations
in the growth rate which would otherwise necessitate the
use of a more complex growth model (Cloern and Nichols
1978).

For three sites. West Falmouth, Searsport, and Janvrin
Lagoon, sufficient numbers of year classes were represented
to allow a von Bertalanffy growth curve to be fitted to the
data (von Bertalanffy 1938). Only postspill age classes were
used to fit the curve which reduced the number of points
available for analysis. The growth curve was fitted by non-
linear regression according to Gallucci and Quinn (1979)
using the NLIN procedure of SAS 76 (Barr et al. 1976).
This procedure yielded estimates of the parameters for the
von Bertalanffy growth equation:

L = L^ < 1 - exp [— K (t - t

oM }

where t = time, L = length at time t, L^ = maximum
asymptotic length, K = growth constant, and t = time
when L = 0.

Using the calculated von Bertalanffy curve, the growth
rate prior to pollution was estimated. This analysis was
based on the assumption that growth followed a fixed
schedule or pattern. Growth prior to pollution may be
different (i.e., have its own growth schedule) from growth
after pollution. It was assumed that the postpoUution growth
schedule was adequately modeled by the calculated von
Bertalanffy curve. The prepollution growth schedule was
then approximated in the following manner.

The length (L,) was found of the last year-class to set
prior to pollution. Then the age was determined corres-
ponding to that length on the von Bertalanffy curve. One
year was subtracted from that age and its corresponding
length (L 2 ) was determined on the growth curve. Next the
length (L 3 ) was found corresponding to an age equal to age
at Li — 1 . The difference between L 2 and L 3 represented
the extra growth experienced by clams having one year of
growth on the prepollution growth schedule. That difference
was then added to the expected length at year one on the
postpoUution curve (von Bertalanffy curve) to obtain the
expected length at year one on the prepollution curve. The
second point on the prepollution schedule was found by
applying the above procedure to the year class that had set
2 years prior to pollution. That process was repeated for all
available prepollution year classes.

RESULTS

Mean length and standard deviation are shown in Table 2
for each age group per site as obtained from the length-
frequency analysis. These data are plotted in Figures 2
through 7. The calculated von Bertalanffy curves for West
Falmouth, Searsport, and Janvrin Lagoon, are also plotted;

parameters for those curves are given in Table 3. Prepollution
growth approximations for Searsport and Janvrin Lagoon
also are plotted. For the remaining three areas, approximate
curves have been drawn "by eye" to smooth out the age-
length relationship and to accentuate its change following a
pollution event.

These figures demonstrate that changes in the incidence
of pollution were reflected by changes in the growth rate.
Only West Falmouth failed to show a significant change.
Breaks in the curves clearly indicate that pollution has had
an adverse effect on growth, and they also reflect the
degree to which growth had been reduced. Growth was
severely affected at Searsport, Janvrin Lagoon, and at
Goose Cove. At Goose Cove growth improved following
pollution abatement. At West Falmouth the lengths of the
year classes existing prior to the spill failed to differ signifi-
cantly from the lengths expected on the basis of postspill
growth. It appears that the spill had no drastic effect on
growth of clams from the collection site.

For comparison purposes, the age-length determinations
for Potato Island (Appeldoom 1980) are plotted in Figure 2.
That area was used as a control site by Thomas (1978), and
by Gilfillan and Vandermeulen (1978) in their studies of
Chedabucto Bay. In the latter study, it was reported that
soft-shell clam growth at Janvrin Lagoon and Potato Island
were similar prior to the spill. The estimate of prespill
growth calculated in this study agrees remarkably well with
the age-length determinations for Potato Island.

The parameters of the von Bertalanffy curve for Searsport
appear anomolous in comparison to the other values shown
in Table 4. That probably resulted from sampling errors
(note the standard deviations in Table 3) associated with a
small sample size (N = 15), and from successive improve-
ments in postspill growing conditions. The latter would
tend to increase the initial slope of the age-length curve,
thereby increasing K.

DISCUSSION

The problems inherently associated with the estimation
of population age structure and growth through length-
frequency analysis were reviewed by Brothers (1979),
Macdonald and Pitcher 1979), and others. A reiteration of
those problems is not necessary here. It should be pointed
out, however, that the growth measured herein is for a
cohort of the population and not for individuals (see Ricker
1975, pp. 217-218). The difference between the two arises
because the older modes in the length-frequency histogram
usually are composed of slower growing individuals. Gerking
(1957) has shown for fish that rapidly growing individuals
tend to mature, become senile, and die, earlier than slower
growing individuals. In general, for Mya arcnaria, an inverse
relationship has been found between longevity and the rate
of growth (Newcombe 1936), i.e., older clams are slow
growers. A good example has been shown by Dow (1978)
for clams growing at Searsport. As clams grow their burrow

Response oi Soft-Shell Clam Growth to Pollution

45

TABLE 2.

Mean length and standard deviation as determined by length-
frequency analysis for sample population at six sites.

Age

(yr)

Length
(mm)

Standard Deviation

Basset's Island, Bourne, MA (N = 187)

Sample

(%)

1.15

22.7

2.2

8

2.15

3CX6

2.4

5

3.15

40.8

2.4

14

4.15

48.2

2.3

27

5.15

54.4

1.3

10

6.15

58.9

1.5

9

7.15

64.3

2.1

12

8.15

70.5

1.3

8

9.15

75.7

2.0

3

West Falmouth, MA (N = 183)

1.15

28.6

2.6

9

2.15

38.8

2.6

3

3.15

45.2

1.5

2

4.15

53.3

2.9

27

5.15

61.6

1.5

8

6.15

68.2

1.9

20

7.15

73.4

1.7

7

8.15

78.8

1.4

5

9.15

84.5

2.6

1

Goose Cove, Ha

borside, ME (N

= 101)'

3

24.1

1.9

7

4

34.3

3.8

12

5

36.4

4.1

25

6

39.6

3.2

23

7

46.6

9.8

5

8

47.7

17.2

17

9

55.2

6.9

6

10

61.5

2.1

2

11

59.5

5.8

4

Janvrin Lagoon, Nova Scotia, Canada (N = 201)

3.5

21.0

0.5

4.5

26.7

0.7

3

5.5

29.9

0.9

6

6.5

32.6

0.8

11

7.5

36.2

1.3

24

8.5

39.7

1.0

24

9.5

43.8

1.0

17

10.5

47.4

1.0

11

11.5

50.3

1.0

3

12.5

54.0

0.5

Long Cove, Searsport, ME (N =

152) 2

1

10.0

3.0

2

18.3

3.7

3

24.9

3.7

4

31.1

4.2

5

34.4

4.5

6.2

38.0

0.6

2

7.2

41.5

1.4

3

8.2

44.9

1.0

6

9.2

47.2

0.6

5

10.2

49.9

1.0

14

11.2

53.0

1.2

15

12.2

55.3

0.7

11

13.2

57.0

0.8

10

14.2

59.0

0.9

18

Gleason Cove

Perry, ME (N =

180)

3.67

36.4

1.5

3

4.67

41.1

1.5

11

5.67

47.1

1.8

29

6.67

55.2

2.3

46

7.67

62.3

0.8

5

8.67

66.9

0.8

3

9.67

70.9

1.9

100

80

E 60

E

o

20

JANVRIN LAGOON

SPILL

4 6 8 10
AGE (y eors)

12

Figure 2. Age-length curve for Janvrin Lagoon, Nova Scotia,
Canada. Open ciicles: mean length at age for each age-class.
Closed circles: calculated estimates for mean length at age
prior to spill. Triangles: mean length at age for Potato
Island, a control site. Lower line: postspill growth pre-
dicted by the von Bertalanffy equation. Upper line: prespill
growth and was drawn by eye.

100 r

Ages determined by counting shell rings.
First five year-classes from Dow (1978).

4 6 8 10

AGE ( years )

Figure 3. Age-length curve for Long Cove, Searsport, ME.
(All symbols as in Figure 2.)

46

APPILDOORN

100

80

E60

E

2 40

UJ

20

PERRY

SPILL

j_

_L

4 6 8 10
AGE (years)

4 6 8 10

AGE ( yea rs )

Figure 4. Age-length curve for West Falmouth, MA. (AU symbols as Figure 6. Age-length curve for Gleason Cove, Perry, ME. Circles: as
in Figure 2.) in Figure 2. Solid line: age-length relationship (drawn by eye).

100

80

£ 60

E

Z 40

20

BOURNE

SPILL

_L

100

80

E 60

E

z 40

20

j_

_L

GOOSE COVE

MINING
STOPS

MINING
STARTS

_L

4 6 8 10

AGE (years)

12

4 6 8 10

AGE (years)

12

Figure 5. Age-length curve for Basset's Island, Bourne, MA. Circles:
as in Figure 2. Solid line: age-length relationship (drawn by eye).

Figure 7. Age-length curve for Goose Cove, ME. Circles: as in Figure 2.
Solid line: age-length relationship (drawn by eye).

Response 01- Soi t-Shell Clam Growth to Pollution

47

TABLE 4.

Parameters for von Bertalanffy growth equation fitted to
postspill age classes of soft-shell clams from three areas.

Area

K

Loo

t
o

West Falmouth, MA

Janvrin Lagoon, Nova Scotia. Can.

Scarsport, ME

0.0917
0.05 75
0.2358

136.73
88.74
50.48

-1.357

-1.622

0.074

depth increases. Faster growing clams were penetrating the
buried stratum of oil-polluted sediment at an earlier age
whereup mortality occurred. Hence, only the slower growing
individuals survived; they now constitute the bulk of the
older age groups in the population.

The assumption that clams grow according to a fixed
schedule (especially after a pollution incident) probably is
not valid. For example. Dow (1978) has shown successive
improvements in growth of M. arenaria for each year-class
following the Searsport oil spill. This was due to both the
further weathering of the oil, and the further deposition of
clean sediment over the oil-contaminated sediment. However,
at Searsport and at Janvrin Lagoon postspill recovery has
been slow enough to allow the use of the von Bertalanffy
curve to generate prespill growth estimates. Since only
approximate growth estimates have been obtained, no
effort was made to apply rigorous statistical analysis to
the data.

The results show that there was a response in the growth
rate to environmental changes caused by pollution. That
response was characterized by a noticeable break in the age-
length curve. In each case the onset of pollution was coupled
with a reduction in growth. The exact mechanisms for the
observed growth reductions at each site are unknown. The
volume of literature on the effects of pollution on marine
organisms in general, and on bivalves in particular, is vast
but it is still difficult to relate specific effects in the labora-
tory to responses observed in the field.

Other field studies of M. arenaria have shown that the
onset of oil pollution generally was followed by a reduction
in growth and an increase in mortality. Dow (1975) found a
65% reduction in annual growth rate of clams transplanted
to a site polluted with Iranian crude oil. At Searsport,
Dow (1978) reported a reduction in growth of soft -shell
clams following the spill. Mortality at Searsport greatly
increased when clams burrowed into oiled sediment indi-
cating either a direct toxic effect or smothering (Dow and
Hurst 1975, Dow 1978). Smothering was considered the
main cause of the large soft-shell clam mortality following
the spill of Bunker C oil at Chedabucto Bay (Thomas 1973).
Gilfillan and Vandermeulen (1978) found a reduced carbon
flux in soft-shell clams from Janvrin Lagoon as compared to
Potato Island. This was coupled with a calculated reduction
in the rate of shell growth in Janvrin Lagoon clams following
the spill. In an earlier study, Gilfillan et al. (1976) found a

50% reduction in the carbon flux of soft-shell clams polluted
by No. 6 fuel oil. They concluded that for bivalves a reduc-
tion in the assimilation ratio was a general response to
environmental stress which could be triggered by a number
of factors including pollution.

The age-length curve for West Falmouth failed to show a
break at the time of the spill. There are two possible explana-
tions for this. First, because sampling took place 8 years
after the spill, it could be possible that the sample age
masked any true effect. Only 6% of the sample consisted of
clams that had set prior to the spill. Such a small sample
size could have led to underestimation of the mean lengths
for each age class.

Second, the curve could accurately reflect the true
effect of the spill on growth. While this may be true, studies
made after the spill indicated initially severe effects. Blumer
et al. (1970) reported numerous mortalities among the
benthos, including shellfish, immediately following the spill.
Site II particularly was devastated (Sanders 1978); high
concentrations of hydrocarbons were found in shellfish from
the tidal creek (Blumer et al. 1970) one month after the
spill. It seems unlikely, then, that clam growth would have
remained unaffected. With improving conditions, however,
any effect might become unnoticeable. Sediment oil concen-
trations at Site II decreased steadily over time reaching
140 jug/g after 2 years, only twice the level reported for
indigenous sedimentary hydrocarbons within the area
(Blumer and Sass 1972). The degree of this decrease may be
attributable to sediment characteristics at the sampling site.
Loose, coarse, shifting sand should facilitate rapid depura-
tion or burial of the oil; therefore, growth may have been
affected only during the first few years. Significantly
improving conditions invalidate the assumption of a fixed
postspill growth schedule. Hence, the von Bertalanffy curve
cannot be expected to approximate the growth of an
affected population. With the sampling problems mentioned
above, and the 8-year time lag between sampling and the
spill, any initial effect on growth now would be undetect-
able by the methods used. The West Falmouth situation
differed from both the Bourne and the Perry sites, where
little oil was found when sampled shortly after the spill,
and the Searsport and Janvrin Lagoon sites, which were
sampled several years after contamination but still con-
tained enough oil to affect growth adversely.

Mining operations at Goose Cove could have led to a
reduction in growth via three mechanisms: siltation. food
destruction, and direct heavy metal toxicity. Dow and Hurst
(1972) suggested that much of the damage caused by the
mining operations resulted from heavy siltation and
smothering. These would definitely interfere with feeding
by clogging the gills of the clams. They also reported that
the mine effluent was highly toxic to phytoplankton, the
main food source for soft-shell clams, and that alone could
contribute to malnutrition and starvation. Eisler (1977)
reported that M. arenaria was susceptable to heavy metal

48

APPELDOORN

contamination. Many of the metal concentrations reported
by Dow and Hurst (1972) were higher than the lethally toxic
concentrations found in bioassay studies dealing with pure
(Eisler and Hennekey 1977) and mixed (Eisler 1977) metal
solutions. Conditions in the field and laboratory differed
significantly, thus, the observations were not directly com-
parable, but it was evident that the levels found at Goose
Cove were relatively high.

Concentrations of metals in soft-shell clams at Goose
Cove were still high at the time of sampling, 4 years after
mining operations had ceased (L. Fink, University of Maine,
Walpole, personal communication). It can be seen from the
graph in Figure 7 that growth improved following pollution
abatement, although it did not return to its original rate. If
starvation and smothering were major factors contributing
to reduced growth, then growth should have improved
dramatically upon cessation of mining activities. This could
have been the case; however, the exact degree of recovery
was difficult to assess because of variability of the data.
These observations showed that smothering and starvation
were major factors working in conjunction with direct
toxicity to reduce growth during the period of mining
operations. In addition, to some extent, it appeared that
growth was still being affected adversely at the time of
sampling perhaps because of direct toxic effects.

The pronounced growth reduction at Goose Cove can be
attributed to (1) the variety of ways in which the mining
effluent affected the clams, and (2) the constant output of
effluent during mining operations. Once mining operations
ceased, recovery was fairly rapid. This was in contrast to
growth recovery at oil-polluted sites, and reflected the
persistence of oil remaining in the sediment, and the
different mechanisms by which oil and mining effluents
affect clams. Major contributing factors to reduced growth
at Goose Cove, such as siltation and food reduction, were
removed after mining operations ceased. On the other hand,
oil itself is a major factor in growth reduction. Oil can be
taken in through the siphons (Fong 1976), and oil leaching
from saturated sediments following a spill can result in a
contaminated water supply for an extended period of time
(Mayo et al. 1975). Because oil can be detrimental upon
contact (Dow 1978), the effects of a spill can persist after
burial of the oiled sediment. In addition, Vandermeulen
(1977), and Vandermeulen and Penrose (1978) found that

significant quantities (40%) of oil remained in polluted
soft-shell clams following a 3-month exposure to clean
water. All of those factors contributed to the persistance of
a growth reduction effect following initial hydrocarbon
contamination.

Some areas sampled, though, did show signs of recovery.
No break in the age-length curve was observed at West
Falmouth as discussed earlier. Bourne seems to be a similar
case. Little evidence of oil was found at the time of sampling,
and the break in the curve (Figure 5) appears like a short
depression in an otherwise normal growth curve. This would
indicate that growth was disrupted only for a short period
of time, on the order of a few years.

The techniques used here are considered valuable in
assessing pollution effects. Primarily they are useful in
detecting gross responses in growth due to changes in environ-
mental quality and they allow estimation of prepollution
growth. This is helpful because measurements taken prior
to a pollution event are rare and usually fortuitous. A
number of studies have used shell-growth bands to monitor,
in detail, subtle environmental changes (e.g., Kennish and
Olsson 1975). However, these techniques are limited in
their application and the methods are involved and costly.
The techniques used here sacrifice detail but have more
general applicability. For example, by using these techniques,
studies are possible of M arenaria populations south of Cape
Cod where annual ring formation is unreliable (Mead and
Barnes 1904, Shuster 1951). The responses observed only
directly reflect the effects on growth. They do not directly
reflect changes in mortality, settlement, or population age
structure. As was observed at Searsport, however, continued
size-dependent mortality may indirectly affect the resulting
growth curve.

ACKNOWLEDGMENTS

The author expresses gratitude to those persons and
agencies who assisted in clam collection, in particular,
R. L. Dow and M. Richards, Maine Department of Marine
Resources; J. M. Hickey, Massachusetts Division of Marine
Fisheries;andM. L.H.Thomas, University of New Brunswick.
Collection was funded by a grant from the American
Petroleum Institute. Saul Saila reviewed the manuscript and
provided helpful criticism.

REFERENCES CITED

Anderson, J. W. 1977. Responses to sublethal levels of petroleum
hydrocarbons: are they sensitive indicators and do they correlate
with tissue contamination? Pages 95-114 in D. A. Wolfe (ed.),
Fate and Effects of Petroleum Hydrocarbons in Marine Ecosys-
tems and Organisms. Pergamon Press. New York. 478 pp.

Appeldoorn, R. S. 1980. The growth and life-history strategy of the
soft-shell clam , Mya arenaria L. Ph.D. thesis. University of Rhode
Island, Kingston, Rl. 115 pp.

Harr, A. 1., J. H. Goodnight, J. P. Sail & J.T. Helwig. 1976. A User's

Guide to SAS 76. Sparks Press, Raleigh. North Carolina. 329 pp.
Belding, D. L. 1930. The soft shelled clam fishery of Massachusetts.

Mar. Fish. Sen'., Div. Fish Game Mass. 1:1-65.
Bertalanffy, L. von. 1938. A quantitative theory on organic growth

(inquiries on growth laws. II.). Human Biol. 10: 181 -213.
Blumer, M. & J. Sass. 1972. Oil pollution: persistence of degradation

of spilled fuel oil. Science 1 76 : 1 1 20- 1 1 22.
Blumer, M., G. Souze & 1. Sass. 1970. Hydrocarbon pollution of

edible shellfish by an oil spill. Mar. Biol. 5: 195-202.

Response or Soft-Shell Clam Growth to Pollution

49

Brothers, E. B. 1979. Age and growth studies on tropical fishes.
Pages 119-136 in S. B. Saila and P. M. Roedel (eds). Stock
Assessment for Tropical Small-Scale Fisheries. International
Center for Marine Resource Development, Kingston. Rl.

Brown, R. S., R. E. Wolke, C. W. Brown & S. B. Saila. 1979. Hydro-
carbon pollution and the prevalence of neoplasia in feral New
England soft-shell clams, Mya arenaria. Pages 41-51 in F. M.
Peters (ed.), Animals as Models of Environmental Pollution.
National Academy of Science, Washington, D.C.

Cassie, R. M. 1954. Some uses of probability paper in the analysis
of size frequency distributions. Aust. J. Mar. Freshw. Res.
5:513-522.

Cloern, J. E. & F. H. Nichols. 1978. A von Bertalanffy growth model
with a seasonally varying coefficient. J. Fish. Res. Board Can.
35:1479-1482.

Dow, R. L. 1975. Reduced growth and survival of clams transplanted
to an oil spill site. Mar. Pollut. Bull. 6:124-125.

. 1978. Size-selective mortalities of clams in an oil spill site.

Mar. Pollut. Bull. 9:45-48.

& J. W. Hurst. Jr. 1972. Renewable resource problems of

heavy metal mining in coastal Maine. Maine Sea Shore Fish.
Res. Bull. 35:1-8.
. 1975. The ecological, chemical, and histopathological

evaluation of an oil spill site. Part I. Ecological studies. Mar.
Pollut. Bull. 6:164-166.
Eisler, R. 1977. Toxicity evaluation of a complex metal mixture to
the soft-shell clam. Mar. Biol. 43:265-276.

& R. J. Hennekey. 1977. Acute toxicities of Cd 2+ , Cr* 6 ,

Hg , Ni + , and Zn to estuarine macrofauna. Arch. Environ.

Contain. Toxicol. 6:315-323.
Fong, W. C. 1976. Uptake and retention of Kuwait Crude Oil and its

effects on oxygen uptake by the soft-shell clam, Mya arenaria.

J. Fish. Res. Board Can. 33:2774-2780.
Gallucci, V. F. & T. J. Quinn II. 1979. Reparameterizing, fitting,

and testing a simple growth model. Trans. Am. Fish. Soc. 108:

14-25.
Gerking, S. D. 1957. Evidence of aging in natural populations of

fishes. Gerontologia 1:287-305.
Gilfillan, E. S.. S. A. Hanson, D. J. Page, D. Mayo, J. Cooly, J. Chal-

fant, T. Archambeault, A. West & J. C. Harshbarger. 1977.

Comprehensive study of petroleum hydrocarbons in the marine

environment at Long Cove, Searsport, Maine. Final report to the

Department of Environmental Protection, Contract No. 906439.

192 pp.
Gilfillan, E. S., D. Mayo, S. Hanson, D. Donovan & L. C. Jiang. 1976.

Reduction in carbon flux in Mya arenaria caused by a spill of

No. 6 fuel oil. Mar Biol. 37:115-123.
Gilfillan, E. S. & J. H. Vandermeulen. 1978. Alterations in growth

and physiology of soft shell clams, Mya arenaria, chronically

oiled with Bunker C from Chedabucto Bay, Nova Scotia, 1970-

76. /. Fish. Res. Board Can. 35 :630-636.
Hampson, G. R. & E. T. Moul. 1977. Salt marsh grasses and #2 fuel

oil. Oceanus 20(4): 25 -30.
Hyland, J. L. & E. D. Schneider. 1976. Petroleum hydrocarbons and

their effects in marine organisms, populations, communities, and

ecosystems. Pages 436-506 in Sources, Effects and Sinks of

Hydrocarbons in the Aquatic Environment. Proceedings of a

conference held August 9-11, 1976. American institute of

Biological Sciences, Washington, D.C.

Kennish, M. J. & R. K. Ollson. 1975. Effects of thermal discharges
on the microstructural growth of Mercenaria mercenaria. Environ.
Geol. 1:41-64.

Macdonald, P. D. M. & T. J. Pitcher. 1979. Age-groups from size-
frequency data: a versatile and efficient method of analyzing
distribution mixtures. /. Fish. Res. Board Can. 36:987-1001.

Mayo, D. W., C. G. Cogger, D. J. Donovan, R. A. Gambardella,
L. C. Jiang & J. Quan. 1975. The ecological, chemical, and histo-
pathological evaluation of an oil spill site. Part II. Chemical
studies. Afar. Pollut. Bull. 6:166-171.

Mead, A. D. & E. W. Barnes. 1904. Observations on the soft-shell
clam (fifth paper). Pages 29-68 in Rhode Island Comm. Inland
Fish., 34th Annual Report.

Newcombe, C. L. 1936. A comparative study of the abundance and
the rate of growth of Mya arenaria L. in the Gulf of St. Lawrence
and Bay of Fundy regions. Ecology 17:418-428.

Ricker, W. E. 1975. Computation and interpretation of biological
statistics of fish populations. Bull. Fish. Res. Board Can. 191:
1-382.

Rosenberg, R. 1976. Benthic faunal dynamics during succession
following pollution abatement in a Swedish estuary. Oikos 27:
414-427.

Sanders, H. L. 1977. The West Falmouth oil spill-Florida, 1969.
Oceanus 20(4): 15-24.

. 1978. Florida oil spill impact on the Buzzards Bay benthic

fauna: West Falmouth. / Fish. Res. Board Can. 35:717-730.

. J. F. Grassle, G. R. Hampson, L. S. Morse, S. Garner-Price

& C. C. Jones. 1980. Anatomy of an oil spill: long-term effects
from the grounding of the barge Florida off West Falmouth,
Massachusetts. J. Mar. Res. 38:265-380.

Sickle, J. van. 1977. Mortality rates from size-distributions. Oecologia
27:311-318.

Shuster, C. N„ Jr. 1951. On the formation of midseason checks in
the shell of Mya. Anat. Rec. 1 1 1 :543.

Tanaka, S. 1962. A method of analyzing a polymodal frequency
distribution and its application to the length distribution of the
porgy, Taius tumiforms (T. and S.). J. Fish. Res. Board Can.
19:1143-1159.

Tesch, F. W. 1971. Age and growth. Pages 98-130 in W. E. Ricker
(ed.), Methods for Assessment of Fish Production in Fresh Waters.
Int. Biol. Program, Handbook 3. Blackwell Scientific Publica-
tions, Oxford.

Thomas, M. L. H. 1973. Effects of Bunker C oil on intertidal and
lagoonal biota in Chedabucto Bay, Nova Scotia. /. Fish. Res.
Board Can. 30:83-90.

. 1978. Comparison of oiled and unoiled intertidal com-
munities in Chedabucto Bay, Nova Scotia. /. Fish. Res. Board
Can. 35:707-716.

Vanderhorst. J. R., J. W. Anderson, P. Wilkinson & D. L. Woodruff.
1978. Estimation of effects from oil on intertidal populations:
experimental perturbations versus natural variaton. Pages 807-
820 in Proceedings of the Conference on Assessment of Ecological
Impacts of Oil Spills, 14-1 7 June 1978. American Institute for
Biological Sciences. Washington. D. C.

Vandermeulen, J. H. 1977. The Chedabucto Bay spill-Arrow, 1970.
Oceanus 20(4):31-39.

& W. R. Penrose. 1978. Absence of aryl hydrocarbon

hydroxylase (AHH) activity in three marine bivalves. J. Fish.
Res. Board Can. 35:643-647.

Journal of Shellfish Research, Vol. 1, No. 1, 51-55, 1981.

RECENT ADVANCES IN HARD CLAM MARICULTURE 1

J. L. McHUGH

Marine Sciences Research Center, 2

Slate University of New York, Stony Brook, NY 11794

ABSTRACT Failure to develop a satisfactory method of hard clam aquaculture, despite about 70 years of research, may
be based on faulty premises. There is no problem raising hard clams to market size under artificial conditions provided
adequate attention is given to care and to cleanliness. The only impediment is cost, which under present methods is too
high for economic gain. The flaw may be reliance on small numbers of clams, thinking millions are sufficient when billions
may be required to smother predation.

Another flaw may be lack of adequate law enforcement. Grounds must be patrolled constantly to keep out violators.
That means adequate coverage 24 hours a day, 7 days a week, and 365 days a year. It also means adequate support in the
courts so that the penalty for being caught is not worth the risk.

Experimental management of the grounds might be a better method. An area could be divided into three parts, keeping
one open and two closed -rotating the closed areas each year. If enforced adequately that would give sufficient protection
to seed clams, and the management plan could be adjusted accordingly as knowledge accumulates of local conditions.

INTRODUCTION

Interest in the possibility of growing hard clams (Mercen-
aria mercenaria) artificially has been evident in this country
for at least 70 years. Shortly after the turn of the century.
Belding (1909) advocated mariculture as a means of halting
overfishing and increasing the supply of clams. Kellogg
(1910) also believed that mariculture was the answer.
Beginning in the late 1930s, Loosanoff and Davis (1949,
1963), and their associates believed that mariculture was
feasible, and they developed many of the techniques on
which present-day artificial propagation is based. Carson
(1945) said that the fishery could be greatly developed by
extensive farming. Since that time many people have toyed
with the idea that artificial production of clams is feasible;
but to date I am not aware of any enterprise operating on a
consistently profitable basis. If it was, one would think that
such procedures would be routine by now, and that substan-
tial quantities of the hard-clam catch would be produced
by artificial means. But they are not.

What is the problem? Were the early enthusiasts too
optimistic in their views? Were there unexpected difficul-
ties not anticipated at first? Has development proceeded
too haphazardly, failing to capitalize upon earlier break-
throughs or failures? Which of those or other circumstances
have interfered with success? What are the prospects for
the future?

STATUS OF KNOWLEDGE

It is not necessary to go into great detail to show that
there is no insuperable handicap to rearing hard clams
under artificial conditions from fertilization of the egg to
metamorphosis, or to market size. Environmental conditions

'"The studies on which this paper is based were supported by grants
from the New York Sea Grant Institute and the National Oceanic
and Atmospheric Administration, United States Department of
Commerce.

2 Contribution 287, Marine Sciences Research Center.

are known; food requirements are understood; disease can
be controlled; and growth and survival are more than
adequate. The chief problem is the cost of doing all those
things. Production under artificial conditions to market size
is simply not financially feasible, even though growth under
ideal conditions can be several times faster than natural,
and survival is much greater.

Large quantities of eggs can be raised to metamorphosis
at acceptable cost, and some growth of young also is possible.
But at some stage, well before commercial size is reached,
juveniles must be transferred to the natural environment if
costs are to be held down. At the juvenile stage, clams are
highly vulnerable to predators, of which there are many,
and not enough survive to make the operation cost effective.

Mike Castagna. of Chincoteague Bay, has come closest
to solving that problem. He plants early juveniles in beds
covered with an appropriate layer of crushed stone aggre-
gate or other suitable material, provides baffles to cut down
the disturbing action of waves, and also fences to keep out
larger predators. He has been able to produce market-size
clams at a cost of about 2.2 cents each (in 1976 dollars
[Castagna and Kraeuter 1976]). That appears to be well
within the economic feasibility of clam growing, especially
since young clams are the most valuable and can be brought
to market size in about two years. Yet, despite this apparent
advantage there is no evidence that people in the industry
are rushing to try the method. In fact, it has been tried in
other places but with only limited success.

More recently. MacKenzie (1979) proposed that preda-
tion could be controlled easily by removing predators
mechanically and at a reasonable cost. His method seems so
simple that it is difficult to believe it is not already standard
procedure. MacKenzie pointed out that the method must
be demonstrated, must clearly be beneficial, that political
support must be stimulated, and that clam-production
specialists must guide the program until it is working
properly. In addition, MacKenzie suggested that other

51

52

MCHUGH

regulations including adequate protection of undersize clams
must be continued, which could be the least workable
portion of his method.

ENFORCEMENT

Enforcement of laws (or rather the lack of enforcement)
could be one reason for failure of all clam-management
plans. We cannot be sure of the reasons in other states, but
in New York there certainly is reason to doubt that laws are
being observed or enforced. It is most important that the
minimum size law, especially, be rigidly observed because
the basis of a clam-management plan is to assure an adequate
nucleus o\ spawners to provide recruitment of new stocks.
The present minimum size limit of one inch across the valves
probably is satisfactory. A sizable take of clams less than
one inch could have serious effects because the numbers of
eggs produced would drop rapidly. In 1976, when the catch
was only about 63% or less of the maximum, the lack of
adequate law enforcement at the present time could seriously
reduce the available brood stock.

In Great South Bay, where most of New York's clam
production is made, very few clams survive beyond littleneck
stage because harvesting is so intense (Greene 1978). When
production declines as it has in Great South Bay, and when
prices are high, there is considerable incentive to ignore the
cull law especially if law enforcement is inadequate. There
is no doubt regarding the laxity of present enforcement
(Mirchel 1980). Even if the laws are being applied well at
the harbormaster level, judges are notably easy on violators,
and may often reduce charges to lesser levels. It is not much
of a deterrent to a violator if he pays S25 for the privilege
of taking SI 00 or S200 or more worth of clams when there
is a reasonably good chance he may get away with it
altogether.

DIFFERENCES BETWEEN MAJOR CLAM SPECIES

The decline in clam landings of the major species has not
been significantly different. Hard-clam landings have dropped
from almost 20 million pounds in 1947, to about 7.2 million
in 19^9. a decline of about 63.9% (Figure 1). Soft-clam
landings have dropped from about P.4 million in 1939. to
about 8.3 million in 1979. a drop of about 52.4% (Figure 2).
Surf-clam landings have dropped from about 96.1 million
pounds in 1974, to 33.7 million pounds in 1979. a drop of
about 65% (Figure 3).

The main difference is the time it took to decline by
those amounts. Surf-clam landings took only five years to
show a decline. Surf-clam fishery history is shorter than the
other clam fisheries, not beginning as a major fishery until
after World War II. The hard- and soft -clam fisheries are
much older. Despite their apparently greater vulnerability,
they have taken much longer to decline from their peaks-
hard clam: 32 years, and soft clam: 40 years. Intuition
would suggest that just the opposite should have taken
place. Easily accessible in nearshore shallow waters, hard

and soft clams are taken with relatively inexpensive gear
and boats, are considerably more vulnerable to pollution,
and are subject to violation of laws, all of which would tend
to indicate that they would also decline more quickly. That
obviously was not so, and the question arises, why? An
answer to that question might help to correct some manage-
ment problems; but the answer is not clear. It is possible
that restrictions on inshore clamming, which some biolo-
gists and others have criticized as being unnecessary, have
actually helped. For example, hard- and soft-clams cannot
be taken with mechanical devices in most places. They must
be harvested with tongs, rakes, or by hand. Nonmechanical
harvesting is relatively easy on the bottom and usually does
not break large numbers of clams. Heavy dredges, however,
used on surf clams may break large numbers of clams,
especially young clams. Dredges may also bury large num-
bers of young, thus effectively destroying much of the
recruitment that otherwise could be available.

That difference is largely one of degree, however. Although
they have declined more slowly, hard and soft clams also

CO

Q

Z
Z)

o

Q_

U.
O

CO

z
O

z
yo

red.

^QL

QUJ

UJCL

(-

COCO

3t-

"3 Z

Q uj

<o

Figure 1 Commercial catch of hard clam Mercenaria mercenaria
aJong the Atlantic coast from 1929 to 1979. and the total value to
fishermen (adjusted by the consumer price index for all products).

Recent advances in Hard Clam Mariculture

53

50 60
YEARS

Figure 2. Commercial catch of soft clam Mya arenaria along the
Atlantic coast from 1929 to 1979. and the total value to fishermen
(adjusted by the consumer price index for all products).

have declined to less than half their peak levels. Hard clam
is seriously reduced in Great South Bay where it is more
abundant than anywhere else. There is no sign that the
situation will improve. Although the adjusted total value
of the hard-clam catch reached a peak in 1945, it did not
rise as high again until 1966. It reached an all-time peak
in 1972. and since that time has dropped to below the
1945 level. The adjusted total value of the soft-clam catch
rose to a peak in 1944, and did not rise as high again until
1969. The catch reached an all-time high in 1977, and since
has dropped slightly to about 93% of the 1977 level. It is
still considerably higher than in 1944. The adjusted total
value of the surf-clam catch reached a peak in 1977, and
has since dropped to about 60% of that level. What is the
best strategy for improving hard-clam production?

HARD-CLAM MARICULTURE

Apparently the bottleneck in growing hard clams under
artificial conditions lies somewhere between metamorphosis
and market size. Perhaps 4 or 5 mm is the lower limit, and
somewhere between 15 mm and 25 mm (about one inch) is
the upper limit. Within those size limits, costs are too great
to continue rearing clams in captivity, but clams that size
also are highly vulnerable to predation. It is not clear if
Castagna's method of growing juvenile clams under aggregate
with louvers and fences would be practical on a large scale
or applicable in different environments. People have tried
various methods in many places, but none have perfected a

YEARS

Figure 3. Commercial catch of surf clam Spisula solidissima along
the Atlantic coast from 1929 to 1979, and the total value to fisher-
men (adjusted by the consumer price index for all products).

reliable, replicable method. In fact, most experiments have
resulted in total failure. The reason for these failures may
be very simple and may represent a fatal flaw in thinking. It
simply may be that the numbers of clams used are so small
that the odds of having survivors are minimal. Let us
examine that possibility.

The largest number of seed clams produced in hatcheries
at the present is between 250 and 500 million. As far as 1
have been able to determine, the greatest number of clams
planted in one place in the natural environment was about
20 million. That sounds like a large number of clams, but
is it really? Considering the number of eggs produced per
clam, it is not. The largest figure, 500 million, could be pro-
duced by about 167 littlenecks or by about 83 cherrystone
clams according to figures carefully worked out by Bricelj
(1979). Those are not impressively large numbers. Allowing
a 20% mortality rate in the period from fertilization to
metamorphosis, that would only increase those numbers
five times.

Another way of looking at it would be to consider a
small section from the bottom of Great South Bay; for

54

\k Hugh

example, the Town of Islip's portion has about 20,000 acres.
Density of clams on the bottom varies greatly, but 4,750
clams per square meter appears to be about maximum for
small clams, and 160 clams per square meter for adults.
Over a large area containing various types of bottom, the
number of clams per square meter could be much less;
perhaps averaging one clam per square foot. For 20.000
acres, that would be about 870 million clams or an average
of about 54 bushels per acre, which is probably not far
from the true figure. If 20 million, 5-mm clams were planted,
it could be expected that predators would destroy at least
99 out of 100 the first year, leaving 200.000 clams. At a
conservative estimate. 50% of the first-year clams would
be destroyed during the second year, leaving 100.000. Only
under ideal conditions would those clams be large enough
to harvest at the end of the second year. That is only
(1 X 10 s )/(870 X 10 6 ) or 1 in 8.710 clams, again hardly
a large amount. If predators were present at the time of
planting and began eating immediately, they easily could
eat large numbers before the clams could dig in, thus
reducing the final yield further. If the clams must remain
on the bottom longer to grow to market size, the yield
would be less again. It appears that very large quantities
of small clams would have to be planted to assure an ade-
quate supply for harvesting. At present no hatchery is
raising the numbers of clams necessary to exceed the
capacity of predators to eat them all. except perhaps in
special areas where predators are low in abundance or
absent. The very fact of supplying additional small clams,
which are placed on the bottom unprotected and must dig
in. probably increases the likelihood that predators will be
there the next time.

Another way of looking at it is to consider the standing
crops of clams in a polluted area of similar characteristics.
say the New York portion of the Rantan Bay complex.
Campbell H%7) calculated that the standing crop in that
area was 291.200 bushels of littlenecks and 3.153,000
bushels of large clams, or 1 .05 clams per square foot. On
the 20.000 acres of bottom in Great South Bay. Town ol
Islip. that would equal Q 15 million clams. At 6 million eggs
per clam, that would total roughly 5.5 X 10 15 eggs. The
logistics of producing enough clams to add significantly to
that enormous basic production appears obvious. Our sights
must be raised considerably if we are to surpass natural
production.

The same can be said of the prevalent practice of bringing
in spawners from colder areas to extend the spawning season
and. thereby, to increase the odds that significant numbers
of eggs will survive. The impact of 1- or 2.000 bushels of
spawners is likely to be insignificant as compared with the
spawning potential of the clams already there. The cost of
bringing in enough spawners in good condition to have an
impact appears to be prohibitive, and the only benefit of
the present practice is to satisfy certain believers, thus
buying time for other more promising activities.

CAN OPTIMUM YIEUDS BE PRESERVED?

If yields cannot be improved economically by aquaculture,
what, if anything, can be done to at least preserve present
yields, and to possibly improve them to some extent? The
situation does not appear to be entirely hopeless, even
though on the average yields have been dropping for a long
time. The most effective way might be to experiment with
managing clam populations to find out what level of density
on the bottom would sustain the best harvest and, perhaps,
also what sizes ot clams. One way to do that would be to
establish an arbitrary limit below which a ground should
not be allowed to deteriorate. Just for the sake of argument,
the limit might be set at 30 bushels per acre. When a ground
drops to that level, it should be closed and thereafter be
monitored to see how quickly the stock rebuilds. That
obviously would be too complicated to manage if large
numbers of small sections of ground were handled in that
manner. It would be better to close fairly large strips at a
time, even if part oi a strip yielded more than the minimum
30 bushels. The simplest means, although not the only one,
would be to divide an area (for example, the bottom area of
Great South Bay. Town of lslip) into three parts; two of
which would always be closed and the third one open.
Those areas would then be rotated each year, so that one
part would be open every third year. That would be fairly
easy to patrol and to enforce, and the time sequence would
be about right for clams to become littlenecks in the natural
environment in most places. It would be well worth a try if
there were sufficient law enforcement personnel to be
effective; that is. a patrol boat in a closed area 24 hours a
day. 7 days a week. The potential of the clam harvest would
warrant that kind of surveillance.

CONCUUSIONS

It appears that the failure to develop a satisfactory
method of clam aquaculture, despite about ^0 years of
research, may be based on faulty thinking. There is no
problem in raising clams to market size under artificial
conditions provided adequate attention is given to care and
to cleanliness. The only impediment is the cost, which
under present methods, is too high for economic viability.
What may be the flaw in thinking is the reliance on small
numbers of clams, thinking millions are sufficient when
billions may be required to exceed the capacity of predators
to eat them.

Another fatal flaw may be the lack of adequate law
enforcement. Grounds must be patrolled constantly to keep
out violators, and that means adequate coverage 24 hours
a day. 7 days a week. 3t>5 days a year. It also means ade-
quate support in the courts, so that the penalty for being
caught is not worth the risk.

An alternative method might be to try experimental
management. One possibility would be to divide an area
into three parts, keeping one open and two closed, then
rotating the closed areas each year. If the closed areas

Recent Advances in Hard Clam Mariculture

55

were adequately patrolled by law enforcement personnel,
then the seed clams would be protected, and the plan could
be adjusted to provide optimum yields as knowledge
accumulated.

All three methods probably should he tried, and adjusted
as necessary to provide the best yields. That would be far
better than the present system, which is haphazard and not
notably successful.

references cited

Belding, D. L. 1909. A Report Upon the Mollusk Fisheries of
Massachusetts. Wright and Potter Printing Co., Boston. 243 pp.

Bricelj. V. M. 1979. Fecundity and related aspects of hard clam
(Mercenaria mercenaria) reproduction in Great South Bay,
New York. M.S. thesis. State University of New York, Stony
Brook. 98 pp.

Campbell. R. 1967. A report on the shellfish resources of Raritan
Bay, New Jersey. Proceedings of the Conference on Pollution of
Raritan Bay and Adjacent Interstate Waters. Third session.
Federal Water Pollution Control Administration, New York.
App. A:653-681.

Carson, R. L. 1945. Fish and shellfish of the middle Atlantic coast.
U.S. Dcp. Inter. Conserv. Bull. 38:1-32.

Castagna, M. & J. N.Kraeuter. 1976. The aggregate protection method
of culturing the hard dam, Mercenaria mercenaria. 10th European
Symp. Mar. Biol. Ostend, Belgium. Vol. 1:33 (abstract).

Greene, G. T. 1978. Population structure, growth and mortality of
hard clam at selected locations in Great South Bay, New York.
M.S. thesis. State University of New York, Stony Brook. 199 pp.

Kellogg, J. L. 1910. Shell-Fish Industries. American Nature Series.
Croup IV, Working with Nature. Henry Holt and Co., New York.
361 pp.

Loosanoff, V. L. & H. C. Davis. 1949. The spawning of quahogs in
winter and culture of their larvae in the laboratory. 1949 Con-
vention Addresses. National Shellfisheries Association: 58-66.

. 1963. Rearing of bivalve mollusks.Pp. 1-1 36 in F.S.Russell

(ed)., Advances in Marine Biology. Vol. 1. Academic Press, N.Y.

MacKenzie, C. L., Jr. 1979. Management for increasing clam abun-
dance. Mar. Fish. Rev. 41(10): 10-22.

Mirchel, A. C. F. 1980. Enforcement of hard clam laws on Great
South Bay, New York. M.S. thesis. State University of New York,
Stony Brook. 135 pp.

Journal of Shellfish Research. Vol. 1 , No. 1 , 57-67, 1981 .

OYSTER MARICULTURE IN SUBBOREAL (MAINE, UNITED STATES OF AMERICA)

WATERS: CULTCHLESS SETTING AND NURSERY CULTURE OF

EUROPEAN AND AMERICAN OYSTERS 1

HERBERT HIDU, SAMUEL R. CHAPMAN AND DAVID DEAN

Ira C. Darling Center for Research, Teaching and Service,
University of Maine at Orono, Walpole, Maine 045 73;

ABSTRACT This paper describes the development of cultchless setting and nursery culture techniques for European and
American oysters [Ostrea edulis L. and Crassostrea virginica (Gmelin), respectively] as adapted for the subboreal Maine,
United States of America, environment. For several years the University of Maine has functioned as a supplementary com-
mercial seed source and has evolved commercially workable techniques by a combined experimental and iterative approach.

Ideally, the Maine oyster culturist should receive a 10- to 20-mm seed oyster at the end of May to most efficiently take
advantage of the delayed but long-growing season. This may be achieved by starting the hatchery operation in late winter
with a complete dependence on cultured algae. The alternative is a seed-hatchery operation during the optimal summer
season necessitating development of overwintering techniques for very small cultchless oysters.

Initially in developing cultchless setting techniques, it was found that polished marble was highly stimulatory as a setting
surface. Unavoidable shell damage upon removal of the set and subsequent invasion of the protozoan Uronema marinum,
however, compelled the development of small particle substrate to procure the cultchless seed oysters, in the interest of
immediate production.

Several kinds of calcium carbonate particles were found that stimulated setting including tropical beach sand, forami-
niferal sand, marble chips, and mollusk shell chips. All larval setting techniques involved placing the particles in screened
boxes housed in recirculating water baths. Larvae were stimulated to set by increased water temperatures and by the
addition of adult oyster metabolites or extrapallial fluid.

Nursery culture of cultchless oysters to commercial seed (10 to 20 mm) proceeded in two phases. Early nursery culture
(to 2-mm size) was accomplished best in floating screened trays housed in recirculating water baths with cultured algae fed
commensurate with clearing rates. Late nursery to market size seed was reared best either in field rafts housing nested
screened boxes, or indoor stacked screened modules which could be operated either as open or closed systems. Culture gear
including some overwintering apparatus is described and illustrated.

INTRODUCTION

This is the first in a series of papers describing the devel-
opment of hatchery and growout techniques for European
and American oysters, Ostrea edulis L. and Crassostrea
virginica (Gmelin), respectively, on the subboreal Maine.
United States of America, coast. In 8 years of hatchery-
related research at the University of Maine, a purely experi-
mental approach has evolved into a production role for a
predictable supply of seed to commercial oyster culturists.
Resultant advances in techniques and gear innovations
reported herein should be useful to commercial hatcheries
in similar environments around the world.

In 1970 and 1971, it was found that hatchery-reared
cultchless oysters of both species performed exceptionally
well in many of the diverse estuarine environments of Maine
(Packie et al. 1976). Commercial use of hatchery-produced
cultchless seed was attractive because Maine lacks a con-
sistent natural-seed supply for either American or European
oysters. Availability of cultchless oysters, by air freight
from the west coast of the United States, further enhanced
the feasibility of a new Maine oyster industry at that time.
Through a modest extension program, Maine citizens were
encouraged to experiment with commercial culture using a
three-dimensional technique. By the mid-1 970's, over 100
persons were in various stages of experimentation with

1 Ira C. Darling Center Contribution No. 154.

several beginning commercial and pilot-commercial culture
operations. In 1976 and 1977, the west coast seed supplies
became unreliable compelling the University of Maine to
begin a commercial seed-production role to ensure that the
new Maine growout industry would survive and grow.

This subsidiary commercial role required that hatchery
research be viewed from an entirely different perspective,
i.e., from the view of a commercial operation trying to
develop a financially viable business. Because yearly demand
for seed oysters had increased to between 5 and 10 million
cultchless seed oysters, it was necessary to construct culture
gear and to innovate new techniques without benefit of an
adequate reserach base. Techniques that sufficed on an
experimental scale often were quite useless on a production
scale. Because equipment had to be built before the season
got underway, it was very difficult to change course in mid-
season if the gear or technique proved inadequate. Occasion-
ally crisis experiments were necessary to improve gear and
techniques for the following season. This situation, we
surmised, was very similar to that encountered by a new
commercial hatchery. If some production was to be main-
tained, time did not permit the luxury of more basic
but relevant research. Faculty and students, however,
developed research centered around the problems
encountered (Hidu et al. 1975, Packie et al. 1976, Hidu
et al. 1978, Plunket and Hidu 1978). Tins research, plus
improvements in gear and technique through a process of

57

58

HIDU ET AL.

iteration, led to significant advances in culture technology
particularly with European oysters.

Recently the seed-production mission was transferred to
three private entrepreneurs* in Maine. The real value of this
unusual University seed-production role is that significant
advances in culture techniques can be reported; similar
development accomplished privately would remain proprie-
tary. Presented here are integrated descriptions of cultchless
setting and nursery techniques that either incorporate
original research, employ significant gear innovations, or are
improvements on known hatchery techniques.

HATCHERY LOCATION

The University of Maine aquaculture facility is located at
Wentworth Point, midway on the Damariscotta River
estuary, in south-central Maine. The estuary is a narrow
drowned river mouth, properly a ria, approximately 24 km
in length. The selection of this site was dictated in part by
nonhatchery-related considerations, although the location
proved to be. for the most part, very favorable for a hatchery
operation.

Hydrography of the basin has been described by McAlice
(1977). At the Wentworth Point site, which has a 0.75 km
width and a 12-m depth, the estuary approaches a well-
mixed condition. Seawater from the Gulf of Maine moving
upstream at depth dominates the circulation. A mean tidal
height at Wentworth Point of 2.8 m produces currents up
to 1 m/sec, assuring excellent water circulation in field
nursery trays adjacent to the hatchery. Annual salinities
range between 27 and 33 ppt with only slight influence
from the freshwater Damariscotta Lake discharging 12 km
landward. Temperatures range from below 0.0°C (—1.8°
during January and February) to midsummer maxima of
17 to 18°C during July, August, and many times, into
September. The location is free of domestic, farm, or
industrial pollution and is relatively productive (Packie
et al. 1976); as much as 1.1 mg Carbon/L was fixed per
24 hr during the spring and late summer plankton blooms.
These blooms have been dominated by chain-forming
diatoms from the Gulf of Maine, most notably Skeletonema
costatum, Asterionella japonica, and Chaetoceros spp.
These algal species, however, were not useful as a supple-
ment for larval and early juvenile feeding; therefore, reliance
on cultured algae in hatchery operation has been necessary.

HATCHERY STRATEGY

Most Maine oyster growers prefer 10- to 20- mm seed in
late May or early June to allow best utilization of the
growing season which, in most areas, lasts from June to
November. There have been difficulties associated with

'Marine Bioservices Inc.. South Bristol, ME: Cozy Harbor Sea
Farms, Southport Island, Boothbay Harbor. ME; and Intertide,
Inc., Harpswell, ME.

smaller seed (< 10 mm), most importantly the need for
increased equipment and handling. If oysters have been
received late in the summer, the grower cannot take advan-
tage of the full growing season and the chances for over-
winter loss of small oysters increased. Growers should strive
to have the bulk of their seed reach a size of at least 25 mm
during the first season.

To produce seed oysters of a suitable size and at the
right time, the hatchery operator is faced with two alter-
natives, each with its advantages and disadvantages. The
first option is for an early season operation. It is possible
to produce 10- to 20-mm oysters in May by starting condi-
tioning of broodstock in late winter, i.e., February or March.
The advantage of this alternative is the short inventory
period from hatchery to sale, eliminating the need of risky
overwintering procedures. Disadvantages include the cost of
maintaining a seawater system during a difficult period,
costly heating of seawater, and, most importantly, the
absolute dependency on cultured algae for all phases of
hatchery and nursery operations. The other alternative
is a summer hatchery operation followed by a fall and
winter nursery period to producd seed oysters of the proper
size for the following spring. In Maine, conditions are
optimal for a hatchery operating during the summer;
hatchery systems are maintained easily; there is a minimal
need to heat seawater: natural broodstock conditioning is
advanced or retarded easily; and finally, natural algal popu-
lations are abundant for feeding the spat in the late mursery
phase. The drawback is that the seed stock must be over-
wintered before sale, and overwintering of small European
oysters is unreliable. If this element can be made secure,
we would opt for a strong summer hatchery progTam.

HATCHERY TECHNIQUE

Setting

Early experiments investigated the feasibility of using a
variety of substrates including glass, various plastics, and
polished granite, none of which was stimulatory to the
setting of .American and European oysters. Similarly, the
use of "Mylar" sheets (Dupuy and Rivkin 1972) did not
appear feasible because European oysters were not stimu-
lated to set, and the space and labor involved in incubation
of sheets to finally obtain cultchless oysters appeared
prohibitive in cost in a commercial application (Lipschultz
and Krantz 1978). Polished marble, which is largely calcium
carbonate, was found to be highly stimulatory to setting
larvae of both species (Hidu et al. 1975). However, very
large losses in the juvenile phase, described later, forced
abandonment of these techniques in favor of small calcium
carbonate particles in setting.

Other experiments investigated factors that might stimu-
late setting in mature European oyster larvae. Earlier work
with American oysters indicated that a waterborne pher-
mone from adult oysters stimulated setting of their larvae

Oyster Mariculture in Subboreal Waters

59

(Hidu 1969, Veitch and Hidu 1971). A concentrated source
of pheromone was found in extrapallial fluid (EPF); EPF
was utilized routinely in the setting process with American
oysters. With European oysters, however, Britisli workers
strongly contented that the "gregarious setting response"
was mediated by contact with specific compounds on the
setting surface (Crisp 1965. 1974; Bayne 1969). No material
stimulated metamorphosis in European oysters when added
in solution or suspension by the British. However, we felt
the surface chemistry versus waterborne pheromone mech-
anisms needed further study since the outcome could have
considerable bearing on our setting procedures.

Contrary to British findings, all our experiments indicated
stimulatory action of a waterborne pheromone in setting of
European oysters (Hidu et al. 1978). Initially, extensive
trials indicated that the addition of EPF in suspension was
stimulatory immediately to setting in European oysters. A
waterborne factor was demonstrated further by exposing
mature European oyster larvae to EPF prior to exposure to
cultch surface. The "pretreated" larvae then set at signifi-
cantly higher rates than untreated controls but significantly
lower than larvae in cultures that contained EPF and cultch
shell together. Thus evidence was obtained that European
oyster larvae would respond to metabolites in suspension
similar to American oysters. Ultimately, all of this informa-
tion was utilized in our hatchery setting procedures.

WORKABLE SETTING TECHNIQUES

By using 300-^m calcium carbonate particles and changing
nursery techniques, survival rates of mature larvae to 2 -mm
spat quickly rose from less than lOSc to over 50%. Small par-
ticle techniques are still being refined, but for the present,
the following has been the most workable method.

The objective has been to obtain a batch of uniform
mature larvae, the majority of which would set on the small
particles in a relatively short time . This has been accomplished
by grading larvae with stainless steel screens. Mature larvae
have been removed selectively using a sieve series of 70, 80,
and 90 meshes per inch. The larvae retained on the 70-mesh
screen should have the ability to set when stimulated to do
so. Metamorphosis should be delayed as long as possible
before putting the larvae into setting baths to ensure the best
response to the particles. This has been accomplished by
retaining graded mature larvae in 400-liter polyethylene
vessels before introduction into the setting baths. Polyeth-
ylene surfaces have not (in most cases) been stimulatory to
setting, especially to European oysters. An early workable
system utilized a 60-liter polyethylene vessel into which a
PVC -lined screened box was placed. Setting particles were
added to cover the screen to a depth of about 5 mm and
cultured algal foods were added in excess. The water was then
recirculated gently through the box with an air-lift system.
More recently, the screened boxes with larvae and chips were
merely inserted into the recirculating baths which also were
used for initial rearing of early juveniles (Figure 1).

In the setting baths conditions were manipulated to
obtain a massive set in as short a time as possible. Water
quality in the setting baths was maintained and the conver-
sion of larvae to spat maximized. Since it has been demon-
strated that adult waterborne oyster metabolites and
increased temperatures may stimulate setting in oysters
(Lutz et al. 1969), the water temperature was raised to
24 to 26°C; several liters of 1 jjni filtered seawater from the
adult oyster conditioning baths were added. With a vigorous
brood of larvae which have delayed setting, these conditions
produced a heavy set on the small particles within several
hours up to a day. The setting bath was then maintained
for several days with daily water changes until the spat
achieved a sufficient size to be screened away from the
300-jum particles. Spat reaching a diameter of 500 /Jin were
separated from the particles using a 50-mesh/inch screen.

Behavioral differences between American and European
oysters in setting have been noted; therefore, apparatus
and procedures had to be modified accordingly. For example,
European oysters were delayed easily in their metamorphosis
in polyethylene larval culture vessels, but American oysters
would set, en ?nasse, on the sides of the vessel almost
instantly. American oysters have a high tendency to set on
the sides of the PVC-lined box inserts, whereas European
oysters "seek out" the particles on the screens. Therefore,
it appeared necessary to have very shallow inserts for
American oysters or to construct the inserts of material
that was not conducive to setting. Adding a thin layer of
petroleum jelly to the sides of the inserts prevented setting
on the vessel sides and apparently was not detrimental to
the oysters. The two species have different preferences for
calcium carbonate particles. European oysters would set
well on a variety of particles including shell chips, marble
chips, tropical beach sand, and foraminiferal sand from
marine deposits. The American oyster was more selective,
with beach sand giving poor results. Overall, the European
oyster at setting was a more cooperative animal in the
hatchery than its American cousin.

NURSERY CULTURE

Cultchless oysters must be carefully nurtured to a size
that would allow a commercial grower to efficiently handle
the product . Originally, the culturists purchased a 3- to 6-mm
"window screen" size oyster; commercial growers, however,
experienced variable performance and handling difficulties
with the very small seed oysters. The optimal size salable
seed oyster was 10 to 20 mm. To achieve that size, the
hatchery-nursery system had to be divided into two or
three components: (1) an early nursery, entailing an indoor
controlled system to grow seed oysters from metamorphosis
to 2- to 3-mm size; (2) a late nursery, a controlled indoor or
outdoor system to produce 10- to 20-mm seed, and/or (3)
an overwintering procedure if small oysters were produced
late in the growing season.

60

HlDU ET AL.

\J/

Figure 1. Setting and early nursery dual tanks each with a 270-liter capacity.

Construction materials: 1.9 cm exterior plywood. 5.08 cm x
10.16 cm planks. 0.25 cm PVC sheet stock. PVC Sch 80 pipe,
PVC ball values, and plastic magntic drive pumps.

Construction: laminate the PVC sheets to the plywood sheets
before cutting plywood for the tank, eliminating cumbersome
procedure of fitting PVC sheets to tank interior. Weld all PVC seams
to ensure a watertight seal. Mount pump for each side behind tank
in a wooden enclosure for protection from salt spray.

Overall inside tank dimensions: 0.6 < 0.6 \ 1.8 m with enure
system resting on a 0.6 x 2.4 m plywood base.

Cost: approximately $250 per tank plus 25 hours labor for
construction using purchased materials for five dual units (1978
dollar value).

In use, the tank is tilled just below the PVC ball valves. Tank
water is drawn into the pump from a port location one-third the
distance from the bottom of the tank and is pumped to a manifold
at the top rear of the tank. Each tank is drained centrally. The
recirculating system, including pumps and piping, should be drained
and rinsed periodically with fresh water. On a regular schedule the

entire tank should be tilled with freshwater detergent or Clorox
mixture and recirculated for several hours to remove protozoan,
bacterial and algal Him buildup.

Tank inserts include (a) early design wooden PVC impregnated
setting boxes, and (b) floating PVC frames with mesh. Wooden boxes
were constructed of 1.27 cm exterior plywood painted with heavy
duty PVC cement. Bottoms were covered with 180 Nytex mesh
with a surface area of 2,173 cm and can accommodate 250,000
setting larvae. The newer floating frames were constructed of
3.8-cm PVC-OWV pipe, mitered and welded at the corners. These
were fitted with 180 N'ytex mesh when used as setting trays, or
fiberglass window screen when used for spat growth. The Nytex
mesh must be glued to the frames; the fiberglass window screen may
be welded on. A bead of clear silicone sealer was laid between the
inside mesh edge and the PVC frame to prevent larvae or spat
entrapment. Frames were built 2.5-cm smaller than inside dimension
of the tanks to facilitate handling. The PVC frames have a mesh
surface area of 3.825 cm" and easily accommodate 350.000 setting
larvae. These frames also may be used in conjunction with the spat
growing module described in Figure 3.

Oyster Mario/litre in Sebbori al Waters

61

Early Nursery Culture -Evolution of Technique

Cultchless oysters have to be nurtured up to the 2- to
3-mm size under closely controlled hatchery conditions.
New cultchless oysters were very fastidious in their food
requirements. The fine screens necessary for holding them
were very resistant to water flow due to a surface-tension
effect. Thus, an early outdoor placement was impractical,
whatever the season.

Nursery operations in the first 3 years suffered cata-
strophic losses of cultchJess spat, preventing any significant
hatchery production. Losses, in most cases, followed a
similar pattern. Spat (removed from polished marble and
placed under a variety of closed systems) were observed to
repair damaged shell edges readily and to grow rapidly until
an 0.8- to 1 .0-mm size was attained. Then the spat became
very transparent, ceased significant growth, and eventually
were lost in a mass mortality. A free-swimming ciliated
protozoan. Uronema marinum, and attached ciliates
f'orticella sp. and Zoothamnium sp. became epizootic
prior to and during the mortalities.

At the time, several probable causes for the losses seemed
apparent and. no doubt, the causes were interrelated. It
was apparent that uncoated fiberglass in a closed system
with 3 2-day period between water changes was marginally
toxic to spat. Further, severe damage to some spat removed
from the marble may have allowed buildup of ciliated
protozoan U. marinum populations (Piunket and Hidu 1978).
Although studies have indicated that U. marinum is entirely
a bacterial feeder, the protozoan readily entered healthy
appearing oysters and, in large numbers, probably con-
tributed to the oyster mortalities.

Cessation of oyster growth at intermediate sizes, in the
presence of sufficient food, suggested that food quality
was not a problem but that some other element (either
depleting or excessive) became limiting with the larger
oyster biomass in the tanks. Ammonia buildup or calcium
depletion also appeared possible, either of which would
affect oyster growth. The slowed growth rates contributed
to the eventual mass invasion of commensal protozoans;
thus, the protozoans became food competitors and, in
severe cases, appeared to prevent the oysters from feeding.

Because of these continued losses, and the urgent need
to produce large numbers of seed oysters as quickly as
possible, a change in approach became necessary. The
following simultaneous steps were taken in the nursery
system:

1. Change of cultchless setting procedure eliminating
the polished marble technique and utilizing small particle
technology.

2. Elimination of fiberglass and metal from all water-
contact surfaces in rearing modules.

3. Change of maintenance protocol to more frequent
changes with more coarsely filtered seawater. and the use
of redundant culture modules that had been purged with a
water-Clorox mixture during downtime.

With these new techniques, oyster survivals increased
dramatically to over 50%. At once, U. marinum became
rare in the cultures, and the epifaunal protozoa, although
always present in low numbers, never built up to epidemic
proportions.

Workable Early Nursery Techniques

Cultchless spat of either species at 0.5 mm size were
separated by screening from vacant 300-Mm particles in the
setting containers and placed on floating screens in a 270-
liter closed system (Figure 1 ). Initially, a 0.5 x 0.5 m screen
carried 250.000 new spat with the numbers reduced to
50.000 spat at 2 mm.

Baths were drained daily, and new seawater added was
coarsely bag-filtered to 10 £im and held at 25 ± 1°C for
both species. Spat were sprayed daily on the screens with
cold fresh water to reposition the oysters and to remove
as much particulate waste material as possible. On alternate
days the oysters were removed to a clean screen and placed
in a culture module purged wnh a water-Clorox mixture
during the previous 48 hours. Cultured algae Isochrysis
galbana, Monochiysis luthcri, and Cyclotella nana were
added daily at an initial rate of 8 x 10 10 cells per 250.000
spat. As the seed oysters grew, food demands increased to
several times the original amount. In all cases, the feeding
rate was varied commensurate with clearing rates of the
spat. A reduction in clearing rates from the previous day
was an indication of adverse conditions or loss of vigor of
the spat. The early nursery phase normally ended when the
spat reached 2 mm: about the same time we were no longer
able to meet the demand for cultured food. Larger culturing
facilities may find it advantageous to extend the early
nursery phase.

Late Nursery Culture

The late nursery stage began when daily food require-
ments of growing seed exceeded the ability to provide
them with cultured algae, and extended to the time optimal
salable size had been attained. If conditions were adequate
in the outdoor nursery area, the cultchless spat were placed
directly outside in floating invertible boxes (Hidu and
Richmond 1974,Gillmor 1978, Walker 1979), or in a rafted
tray culture module similar to that pictured in Figures 2a
and 2b. In either case, testing with small batches of seed
prior to a large placement was essential.

More research is needed to determine acceptable outdoor
conditions for early cultchless spat. An adequate algal
standing crop of the proper species with adequate salinity,
temperature, and current velocity are obvious necessities.
To illustrate the uncertainty of outdoor placement, in 1974.
a batch of 2-mm European oysters was placed in invertible
floating trays. Temperatures were 9°C in mid-May with a
verv apparent bloom of natural phytoplankton. The seed
oysters responded immediately, doubling and redoubling
their size in a short period time. In the following year,

HiDii r:T al.

The field module (Figure 2A) is constructed in two separate parts-the flotation collar-workdeck and
the inner submersed tray stacking frame. Workdeck is constructed of 2 x 4" and 4 x 4" spruce, 0.62 x
10.16-cm steel plate, and styrofoam flotation (2,475 kg). Overall dimensions are 2.14 x 0.46 x 6.71 m.
The inner stacking frame is constructed of 2 x 4", 4 x 4" and 2 x 8" spruce, 0.63 cm steel plate, 1.27-cm
steel rods, and 0.64 x 3.81-cm steel angle iron. Overall dimensions are 1.83 x 0.076 x 5.2 m. The inner
framework is divided into six bays constructed 1.27-cm larger than the 0.61 x 0.61-m wooden trays it
accepts. It is crossbraced and stiffened with 1.27-cm steel rods running from corner to corner, and others
running between the bays. There are four angle-iron brackets which hang from the inner framework and
act as self-locking stiffeners for the workdeck when the frame is bolted up into the floating workdeck.

The inner unit is removable to allow placement of spat on bottom during Maine winter-ice conditions.
Each bay in the submerged frame will accept 14 stacked trays. The top tray is a spacer to keep the stack
properly submerged; the bottom tray is fitted with stryofoam to provide a constant positive flotation
when the wooden trays are water sodden. With flotation on the bottom, the stacked trays behave much
like trays in a cafeteria tray dispenser. When the top tray is removed, the next tray will float and the
remainder continue to surface as the top trays are removed. Trays are constructed of 3.48-cm spruce,
3.48-cm galvanized epoxy-dipped lobster trap staples, and appropriate mesh sizes on two ends and on the
bottom of the tray. The upper and lower edges of the trays are rabbeted to provide positive locking of the
stacked trays and to help prevent small spat from being washed out by wave action. Nylon line (0.64 cm
diameter) looped about the tray stack and tied taut on the top easily secures the trays within the stack
preventing spat loss. This facilitates raising the stacks when the submerged tray framework is heavily fouled.

In the field, the complete module is positioned perpendicular (Figure 2B) to the prevailing current to
provide maximum water exchange in the trays. This unit is a highly stable work platform, and provides
ample work space with all the trays removed and stacked on deck for periodic air drying. Total cost of
the finished unit plus 200 trays was approximately S2,100 (1978 dollars). The unit requires 125 to 140
manhours of labor to assemble.

The field nursery unit has been in use for 5 years and shows only minor wear and rusting on the
flotation collar-workdeck. Underwater inspection of the submerged framework has revealed no appreciable
erosion or deterioration of the wood, and no noticeable corrosion of the steel rods. This unit is expected
to provide continuous service for at least 7 to 10 years.

Oyster Mariculture in Subboreal Waters

63

Figure 2A. Field module designed to accept stacked wooden trays to grow cultchless spat in an outdoor nursery environment.

Figure 2B. Field module positioned perpendicular to prevailing current.

64

HlDU ET AL.

however, with temperatures at 1 1°C and an apparent similar
bloom, a test group of European seed oysters did not grow and
eventually were lost. Therefore, the qualitative nature of the
phytoplankton bloom, i.e., presence of usable small forms,
may be crucial to the early field success of seed oysters.
Commercial growers also have noted this effect, reempha-
sizing the need for hatchery production of larger seed oysters.
A major problem with outdoor nursery culture in any
area is marine fouling of the tray mesh resulting in reduced
water flow and food transport. Provisions must be made
for redundant trays so that oysters can be transferred to
clean trays, thus allowing several days of air drying and
cleaning of the fouled trays before reuse. A system of
floating invertible tr3ys (Hidu and Richmond 1974, Gillmor
1978, Walker 1979) which allows periodic air drying also
is an effective method for reducing fouling of the small
tray mesh.

Overwintering

Successful overwintering of small seed oysters would
allow hatchery operations to be continued to the summer
season when the operations are most efficient. Studies, now
in progress, are defining an optimal overwintering procedure;
several helpful suggestions for optimal overwintering can be
offered. Initially, there appeared to be strong species differ-
ences in winter hardiness. Overwintering small (down to
5 mm) American oyster seed presented no problem regard-
less of condition. Small European oysters, however, did
present a problem. European oysters, whatever their size,
did not withstand prolonged periods of water temperature
below 0.0°C. Overwintering, either in a tempered laboratory
or in a more stenothermal oceanic situation, appeared
mandatory. Size of seed oysters was a factor. While over-
wintering large experimental batches of European oysters
in the Great Bay estuary. New Hampshire, Kevin Tacey
(personal communication) experienced high losses of seed
oysters below a 35-mm size; his larger size oysters suffered
little mortality. Late handling (December) also may be
detrimental because shell margins may be chipped when
the spat can no longer repair themselves.

Equipment for overwintering small European seed oysters
is under development (Figures 3 and 4). It may be possible
to hold large numbers of small seed oysters with slightly
tempered water temperatures and periodic, low-level feeding.
Preliminary results are encouraging but no definite recom-
mendations can be made at this time.

CONCLUSIONS

The development of cultchless setting techniques raises
important questions concerning the legal or proprietary
nature of the process. It is difficult to work with any
aspect without apparently infringing on patents which
often are broadly stated. If this situation is not resolved,
then the cultchless oyster may not achieve its potential
in marine food production.

The origin of the concept of cultchless setting, and
the legal right to patent the concept appear questionable.
The French appear to have originated the concept before
the turn of the century with naturally produced seed
oysters. Lime-coated tiles were placed in a spat-collecting
area throughout the summer and fall, and "cultchless
oysters" were procured during the winter months by
stripping the tiles. The French procured about 1 billion
cultchless seed oysters (0. edulis) in this manner annually
for use in their on-bottom growout beds (Bardach et al.
1972). The concept of procuring cultchless oysters in
the hatchery is attributed generally to William Budge of
Pacific Mariculture. Inc.. of California. U.S.A. (Budge 1970).
The Budge Patent No. 3,526,209 was filed on November 30,
1967, and patented, September 1. 1970. A second patent,
however, by Long Island Oyster Farms, Inc. (LIOF 1970)
was filed later on April 12, 1968, but patented earlier.
February 17, 1970. If both patents are valid, then one must
conclude that the concept of cultchless setting is not
patentable but specific approaches to the process are.

Although the processes and apparatus reported herein
were derived in a completely independent fashion, several
aspects of our methods appear to infringe on rather broadly
stated patents. For example, it is difficult, if not impossible,
to rear early cultchless oysters without housing the spat on
a screen and passing food-laden water through the screen.
Our nursery apparatus (Figures 1 and 3) depends on this
and yet the patents of Budge and LIOF both claim the
method. Similarly, our field-rearing module (Figures 2A
and 2B) depends on stacked screened cages secured in a
floating raft to allow algae-laden seawater to pass through.
But such an apparatus is specifically prohibited by Fordham
(1972), Patent No. 3.650.244. The floating invertible tray,
although we picture it (Hidu and Richmond 1974), and
mention it (Gillmor 1978) herein, has been patented by
Walker (1979). These interactions border on the ludicrous
and the ridiculous; however, the overall effect may be to
stifle all progress in cultchless oyster culture. It is literally
impossible to rear a cultchless seed oyster without infringing
on someone's broadly stated patent. Unfortunately, the
remaining problems with rearing cultchless oysters appear
not to be biological, but legal.

ACKNOWLEDGMENTS

The authors acknowledge the support of NOAA, Office
of Sea Grant, University of Maine at Orono, Project No.
R/A-l, and the financial support of the University of
Maine at Orono through Dr. Frederick E. Hutchinson,
Vice President for Research and Public Service. Mr. William
Bowers of Wiscasset, Maine, drafted the figures; Mr. Samuel
Chapman, the second author, originated many of the
concepts and constructed all of the culture gear pictured
herein. Dr. Malvern Gilmartin and Mr. Ronald Dearborn
added encouragement throughout the study.

Oyster Maricultcre in Subboreal Waters

65

Figure 3. Experimental module for overwintering smal] cultchless oyster spat.

Essentia! components of this unit consist of a series of stacked
trays housing floating PVC frames, dual holding tanks for particulate
settlement, degassing and algal food reservoir, and an apparatus to
operate the unit either as an open or as a closed system.

The stacked tray unit is constructed of 5.08-cm Sch 80 PVC pipe,
0.64-cm exterior plywood painted with floor enamel, various Sch 80
PVC fittings, and floating PVC framed screens as described in Figure 1 .
The structural frame for the trays consists of six 5.08-cm Sch 80
support legs, and fourteen 1.91-cm Sch 80 pipe sections welded onto
0.61 x 1.5 m rectangular frames and spaced 10.16 cm apart for
sliding the plywood trays. The 5.08-cm PVC legs also serve as the
water distribution and drainage mechanism. Threaded tees 5.08-cm
fitted with threaded plugs attach lo the bottom of the legs and allow
for watertight drainage plus the ability to level the entire unit by
adjusting the threaded plugs.

The painted plywood trays accept the PVC floating trays and
provide a water depth of 3.81 cm. The wooden trays are fabricated
from 0.64-cm exterior AB plywood, with pine sides nailed and glued
with a water-resistant glue, and painted with three coats of floor
enameL Inside dimensions of the trays are 4.45 x 52.68 x 85.09 cm.
The PVC welds between the 1.91-cm pipe and the 5.08-cm legs are
strong enough to preclude the necessity of cross bracing. This unit is
capable of handling 7 million oyster spat in the 1- to 2-mm range,
and 3 to 5 million spat in the 5- to 10-mm range.

During a flov. -through operation, seawater at the proper tempera-
ture enters tank A through 10 \Jra nylon filter bags Tank A overflows

through a standpipe into tank B. Residence time for both tanks is
12 minutes which is adequate for degassing when the AT is no
greater than 8 C above ambient. From tank B the water is pumped
through PVC piping into the leg manifold (C) of the stacked module.
Here water flow is adjusted to between 1 and 2 liters per minute
into each tray by 0.64-cm PVC ball valves. The stream of water flows
in diagonally, and drains from a portal opposite the entry point The
drains are 1.27-cm 90 male insert adapters that have had their
openings enlarged with a 1.27-cm drill. The 90 adapter is connected
to the drain leg by vinyl tubing which is secured to the drain leg with
a bored stopper. The drain support legs are connected to and empty
into a sump well (D).

During the feeding operation, the unit is operated as a closed-
recuculating system The mixed temperature water is shut off at
tank A. Algae is added to tank B through fill-line E. The water and
algae mixture follows path B-C-D-B. During this feeding phase,
the sump pump in well D pumps algae-laden water back into tank B.
By controlling the algal flow from E to B, specific feeding regimes
for specific times may be achieved with minimal algal wastage.

Cost of the PVC framework is about $280 plus approximately
40 hours of assembly time. The wooden trays cost about $7 each
including materials and labor: the floating frames cost $12 each. It is
recommended a minimum clearance of 10 cm be allowed between
wooden trays. This provides enough space to visually monitor the spat
without disturbance. Wooden trays are removed easily if a bottom drain
plug is included for draining prior to sliding trays from the module.

66

HlDU ET AL.

Figure 4. Universal laboratory module which allows advancement or retardation of conditioning broodstock or holds cultchless seed oysters
under ambient or a modified temperature regime.

This unit may be operated as a closed system in artificial feeding.
In that case, the catch basin acts an an ileal reservoir and the trays
are supplied by activating the recirculation pump.

The ambient seawater to this sytem is coarsely filtered through a
1-mm mesh to take advantage of natural phytoplankton production.
Water is piped to this unit through a 2.54-cm PVC drop-down.
Manifolds of 1.91-cm PVC then branch out horizontally across the
tray levels and deliver water through 0.64-cm PVC ball valves. The
ball valve openings have been drilled to 0.64 cm. and will deliver
4 liters per minute when water pressure is 4.5 to 5 psi. All of the
piping in this unit can be disassembled for periodic cleaning which
is mandatory under constant usage. This is accomplished by using
PVC unions which may be expensive initially but quickly pay for
themselves in time saved when cleaning the system.

The water temperature control may be attached to the end of
the module. A water-filled glass tube houses the copper temperature
probe near the bottom of the unit. The mixing tank holds 42 liters
of water and measures 0.3 x 0.3 x 0.45 m. The back is constructed
of 1.27-cm PVC stock, while the front and other sides are 0.64 cm
PVC sheeting. The corners of the tank are welded to form a sturdy,
watertight compartment. The 0.64-cm thickness will withstand
drilling and tapping for additional connections and drains. Tempera-
ture mixing is accomplished by the thermostat switching on and off

solenoids. One solenoid is always open and, at a water pressure of
4.5 to 5 psi. provides a constant flow of 81 liters per minute at
- 3 C. In the 26.5-liter trays, a lesser flow 1 1 liter per minute)
allows the temperature to be controlled within ± 0.25 C. Solenoids
are the dry type, no seawater touches the metal plunger which
valves the water. The body is nylon, the plunger diaphragm :s
neoprene. and the valving is "normally closed." Normally closed
solenoids stop water flow when deenergized. This assures "hat. in
the case of a power failure, experiments or animals fed by the
mixing tank will not be killed by high temperatures. All electrical
connections are made with watertight fittings to make the unit as
safe as possible. However, there is a measurable electrical leakage
from the metal solenoid core to the seawater ground.

Required maintenance of the mixing tank includes cleaning
the interior with hot fresh water whenever fouling is noticeable,
keeping the glass sensing bulb full with fresh water, and occasional
replacement of i solenoid coil or diaphragm. A 0.64-cm PVC ball
valve is threaded into the top of the mixing tank and serves as an
escape vent for gases evolved in heating water. One of these units
has been continuously used for 5 years with only occasional
replacement of component parts. Total cost of materials for this
mixing box was S140 in 1974, and at least 8 hours of assembly time
was required.

Oyster Mariculture in Subboreal WATERS

67

REFERENCES CITED

Bardach, J. E., J. H. Rythcr&.W. 0. McLarney. 1972. Aquacullure:

Vic Fanning and Husbandry of Fresh water and Marine Organisms.

Wiley Interscience, New York. N.Y. 868 pp.
Bayne, B. L. 1969. The gregarious behavior of the larvae of Ostrca

cdulis L. at settlement. J. Mar. Biol. Assoc. U.K. 49:327:356.
Budge, W. W. 1970. Method and apparatus for growing free oyster

spat. U.S. Patent No. 3.526,209.
Crisp, D. J. 1965. Surface chemistry, a factor in the settlement of

marine invertebrate larvae. Botanica Gothoburgensia III. Proc.

Fifth Marine Biol. Sym.. Goteburg. pp. 5 1-65.

. 1974. Factors influencing the settlement of marine

invertebrate larvae. Pages 177-265 in P. T. Grant and A. M.

Mackie (eds. ), Cheinoreccption in Marine Organisms. Academic

Press, London.
Dupuy, J. L. & S. Rivkin. 1972. The development of laboratory

techniques for the production of cultch-free spat of the oyster,

Crassostrea virginica. Chesapeake Sci. 13:45-52.
Iordham, E. C. 1972. Method and apparatus for protecting and

enhancing the growth of young shellfish sets. U.S. Patent No.

3,650.244.
Gillmor, R. 1978. Suspension culture of European oysters [Ostrca

edulis D.Proc. Nat. Shellfish. Assoc. 68:78 (abstract).
Hidu, H. 1969. Gregarious setting in the American oyster, Crassostrea

virginica Gmelin. Chesapeake Sci. 10(21:85-92.
. S. Chapman & P. W. Soule. 1975. Cultchless setting of

European oysters, Ostrca edulis, using polished marble. Proc.

Nat. Shellfish. Assoc. 65:13-14.
Hidu. H. & M. S. Richmond. 1974. Commercial oyster aquaculture

in Maine. Maine Sea Grant Bull. 2, IraC. Darling Center, Univer-

sity of Maine at Orono, Walpole, Maine. 59 pp.

Hidu, II., W. G. Valleau & F. P. Veitch. 1978. Gregarious setting in
European and American oysters-response to surface chemistry
vs. waterborne pheromones. Proc. Nat. Shellfish. Assoc.
68:11-16.

Lipschultz, F. & G. Krantz. 1978. An analysis of oyster hatchery
production of cultched and cultchless oysters utilizing linear
programming optimization techniques. Proc. Nat. Shellfish.
Assoc. 68:5-11.

Long Island Oyster Farms, Inc. 1970. Artificial rearing of oysters.
U.S. Patent No. 3,495.573.

Lutz, R. A., H. Hidu & K. G. Drobeck. 1969. Acute temperature
increase as a stimulus to setting in the American oyster, Cras-
sostrea virginica Gmelin. Proc. Nat. Shellfish. Assoc. 60:68-71.

McAlicc, B. J. 1977. A preliminary oceanographic survey of the
Damariscotta River estuary, Lincoln County, Maine. Maine Sea
Grant Technical Report 13. TR-13-77. Ira C. Darling Center,
Walpole, Maine. 27 pp.

Packic, R. L.. H. Hidu & M. S. Richmond. 1976. The suitability of
Maine waters for culturing oysters C. virginica and O. edulis.
Maine Sea Grant Technical Report MSG-TR- 10-76. Ira C.
Darling Center, Walpole. Maine. 22 pp.

Plunket, L & H. Hidu. 1978. The role of Uronema marinum
(Protozoa) in oyster hatchery production. Aquaculture
15:219-224.

Veitch, F. P. & 11. Hidu. 1971. Gregarious setting in the American
oyster Crassostrea virginica Gmelin. I. Properties of a partially
purified "setting factor." Chesapeake Sci. 12(3): 173- 178.

Walker. 1. 1979. Method of raising oysters. U.S. Patent No. 4,170,197.

Journal of Shellfish Research, Vol. l,No. 1,69-73, 1981.

USE OF LIPID-SPECIFIC STAINING TECHNIQUES FOR ASSAYING
CONDITION IN CULTURED BIVALVE LARVAE 1

SCOTT M. GALLAGER AND ROGER MANN

Woods Hole Oceanographic Institution
Woods Hole, Massachusetts 02543

ABSTRACT A simple, inexpensive, rapid technique for qualitatively assaying the nutritional status of bivalve larvae in
large-scale cultures is described and evaluated. Lipid has been identified as being the major energy reserve of developing
and metamorphosing larvae. Adverse culture conditions affect normal patterns of lipid accumulation and utilization. A
lipid-specific staining technique, using either Sudan Black B or Oil Red O, was used to monitor metabolic dysfunction and
larval health as related to culture conditions, and subsequently evaluated as a diagnostic tool for culture assessment.

In a series of matrix design experiments with larvae of the bivalve Teredo navalis Linne" [three temperatures: 10°, 20°,
and 30 C; and two food species, Isochrysis galbana (Parke) and Phaeodactylum tricornutum (Bohlin), plus relevant starva-
tion controls] , both temperature and food species were demonstrated to have profound affects on growth, on size of the
stained lipid reserve area of the digestive gland, and on the extent of lipid mobilization as indicated by the presence of
diffuse coloration in the tissues following staining. The high lipid content of healthy larvae and subsequent depletion during
imposed starvation periods were visualized with the staining technique and substantiated by comparative gross biochemical
analysis of actively growing and starved larvae.

The study concluded that the lipid staining technique could be used as a diagnostic tool for rapidly assessing condition
of cultured larvae.

INTRODUCTION

With the development of refined techniques for large-
scale culture of bivalve larvae by Walne (1956), and by
Loosanoff and Davis (1963), hatchery rearing of bivalve
seed offered a realistic option for restocking the depleted
natural supply of bivalve shellfish. Since that time hatchery
techniques have been modified and improved so that
excellent production usually can be expected (Dupuy et al.
1978). However, the inability to adequately control certain
parameters, such as state of broodstock or periodic changes
in water quality , and to predict the effects of such variability
on larval growth has led most hatchery operators to adopt an
array of larval-condition monitoring techniques. These
include shell growth rate, larval mortality rate, microscopic
examination of behavior, morphology, and disease signs
(Elston and Leibovitz 1 980). More involved assay procedures,
such as histological examination for tissue necrosis and respir-
ation rate measurements as an indicator of metabolic activity,
generally have been confined to research laboratories.

Lipid plays an essential energetic role in the normal
pattern of growth and metamorphosis in bivalve larvae
(see Holland 1978, for review). Helm et al. (1973) described
a direct relationship between total lipid content of newly
released larvae of the oyster Ostrea edulis L. and subsequent
viability and larval growth rate. These studies suggested that
continuous monitoring of total lipid content of larvae in
intensive culture systems could provide valuable information
concerning their general condition and relative metabolic
state (e.g., stressed, starved, or healthy). Techniques neces-
sary to effect such analyses are labor- and time-intensive,

Contribution No. 4772 from Woods Hole Oceanographic Institu-
tion, Woods Hole. Massachusetts 02543.

and require expensive equipment not found in average
hatchery operations. A simple and inexpensive technique
has been developed to qualitatively monitor both accumu-
lation of larval lipid reserves during normal growth and
changes in lipid distribution associated with adverse culture
conditions or environmental stress. The technique involves
staining subsamples of culture populations with a lipid-
specific stain and microscopic examination of whole larvae.

METHODS AND MATERIALS

A series of matrix experiments were designed to deter-
mine the effects of two environmental variables, tempera-
ture and food species, on growth and lipid accumulation in
larvae of the bivalve Teredo navalis L. Two species of uni-
cellular algae , Isochrysis galbana (Parke) and Phaeodactylum
tricornutum (Bohlin), were grown in semicontinuous
culture using the methods of Walne (1965) and Ukeles
(1973) on f/2 medium (GuiUard and Ryther 1962) at
20°C.

Nine groups of T. navalis larvae were grown in four
L-glass jars at an initial density of 1 larva/ml; seawater
(0.22 nm filtered) and food were changed at 2-day intervals.
Three of the nine groups were maintained at 10°C, three at
20 C, and three at 30°C. One group from each temperature
regime was fed I. galbana at a density of 5 X 10 4 cells/ml,
one was fed P. tricornutum at the same density, and the
third was maintained in the 0.22 pirn filtered seawater with
no food additions (hereafter termed starved).

At each change of seawater and food, subsamples of
approximately 100 larvae were removed from each of the
nine groups. These were, in turn, narcotized by a modifi-
cation of the method of Turner and Boyle (1974), and
stained specifically for lipid with either Sudan Black B

69

70

Gallaglr and Mann

(C.I. 26150) or Oil Red O (C.I. 26125) by the procedure
outlined below. After staining, the shell length and height,
and the diameter of the stained digestive gland area were
recorded for 30 individuals from each group. Larvae repre-
senting the mean of both parameters were photographed at
a magnification of 250X with high contrast black and white
film (Kodak Technical Pan 2415) to accentuate the stained
material.

Procedure for Narcotizing and Staining Bivalve Larvae

I. Narcotizing and Fixing

A. Pipet larvae (10 to 1000) into 6 ml vial or small
petri dish with ~ 2 ml seawater.

B. Add 2 drops 7.5 MgCl 2 solution, wait 5 minutes;
add 1 ml MgCl 2 , wait 5 minutes; add 2 ml MgCl 2 ,
wait 5 minutes.

C. Remove fluid leaving larvae on bottom— replace
with MgCl 2 .

D. Test state of larvae by pipetting a few into 10%
buffered formalin, when ready (i.e., larvae do not
contract), add ~ 5 drops formalin.

II. Preparation of Stain

A. Dissolve 0.75 g Sudan Black B (C.I. 26150) or
Oil Red O (C.I. 26125) in 100 ml ethylene
glycol heating to ~ 60°C.

B. Filter hot through Whatman no. 2 paper and
refrigerate, filter again when cool.

III. Staining for Lipid

A. Allow larvae to settle from step ID, remove all
fluid leaving larvae on bottom.

B. Add ~ 1 ml Sudan Black B or Oil Red O solution
and stain for a minimum of 1 hour.

C. Pipet off stain solution and add pure ethylene
glycol (~ 1 ml) to clear excess stain.

D. Let stand for a minimum of 30 minutes for Oil

Red O or for 4 hours for Sudan Black B (large
larvae in Sudan Black B may require up to
24 hours to clear).

E. Pipet off discolored ethylene glycol and replace
with pure ethylene glycol; clearing is completed
when excess stain ceases to color the medium.

F. Observe and photograph/mount in viscous medium
(e.g., glycerol jelly).

The narcotization procedure is not absolutely necessary
to achieve desired results but does increase the potential for
localizing lipid droplets in the velum. If necessary, larvae
may be left in 10% buffered formalin (step ID) for a few
days prior to staining. There is no maximum time for the
staining procedure (step IIIB) since ethylene glycol should
not alter gross lipid distribution (Humason 1962). Further
information for obtaining permanent whole mounts of larvae
may be found in Humason (1962).

Tissues surrounding the digestive gland remained stained
after a prolonged clearing period of up to 48 hours for some
groups. This diffuse coloration of the tissues did not photo-
graph well with black and white film making it necessary to
note the coloration present while observing through the
microscope.

Quantitative data for total lipid levels of T. navalis larvae
grown at 20°C and fed /. galbana with subsequent 3-day star-
vation periods were determined colorimetrically on groups
of 1,000 to 2,000 freeze-dried larvae after chloroform-
methanol extraction using the method of Marsh and
Weinstein(1966).

RESULTS

Prior to feeding, the straight hinge stage larvae contained
many small lipid droplets spread throughout the tissues with
a major concentration at the base of the velum (Figure 1).
Upon starvation, these disappeared gradually over a period

NOT STAINED

STAINED

Figure 1. Newly spawned larvae of Teredo navalis (0 days), starved for 3 days (starved), and either preserved in formalin (not stained) or
stained with Sudan Black B (stained). Larvae after 4 days of feeding (4 days) and a subsequent 3-day starvation period (starved).

Lipid Staining techniques eor Bivalve Larvae

71

of a few days, while the area surrounding the digestive gland
became more heavily stained as growth continued.

Sudan Black B worked especially well for young larvae
and was retained in the tissues for a longer period of time
than Oil Red O. However, if microscopic examination of
the larvae was possible within a few days of staining and
color photographs were to be taken, then the visually
striking bright-red coloration of the lipid droplets produced
by Oil Red was far superior to the coloration obtained
with Sudan Black B.

Shell growth was poor at 10°C regardless of the food
species, and greatest at 30°C when /. galbana was the food
source (Figure 2). The diameter of the darkly stained area
representing the digestive diverticula increased with growth
of the larvae at both 10° and 20°C (Figures 2 and 3).
Larvae fed either /. galbana or P. tricornutum at 10°C
accumulated large lipid reserves relative to their shell size.
There was no major accumulation of lipid at 30° with either
food species. Dispersed tissue coloration was present in all
starved larvae at 20°C and 30°C, in larvae fedP tricornutum
at 20° and 30°C, and in larvae fed /. galbana at 30°C.

Quantitative analysis of total lipid levels of T. navalis
larvae grown at 20°C on /. galbana revealed a steady increase
in lipid level throughout development, reaching a maximum
of 0.12 jug lipid/larva at the pediveliger stage (Figure 4).
Obvious decreases in total lipid level occurred at each
developmental stage when 3-day starvation intervals were
imposed.

DISCUSSION

The variable culture conditions and subsequent larval
growth encountered in any bivalve hatchery system neces-
sitates the use of condition indicies throughout larval
development. Since all of these indicies (e.g., growth rate,
mortality, disease signs, etc.) are essentially post facto in
nature, the culturist has little real-time control over prob-
lems that may arise during development. It is possible
that the normal pattern of storage and utilization of bio-
chemical components concerned with energy metabolism
would be influenced by adverse culture conditions. If the
progression of this dysfunction could be monitored on a
routine basis with a simple assay then such a technique
could be used as a diagnostic tool for early reparative
measures.

The biochemical component utilized during times of
energetic imbalance in invertebrate larvae has been identi-
fied as lipid rather than protein or carbohydrate because it
is the most abundant and easily mobilized storage material
(Holland 1978). Helm et al. (1973) concluded that healthy
adult oysters (Ostrea edulis), fed a food supply supplemented
with phytoplankton during conditioning, produced more
viable larvae, with higher lipid levels, upon release at the
straight hinge stage than those oysters whose diets had not
been supplemented. Millar and Scott (1967) also have shown
that larval lipid levels were dramatically reduced within a

few days when newly liberated O. edulis larvae were starved.
These results were visually reproduced in this study with
shipworm larvae indicating that the present lipid staining
technique could be used to make viability judgments on
newly spawned larvae as well as throughout larval
development.

200-

100 -

to

+1

E

&

UJ

X

200-

100 —

100 —

70S 15 2

2 3i3 4

ISOC HRYSIS

i 1 T

9*12 3
8*3

2 OS I 7

24? 7 3

PHAEODACTYLUM

"i 1 T

STARVATION

10 20 30 40 50

DAYS FROM FERTILIZATION

Figure 2. Shell growth of Teredo navalis larvae at three temperatures:
IOC (■), 20 C ( A ), and 30 C (•) on two food species and a starva-
tion control. Bars represent 1 standard deviation (SD). Numerical
values are the mean ± SD of the diameter of the darkly stained area
of the digestive diverticula at various stages of development (N = 30
for each value).

Bayne (1965) observed that large numbers of oil droplets
began to appear at the onset of metamorphosis in Mytilus
edulis larvae. When metamorphosis was delayed, these
droplets gradually disappeared. A similar pattern occurred
during periods of starvation. The author suggested that this
could represent an important food supply during times of
stress and metamorphosis. Culliney (1975) observed clusters

72

Gallager and Mann

I 0'

2

3

■- © & & © ft & O

2 day*

Figure 3. Three stages of Teredo navalis larvae fed hochrysis galbana (I), Phaeodactylum tricornutum (P), and starved (S) grown at three
temperatures. All larvae were stained with Sudan Black B (i: , died; bar = 200 Ltm).

0.05 —

0.0 1 —

~o\

/A

•-•

I ' 1 ' 1 ■ I

O 10 20 30

DAYS FROM FERTILIZATION

40

Figure 4. Total lipid levels of Teredo navalis larvae fed hochrysis
galbana at 20 C before (•) and after (O) a 3-day starvation period.
Arrow indicates 50% of population attained functional pediveliger.

of "transparent globules" in umbo stages of Teredo navalis
surrounding the digestive gland. The 10 to 20 /jm globules,
thought to be important food reserves, were equivalent in
size to the lipid droplets described in this study. Other mol-
luscan larvae have similar patterns of reserve accumulation.

Fretter and Montgomery (1968) noted the increase
in size and darkening in color of the digestive gland of
prosobranch veligers throughout growth and development.
They suggested that this could be used as an index of feeding
because varying color regimes were produced in the gland
with different diatoms in the diet.

The diffuse tissue coloration and relatively small digestive
gland area observed upon staining larvae grown at high
temperatures, fed P. tricornutum or starved, could represent
a shift in the pattern of lipid storage. These forms of stress
may necessitate mobilization of stored energy reserves into
the tissues surrounding the digestive gland to meet imposed
metabolic demands. Conversely, larvae grown at low tempera-
tures retained relatively greater quantities of lipid in the
digestive gland area, presumably due to decreased energetic
costs. Elston et al. (1981) have shown that the normal
pattern of lipid accumulation and utilization was disrupted
in the larval disease "vibriosis". Staining subsamples of large
cultures specifically for lipid could be used to test for early
signs of this disease; staining will show an abnormal dis-
tribution of lipid droplets in the digestive diverticula (R. L.
Elston, Cornell University, personal communication).

The present staining technique illustrates gross lipid
accumulation and depletion in relation to environmental
variables. These results have been substantiated by total
lipid analysis. It may be possible to employ this method as
a diagnostic tool for determining food quality, larval
condition, and potential for rapid growth in large-scale
bivalve cultures.

Lipid Staining Techniques eor Bivalve Larvae

73

ACKNOWLEDGMENTS

The authors express their gratitude to Mr. Bradford C.
Calloway for his advice concerning the larval narcotization

procedure, and to Ms. E. M. Lynch for typing the manu-
script. This investigation was supported by the Office of
Naval Research, contract N00014-79-C-0071 and
NR 083-004.

REFERENCES CITED

Bayne, B. L. 1965. Growth and delay of metamorphosis of the
larvae of Mytilus edulis (L.). Ophelia 2:1-47.

Culliney, J. L. 1975. Comparative larval development of the ship-
worms Bankia gouldi and Teredo navalis. Mar. Biol. 29:245-251.

Dupuy. J. L.. N. T. Windsor & C. E. Sutton. 1978. Manual for design
and operation of an oyster seed hatchery. Va. Inst. Mar. Sci.
Tech. Rep. No. 142. 109 pp.

Elston, R. L. & L. Leibovitz. 1980. Pathogenesis of experimental
vibriosis in larval American oysters, Crassostrea virginica. Can. J.
Fish. Aquat. Sci. 37:964-978.

, D. Relyea & J. Zatila. 1981. Diagnosis of vibriosis in a

commercial oyster hatchery epizootic, a case history. /. Shellfish
Res. 1(1):113 (Abstract).

Fretter, V. & M. Montgomery. 1968. The treatment of food by
prosobranch veligers. /. Mar. Biol. Assoc. U.K. 48:449-520.

Guillard, R. R. L. & J. H. Ryther. 1962. Studies on marine plank-
tonic diatoms. I. Cyclotella nana Hustedt and Detonula
confervacea Cleve. Can. J. Microbiol. 8:229-239.

Helm, M. M., D. L. Holland & R. R. Stephenson. 1973. The effect
of supplementary algal feeding of a hatchery breeding stock of
Ostrea edulis L. on larval vigour. J. Mar. Biol. Assoc. U.K. 53:
673-684.

Holland, D. L. 1978. Lipid reserves and energy metabolism in the
larvae of benthic marine invertebrates. Pages 85-1 23 in P.C. Malins

and J. R. Sargent (eds), Biochemical and Biophysical Perspectives

in Marine Biology. Academic Press, London and New York.
Humason, G. L. 1962. Animal Tissue Techniques. W. H. Freeman

and Co., San Francisco, California. 468 pp.
Loosanoff, V. L. & H. C. Davis. 1963. Rearing of bivalve molluscs.

Adv. Mar. Biol. 1:1-136.
Marsh, J. B. & D. B. Weinstein. 1966. Simple charring method for

determination of lipids. J. Lipid Res. 7:574-576.
Millar, R. H. & J. M. Scott. 1967. The larva of the oyster Ostrea

edulis during starvation. J. Mar. Biol. Assoc. U.K. 47:475-484.
Turner, R. D. & P. J. Boyle. 1974. Studies of bivalve larvae using

the scanning electron microscope and critical point drying.

Bull. Am. Malacol. Union Inc. 1974:59-65.
Ukeles, R. 1973. Continous culture-a method for the production of

unicellular algal foods. Pages 233-254 in Janet R. Stein (ed.),

Handbook of Phycological Methods. Cambridge University Press,

Cambridge, Massachusetts.
Walne, P. R. 1956. Experimental rearing of the larva of Ostrea edulis

L. in the laboratory. Fish. Invest. Ser. II Mar. Fish. G.B. Minist.

Agric, Fish. Food No. 20. 23 pp.
. 1965. Observations on the influence of food supply and

temperature on the feeding and growth of the larvae of Ostrea

edulis L. Fish. Invest. Ser. II Mar. Fish. G.B. Minist. Agric, Fish.

Food No. 24. 45 pp.

Journal of Shellfish Research, Vol. 1, No. 1, 75-81, 1981.

NITROGEN BALANCE OF JUVENILE SOUTHERN QUAHOGS (MERCENARIA
CAMPECHIENSIS) AT DIFFERENT FEED LEVELS 1 ' 2

B. B. GOLDSTEIN 3 AND O. A. ROELS

University of Texas, Port Aransas, Texas 78373

ABSTRACT A Tahitian strain of Isochrysis sp. was grown in outdoor continuous culture and fed at four different cell
densities to juveniles of the southern quahog clam Mercenaria campechiensis (Gmelin). Those cell densities were: 1x10,
5 x 10 , 1 x 10 , and 5x10 cells/ml. Controls consisted of trays without animals receiving an inflow cell density of
5x10 cells/ml, and trays with animals, but receiving only filtered seawater. Duplicate populations of 100 animals received
each treatment; each population had a whole wet weight of 10 g. The total flow rate to each population was 120 ml/min.

Incoming filtered seawater, incoming algal culture, and effluent from each shellfish population were collected daily and
analyzed for nitrite, nitrate, ammonia, urea, dissolved free amino acids (DFAA), soluble protein, total dissolved nitrogen,
and particulate protein nitrogen (PPN).

A nitrogen balance for juveniles ofM. campechiensis in a continuous flow system was calculated; 85 to 95% of all total
incoming nitrogen was accounted for in the different treatments.

Change in concentration of the various nitrogen-containing compounds as a result of passage through the shellfish
culture containers is described. Only those populations receiving an inflow algal protein concentration of 5.75 jUgat PPN/1
showed a significant excretion of ammonia. Any excretion of DFAA or urea was absorbed by microorganisms present in
the shellfish culture containers. Both nitrite and nitrate were absorbed by algae present in the copious biodeposits of
shellfish populations receiving an inflow algal protein concentration of 56.01 /Llgat PPN/1, and a significant uptake of
soluble protein by shellfish populations receiving ^5.75 £lgat PPN/1 was noted.

INTRODUCTION

The successful cultivation of bivalves requires control of
the reproductive cycle of the organism and knowledge of its
environmental and nutritional requirements. This latter
criterion requires investigating the best type(s) and amounts
of food. Criteria for determining the best type and/or
amount of food include growth, feeding rate, food chain
efficiency, ecological efficiency, protein conversion effi-
ciency, and condition index.

These criteria help to determine the best feeding regime
for the organism, but may not indicate the best feeding
regime insofar as the total culture system is concerned. No
organism can be cultured without regard to its role in the
culture system. If a particular food type is difficult and/or
expensive to grow, it may not be the best food organism to
use in the culture system, even though it may be very
nutritional for the bivalve. A particular food density that
is optimal for growth of the bivalve may result in the
excretion of toxic ammonia.

For these reasons, a complete study of the nutritional
requirements of a bivalve being considered for intensive aqua-
culture must take into account the role of the animal in the

This work was supported by the Caesar Kleberg Foundation for
Wildlife Conservation. B. B. Goldstein was the recipient of a fellow-
ship from the Jessie Smith Noyes Foundation.
University of Texas Marine Science Institute Contribution No. 000.
Present address: Systemculture Corporation, 828 Fort Street Mall,
Suite 610, Honolulu, Hawaii 96813.

managed food chain. One must determine how a culture
system affects the bivalve and how the bivalve affects the
system.

An excellent way to gauge those affects is by constructing
a nitrogen balance of the entire managed food chain. A
nitrogen balance should be constructed because: (lj nitrogen
often is the limiting nutrient of the growth of the primary
trophic level (Ryther and Dunstan 1971), (2) nitrogenous
waste products of the bivalve can be toxic to the animals
themselves or to other organisms downstream, (3) these
nitrogenous waste products may be used for the growth of
macrophytes, and (4) the production of animal protein
is often the primary goal of such managed food chains.

An important byproduct of studying nitrogen dynamics
of bivalves in a continuous-flow, managed food chain is
understanding the role of bivalves in the nitrogen cycle
of their natural environment. The results of such a study
may not be as realistic as a field study, but is more con-
trollable and subject to more intensive investigation, i.e.,
studying the effect of varying different elements of the
biotic and abiotic environments of the animal. Those
studies in which a small number of clams were unfed for
24 hours prior to the experiment, placed into a small bowl
of static, synthetic seawater, and the change in concentration
of different nitrogen compounds measured in the medium.
may be even more controlled and precise than studies
involving a continuous-flow, managed food chain. However,
they are so far removed from "real" life as to render the
results interesting but almost irrelevant.

A continuous-flow, managed food chain perhaps is the
best method to use to study the physiological responses of
an organism to biotic and abiotic factors of its environment.

75

76

Goldstein and Roels

Field studies can raise questions and validate the results of
studies in managed food chains.

A nitrogen balance was constructed for juveniles of
Mercenaria campechiensis (Gmelin) that were fed Isochrysis
sp. at different densities. Juveniles were used because little
is known of the bioenergetics and nitrogen cycling of
juvenile shellfish, and the greater growth rate of juveniles
resulted in more measurable growth in a shorter period of
time. The increased metabolism of juveniles resulted in
more measurable changes in various physiological responses,
such as ammonia excretion, in a shorter period of time.
Mercenaria campechiensis was used because little informa-
tion is available in the literature on its growth and physiology,
although the clam is abundant along the Gulf coast. Its
growth is usually faster than that of the northern quahog
Mercenaria mercenaria (Linne), or their reciprocal hybrids;
it is more tolerant to high temperatures than M. mercenaria.

MATERIALS AND METHODS

Algae

The alga used in this study is a Tahitian strain of Iso-
chrysis (T. Iso.) obtained from Dr. K. C. Haines of the
St. Croix, U.S. Virgin Islands, Artificial Upwelling Project.

The algae were grown in outdoor continuous culture at
the Port Aransas Marine Laboratory on the Texas Gulf
coast during October through November 1978, at a daily
turnover of 0.4. Guillards' F medium was used to enrich
the incoming 1 ^-filtered seawater to a level of 150 /Jgat
N0 3 - N/L.

Shellfish

Brood stocks were collected in an intertidal area of
Redfish Bay, an estuarine area between the mainland and
the barrier islands of the Texas Gulf coast near Corpus
Christi, in late February 1978. The clams were kept in the
laboratory for acclimation and gonad ripening, and were
fed T. Iso., exclusively. Spawning was induced by thermal
shock and the addition of stripped gonad suspensions. The
experimental animals were the progeny of one female and
two males. The larvae were fed a variety of phytoplankton
species including T. Iso. , Chaetoceros sp., and others.
There was no mortality after spat settlement indicating that
water quality was good and that T. Iso. (fed exclusively
after spat settlement) was a good food for juveniles of
M. campechiensis.

Prior to the experiment, 1,100 clams with shell lengths
of 7.62 ± 0.4 mm were divided into 1 1 groups of 100 each.
The average whole wet weight of each of those groups was
10.2 g ± 0.01. Group 11 was used to determine the shell
length, whole wet weight, and protein content of the
other experimental groups.

Each experimental group was kept in round plastic bowls
with tapered sides. Top and bottom diameters were 14 cm
and 10 cm, respectively. A plastic standpipe in the center of

each bowl maintained the water level at a depth of 4 cm for
a total volume of 250 ml. The inflow of cultured algae and/
or filtered seawater created a vortex in the containers
ensuring thorough mixing. The clams were spaced evenly
on the bottom of each bowl. Each group received a contin-
uous flow of 1 /i-filtered seawater and/or cultured algae as
indicated in Table 1 .

TABLE 1.

Flow rates and cell densities of experimental treatments.

Corresponding

Algal

Filtered

Inflow Algal

Culture

Seawater

Cell

Protein-N

Flow

Flow

Density

Concentration

Treatment

(ml/min)

(ml/min)

(cells/ml)

Otgat/I)

1

120

5 x 10 s

56.0

2

24

96

1 x 10 s

11.3

3

12

108

5 x 10 5

5.7

4

2.4

117.6

lxlO 4

1.3

5

120

Two replicate populations were utilized for each treat-
ment. Treatment 5, the control, received filtered seawater
only. Another control, which consisted of an identical
experimental setup but no clams, received 5 x 10 4 cells/ml
(Figure 1).

Experimental clams were kept in the dark throughout
the experimental period. Water temperatures ranged from
23° to 28°C, and salinities from 25 to 29 ppt during the
4-week experiment.

At the end of each week, the clams were removed from
their containers, blotted dry, and each group weighed after
the effluents from each clam group had been taken and
flow rates checked. The groups were then culled back to
their starting whole wet weights, and the remaining clams
returned to the experimental culture containers. The culled
clams were frozen for later analysis.

Biodeposits or tank deposits from the experimental
containers were removed and stored for later analysis prior
to returning the clams.

ANALYTICAL METHODS

Cell Densities

Cell densities were measured with a Speirs-Levy eosino-
phil counter.

Particulate Protein Nitrogen (PPN)

The method of Dorsey et al. (1977) was modified for
use with the Auto Analyzer II. The auto analyzer (AAII)
dispensed IN phenol reagent and absorbance was read on
the AAII colorimeter.

Nitrogen Balance oe Juvenile Southern Quahoc.s

77

SHELLFISH

CULTURE

CONTAINERS

Control

1x104

INFLOW

CELL

DENSITIES

(CELLS/ml.)

5x104

NO
ANIMALS

5x104

(T. ISO)
Indoor Algal Cultures

oo

ooo

Outdoor Algal Cultures
(T. ISO)

6 6
o o

1x105

5x105

□

Nutrients

Figure 1. Experimental design.

Soluble Protein Nitrogen (SPN)

For this method, developed by the authors, the sample
was filtered through a 47-mm Gelman glass fiber filter,
0.45-/i pore size, and the filtrate was retained. Dissolved
protein was precipitated by the addition of 5.0 ml of con-
centrated perchloric acid per 100 ml of sample. The sample
was carefully mixed by swirling and cooled in a circulating
water bath for 2 hours at 5°C. It was then filtered through
double 25-mm Gelman glass fiber filters (0.45-ji pore size).
The sample container, filter holder, and filters were washed
with glass-distilled water. Precipitated protein remaining
on the filters was then determined by the PPN method of
Dorseyet 31.(1077).

The lower limit of sensitivity of the method was deter-
mined by the reagent blank. At least 0.10 /jgat protein
nitrogen must be present on the filters. Thus, a 100-ml
sample with a concentration as low as 1 .0 jugat protein
nitrogen per liter was sufficient for an assay.

This method was linear over the range of 1 .0 to 80 /ugat
protein nitrogen per liter.

Other Nitrogen-Containing Compounds

Standard methodologies were used to analyze nitrate
plus nitrite (Technico Corp. 1978), ammonia (Berg and
Abdullah 1977), urea (DeManche et al. 1973), DFAA

(Coughanower and Curl 1975), and total dissolved nitrogen
(TDN) (D'Elia et al. 1977).

Shellfish Wet Weight, Dry Weight, and Protein Content

Clams were blotted dry with a paper towel and weighed
on a Mettler analytical balance H54AR(precision: ±0.01 mg).
They were then frozen for later analysis. This gave the
whole wet weight value.

When needed for further analyses, the frozen clams were
placed in pretared aluminum weighing dishes and kept at
room temperature for at least 2 hours to ensure that all
clams were gaping. They were then dried in an oven at 70°C
for 24 hours. This gave the whole dry weight value.

No more than 5.0 g whole dry weight of clams were put
into 100 ml of IN NaOH in a 125-ml glass Erlenmeyer flask.
The flask was covered and boiled at 100°C for 100 minutes
along with two flasks containing a standard of Bovine
Serum Albumin and a -IN NaOH blank. The flasks were
swirled and allowed to cool to room temperature.

Duplicate 0.5-ml aliquots were taken from each flask
and placed into acid-washed test tubes that were rinsed in
glass-distilled water.

The supernatant from the flasks was decanted, and the
remaining shells were rinsed repeatedly with glass-distilled
water to remove all traces of NaOH. They were then dried

78

Goldstein and Roels

to constant weight at 70°C for 24 hours in a pretared alum-
inum weighing dish to obtain dry shell weight. Dry meat
weight was taken as the difference between whole dry
weight and dry shell weight.

Tank Deposits

Tank deposits that accumulated over 1 week in each clam
container were collected at the end of the week in a 1-6
polyethylene screw-cap bottle and the volume brought to
1 1 with filtered seawater.

Contents of the bottle were filtered through 47-mm
Gelman glass fiber filters (0.45-^1 pore size). Different
numbers of filters were necessary for different samples
depending on the amount of particulates present. The filters
were stored frozen for later analysis of protein content.
When needed, the filters were put into a pretared aluminum
weighing dish and dried in an oven to constant weight at
70°C for 24 hours.

Filters were digested as described for clams, and protein
content was determined using the method of Dorsey et al.
(1977).

Statistical Tests

Statistical tests used included Edwards' (1972) factorial
analysis of variance (ANOVA) for both independent groups
and repeated measures, Scheffe's test for pairwise differ-
ences, and the one-sample t-test described by Edwards
(1972). A 95% confidence level was the minimum acceptable
level.

RESULTS

Nitrogen Balance

Overall Nitrogen Balance. A nitrogen balance is an
accounting of all nitrogen-containing compounds entering
and leaving a system. In the present study, the concentration
of a number of nitrogenous compounds flowing into and
out of experimental groups of clams was determined.
The total amount of nitrogen "going" to each group of
clams was determined by summing the inflow amounts (in
mg nitrogen) of particulate protein, nitrite ion, nitrate ion,
ammonium ion/ammonia, dissolved free amino acids, urea,
and soluble protein. The total amount of nitrogen "leaving"
each group of clams was determined in a similar manner
except that the protein of the biodeposits (tank deposits)
and the protein gain of the shellfish themselves were added
to this total.

The fraction of total inflow nitrogen (TIN) accounted
for was determined by the calculation:

TIN in =100-(N m -N out )/N in X100.

A summary of those calculations for each of the experi-
mental treatments is shown in Table 2.

TABLE 2.
Nitrogen balance of juveniles of Mercenaria campechiensis.

SN in

2N out

Treatment

(mg/week)

(mg/week)

% Accounted For

1

1761.41

1502.31

85.29

2

485.39

425.06

87.57

3

325.88

298.18

91.49

4

198.28

180.63

91.10

5

166.39

159.59

95.91

Total dissolved nitrogen was determined in all influents
and effluents. That analysis measured all dissolved nitrogen
regardless of its form. Strong oxidizing agents, and high
temperatures and pressures (via autoclaving) oxidized all
N-containing compounds to a nitrite ion which was then
assayed directly.

Thus, a different nitrogen balance can be constructed
using PPN and TDN only. The percent of inflow nitrogen
accounted for when using PPN and TDN only was fairly
constant (see Table 3).

TABLE 3.
Nitrogen balance using PPN and TDN only.

Treatment

Mean Weekly

Nitrogen In

(mg)

Mean Weekly

Nitrogen Out

(mg)

% Accounted For

1

2202.002

1983.078

90.06

2

755.488

680.079

90.02

3

574.676

521.757

90.79

4

430.024

382.847

89.26

5

393.864

351.261

89.18

Particulate protein nitrogen of the outflow included the
PPN of tank deposits (biodeposits) and the gain in protein
by the clams.

Individual Nitrogen-Containing Compounds

Ammonia. The ammonia-N excretion increased with
increasing inflow algal protein concentration (APC). Maxi-
mum excretion of ammonia-N was noted for those clams
receiving an inflow APC of 5.75 /igat PPN/1. Further
increases in inflow APC decreased ammonia excretion
(Table 4).

A t-test (Edwards 1972) was used to determine if the
change in concentration (difference between inflow and
outflow concentrations) of ammonia-N was significant at
the 95% confidence level. Only the change in ammonia-N
concentrations of treatment 3 was significant at the 95%

Nitrogen Balance oe juvenile Southern Quahogs

79

confidence level. That treatment resulted in the fastest
growing animals (see Table 5).

inflow APC of 5.57 /jgat PPN/1. Those clams receiving more
or less APC had lower excretion rates (Figure 2).

TABLE 4.

Percent of total nitrogen accounted for by
individual nitrogen compounds.

Nitrogen Compound

In

PPN
N0 2 ~
N0 3 "
NH 4 +NH 3
DEAA
Urea
SP

PPN
N0 2 ~
N0 3 ~
NH 4 ~ + NH 3
DFAA
Urea
SP

PPN
N0 2 ~
N0 3 "
NH 4 ~ + NH 3
DFAA
Urea
SP

PPN

N0 2 ~

N0 3 "

NH 4 ~ + NH 3

DFAA

Urea

SP

PPN
N0 2 "
N0 3 "
NH 4 " + NH 3
DFAA
Urea
SP

Treatment 1

49.9
1.6

40.1
1.1
1.8
1.7
3.8

Treatment 2

36.6

1.8
46.4

2.4
3.1
5.0

4.7

Treatment 3

27.7
1.9

50.6
3.3
4.1
7.2
5.2

Treatment 4

10.2
2.2

58.8
5.1
5.9

11.5
6.4

Treatment 5

1.6
2.3

62.9
5.9
6.8

13.7
6.9

Out

38.9
1.8

42.2
1.1
2.2
1.4
2.6

30.3
2.0

50.6
4.3
4.0
5.0
3.9

21.1
2.1

51.3
7.6
6.0
7.3
4.6

7.9
3.1
58.3
7.4
8.3
8.6
6.5

1.9

2.5
63.8

6.5
7.7
9.9
7.6

All treatments had the same size, weight, and number of
animals at the start of the experiment. Thus, any difference
in ammonia excretion rates during the first week must be
due primarily to differences in feeding regime. The rate of
excretion of ammonia-N per gram of dry meat weight for
the first week was maximum for those clams receiving an

( ) INFLOW APC
^] OUTFLOW APC

30 35 40 45 50 55 60

ALGAL PROTEIN CONCENTRATION Uigal N/1)

Figure 2. Weight specific ammonia excretion rates as a function of
inflow and outflow algal protein concentration.

Urea. An ANOVA was performed on urea-N concen-
trations of the outflows, and on the dfference between
inflow and outflow concentrations. No significant differ-
ences existed between treatments for either outflows or net
concentrations. Mean weekly inflow concentrations for
each treatment were nearly identical (Table 5).

A t-test showed that changes in urea-N concentrations
were not significant at the 95% confidence level for any
treatment.

Dissolved Free Amino Acid. The DFAA excretion
rate increased with increasing inflow APC until a maximum
"excretion" rate was recorded by those clams receiving an
intermediate inflow APC of 5.75 jugat PPN/1. Further
increases in inflow APC resulted in a decreased excretion
rate (Table 5).

A t-test did not detect a significant difference between
the average weekly mean value of DFAA-N of inflow and
the effluent concentrations. There was no significant
uptake or excretion of DFAA in any of the experimental
treatments at the 95% confidence level.

Soluble Protein. An ANOVA showed a significant
difference (at the 95% confidence level) among treatments
between inflow and effluent soluble protein concentrations.
The net uptake of soluble protein was greatest at the
densest food treatment, and decreased with decreases in
the inflow APC until a net excretion of soluble protein was
noted for those clams receiving only filtered seawater.
However, a t-test showed that the difference between

80

GOLDSTEIN AND ROELS

average weekly inflow and effluent concentrations of soluble
protein for the two lowest food densities was not significant
at the 95% confidence level. There was a net uptake of
soluble protein by those clam populations receiving an
inflow APC greater than or equal to 5.75 tigat PPN/1.

A multiple regression analysis of the difference between
inflow and effluent concentrations of soluble protein on
ingested protein showed a strong (R 2 = 0.87), positive,
nonlinear relationship that was significant at the 95%
confidence level.

TABLE 5.

Mean weekly inflow and effluent concentrations (jugat N/1).

Nitrogen Compound

In

Out

Treatment 1

PPN

56.01

45.40

N0 2

1.77

1.67

N0 3

45.76

41.06

NH 4 +NH 3

1.28

1.05

DFAA

2.05

2.06

Urea

1.88

1.34

SP

4.49

2.62

TDN

85.31

80.73

Treatment 2

PPN

11.33

7.03

N0 2

0.55

0.53

N0 3

14.49

13.81

NH 4 +NH 3

0.76

1.17

DFAA

0.97

1.10

Urea

1.54

1.36

SP

1.51

1.06

TDN

37.15

35.40

Treatment 3

PPN

5.75

2.93

N0 2

0.39

0.39

N0 3 -

10.58

9.84

NH 4 +NH 3

0.69

1.44

DFAA

0.84

1.14

Urea

1.50

1.42

SP

1.14

0.90

TDN

31.14

29.45

Treatment 4

PPN

1.28

0.69

N0 2

0.27

0.36

N0 3

7.45

6.71

NH 4 +NH 3

0.64

0.85

DFAA

0.73

0.95

Urea

1.47

0.98

SP

0.84

0.76

TDN

26.32

23.54

Treatment 5

PPN

0.16

0.16

N0 2

0.24

0.26

N0 3 "

6.67

6.49

NH 4 +NH 3

0.63

0.66

DFAA

0.70

0.78

Urea

1.46

1.01

SP

0.76

0.80

TDN

25.12

22.27

Nitrate. Most of the nitrate flowing to the clams came
from the mass algal cultures as excess nitrate supplied to
the algae. This was shown by the decrease in nitrate concen-
tration of the inflows as the algal cultures were diluted more
and more with filtered seawater to make up the different
food densities. The incoming filtered seawater had a mean
concentration of 6.7 /ugat N0 3 ~— N/1.

An ANOVA indicated significance at the 95% confidence
level among treatments in the difference between nitrate
concentrations of inflow and effluent. However, a Scheffe
test for pairwise differences indicated that only the densest
treatment showed a net change in concentration of N0 3 ~
which was significantly different from the other treatments
at the 95% confidence level. The net uptake of nitrate in
this treatment was probably by living algae in the copious
biodeposits produced by the clams (Table 5).

Nitrite. A pattern of inflow nitrite concentrations
indicated that most of the nitrite came from the algal
cultures. The mean weekly nitrite concentration of the
filtered seawater was 0.24 /Jgat N/1.

An ANOVA indicated a significant difference at the 95%
confidence level among treatments in changes in nitrite
concentration between inflow and effluent. However, a
Scheffe test for pairwise differences indicated that only
the treatment with the greatest inflow APC was significantly
different (at the 95% confidence level) from the other
treatments. The net uptake of nitrite in this treatment was
probably caused by living algae in the biodeposits produced
by the clams (Table 5).

Clam growth, expressed as the mean weekly production
of wet meat, was optimum with the treatments providing an
inflow APC of 1 1 .3 and 5.7 ;ugat protein-N/1 (treatments 2
and 3) (Figure 3).

Q INFLOW APC
□

OUTFLOW APC

DOD

-€

□

ALGAL PROTEIN N CONCENTRATION [ug al N/L )

Figure 3. Growth as a function of inflow and outflow algal protein
nitrogen concentration.

Nitrogen Balance of Juvenile Southern Quahogs

81

Clam growth was significantly higher than that shown
with the higher or lower food densities. It should be
stressed that the food concentration experienced by the
clams was somewhat lower than the inflow concentrations
(7.0 and 2.9 Mgat protein-N/1, respectively) (i.e., effluent
PPN concentrations).

DISCUSSION

An overall determination of the fate of incoming nitrogen
was accomplished by summing the individual concentrations
or amounts of the different compounds. The difference
between total nitrogen of the inflow, and of the effluent
divided by the total nitrogen of the inflow, was the fraction
of total nitrogen not accounted for. In this study, the
percent of inflow nitrogen accounted for varied between
treatments from 85 to 95%.

The missing nitrogen may, in part, be attributed to loss
of free ammonia from the system and from the sample
bottles during analyses. Additionally, only PPN was assayed
in the algal cells and in the clams. The nitrogen present as
nucleic acids, amino sugars, or other forms was not deter-
mined and, thus, was not accounted for. Also, some organic
nitrogen compounds may have been formed as the result of
chemical transformation and not detected in the effluents
from the clams by the analytical techniques used in this
study. Finally, some of the missing nitrogen may be
actually the accumulation of sampling, measurement, and
calculation errors.

Only rarely does a single nitrogen-containing compound,
other than PPN or nitrate, account for more than 10% of
the total nitrogen. Thus, quantitatively. PPN and nitrate
are the most important components of the nitrogen balance,
but some of the other nitrogen-containing compounds have
a qualitative importance. However, in many instances, the
weekly mean change in concentration between inflow and

effluent of a particular compound(s) was not statistically
significant at the 95% confidence level.

The small changes in concentration of nitrogen-containing
compounds between influent and effluent that were noted
in this study may have resulted from attempts to measure
concentrations in a continuous-flow system in which the
volume of seawater flowing past the animals was very great
compared to the biomass of the animals. Thus, very large
amounts of a compound have to be taken up or generated
by the clams to cause a significant change in concentration
between influent and effluent.

Measuring concentration changes of nitrogen-containing
compounds in such a system gives more realistic results
than other types of determinations. Studies in which the
clams were not fed for 24 hours prior to an experiment and
then placed in a bowl of standing synthetic seawater for
24 hours resulted in larger changes in concentration of a
particular compound. However, the results cannot be used
to describe the normal metabolic activity of the animals.
The method described herein approximates more closely
the normal metabolic activity of a feeding clam.

An improvement of this method may result from
increasing the biomass to volume ratio, leading to greater
concentration changes of a nitrogen-containing compound
as it passes through shellfish-culture containers in a
continuous-flow system. That may result in better resolu-
tion of concentration changes associated with static methods
of excretion measurements, but will maintain the realism of
a continuous flow system.

ACKNOWLEDGMENTS

The authors thank Robert Godbout, Lisa McDonald,
Paul McDonald, Diane Spence, and Jacqueline Goldstein for
their fine work, advice, and support.

REFERENCES CITED

Berg, B. R. & M. I. Abdullah. 1977. An automatic method for the

determination of ammonia in seawater. Water Res. 1 1 :637-638.
Coughenower, D. D. & H.C.Curl, Jr. 1975. An automated technique

for total dissolved free amino acids in seawater. Limnol. Oceanogr.

20:128-131.
D'Elia, C. F., P. A. Stendler & N. Corwin. 1977. Determination of

total nitrogen in aqueous samples using persulfate digestion.

Limnol. Oceanogr. 22:760-764.
DeManche, I. M., H. Curl, Jr. & D. D. Coughenower. 1973. An

automated analysis of urea in seawater. Limnol. Oceanogr.

18:686-689.
Dorsey, T. E., P. W. McDonald & O. A. Roels. 1977. A heated

Biuret-Folin protein assay which gives equal absorbance with

different proteins. Anal. Biochem. 78:156-164.
Edwards, A. L. 1972. Experimental Design in Psychological Research.

Holt, Rinehart, and Winston, New York. 220 pp.
Ryther, J. & W. Dunstan. 1971. Nitrogen, phosphorus and eutrophi-

cation in the coastal marine environment. Science 171:1008-1013.
Technicon Corporation. 1978. Technicon Nitrite and Nitrate

Method 43-69W. Tarrytown, New York. 000 pp.

Journal of Shellfish Research, Vol. 1, No. 1, 83-87, 1981.

A STUDY OF TWO SHELLFISH-PATHOGENIC VIBRIO STRAINS ISOLATED FROM A
LONG ISLAND HATCHERY DURING A RECENT OUTBREAK OF DISEASE

CAROLYN BROWN

National Oceanic and A tmospheric Administration,
National Marine Fisheries Service, Northeast Fisheries Center,
Milford Laboratory, Milford, Connecticut 06460

ABSTRACT Two bacterial strains belonging to the genus Vibrio were implicated in a recent outbreak of disease in
larvae of Crassostrea virginica at a Long Island shellfish hatchery. Bacteriological observations made during the disease period
suggested that the two bacterial pathogens represented an extremely small proportion of the total bacterial population in
the seawater system of the hatchery. This was further supported by the appearance of spontaneous disease only after the
tenth day of larval development. Although the two strains were morphologically distinct, their biochemical and physiological
characteristics suggested that they were closely related to Vibrio anguillarum. The disease could be initiated in the labora-
tory when small numbers of the two pathogenic strains were added (2 cells/ml) after each change of larval culture water.
The two strains could be recovered from larval cultures 3 days after a single inoculum of less than 10 cells/ml of larval
culture water, even though the water in the cultures was changed daily. This carry-over of bacterial cells shows that
extremely small numbers of pathogenic cells present in a seawater system can eventually lead to a disease situation. Ultra-
violet radiation was found to be an effective method of eliminating one of the two pathogens. The other partially recovered
from exposure within 24 hours.

INTRODUCTION

In 1956, Walne suggested that too little attention was
being given to the effect of bacteria on shellfish larvae. His
experiments showed that bacterial populations in larval
cultures might be 100 times greater than those in the sea.
Three years later the first laboratory experiments proving
the pathogenicity of specific bacteria were reported by
Guillard (1959). Since that time, many studies have been
conducted to find effective methods of eliminating or, at
least, substantially reducing the occurrence of bacterial
diseases.

The need for routine sanitary procedures has been recog-
nized as good preventative medicine (Tubiash 1975).
Leibovitz (1978) reported that, since individual hatcheries
are different, it is also important to monitor the qualita-
tive physical, chemical, and bacterial changes in larval
culture media to determine optimal conditions for each
hatchery. Certain antibiotics, i.e.. neomycin and chlora-
mphenicol, are recognized as being effective against some
bacteria pathogenic for shellfish (Tubiash et al. 1965, Le
Pennec et al. 1973); their routine use is not recommended,
however, because it can lead to drug resistance. Blogoslawski
et al. (1978) reported that ozone can be an effective disin-
fectant when used with adequate precautions.

A combination of filtration and ultraviolet (UV) light
irradiation of seawater also has been found to reduce
substantially the occurrence of larval diseases (Brown and
Russo 1979). Although these and other disinfection
methods have been reported, shellfish hatcheries generally
do not use them and, therefore, continue to be plagued by
intermittent occurrences of bacterially related diseases
which commonly destroy larval cultures around the sixth
day of development. One such outbreak occurred during
the summer of 1979 at a Long Island (New York) hatchery.

The present paper discusses the findings of an ensuing
investigation.

MATERIALS AND METHODS

Isolation and Identification of Bacteria

During a visit to the hatchery, samples were taken of the
bay water, moribund 10-day-old oyster larvae, and seemingly
healthy 5-day-old oyster larvae. Portions of the samples
were immediately streaked on seawater agar plates consisting
of 0.1% trypticase (BBL)*, 0.1% yeast extract (Difco),
1.0% agar (Difco) in 80% aged, membrane-filtered seawater,
and 20% distilled water. Remaining portions of the samples
were held overnight in screw-capped test tubes at room
temperature and then streaked on seawater agar plates. All
plates were incubated for 2 weeks at 26°C; dominant,
morphologically distinct colonies were selected from plates
inoculated with moribund larvae and grown in seawater
broth (same constituents as agar plates minus the agar).
Broth cultures were incubated at 26°C overnight and
streaked on agar plates for verification of purity. Procedures
described by Evelyn (1971) were used to determine the
physiological and biochemical characteristics of the suspect
pathogens.

Tests for Pathogenicity

The ability of suspect shellfish-pathogenic bacteria to
cause mortality was tested by adding from 10 3 to 10 8
bacterial cells from 24-hour broth cultures of the micro-
organisms to 1 liter of oyster embryonic culture water

"Trade names referred to in this publication do not imply endorse-
ment of commercial products by the National Marine Fisheries
Service.

83

84

Brown

just prior to addition of fertilized oyster eggs, and daily
after each change of culture water. In all cases, including
untreated controls, the fertilized oyster eggs were reared
in 1.3-liter polypropylene beakers at a density of about
15,000 fertilized eggs/liter of lO-jim-filtered, UV-treated
seawater (Brown and Russo 1979). Cultures were main-
tained in a constant-temperature water bath at 26°C. Larval
culture water was changed on a daily basis; larvae were fed
a mixture of laboratory -grown phytoplanktonic cultures of
Isochrysis galbana, Monochrysis lutheri, and Dicrateria
inomata. Larval cultures were sampled and counted on the
second and sixth or seventh day of development using the
procedure described by Brown (1973). Larvae sampled on
the second day were classified into two groups: normal
larvae, those which had developed the standard "D"-shaped
larval shell; and abnormal larvae, those which had shells
that deviated from the standard "D" shape. These two
groups were further subdivided according to whether they
were living or dead prior to fixation. Larvae sampled on the
sixth or seventh day were classified only as alive or dead
prior to fixation, and 50 or 100 live larvae were measured
to the nearest 5 /im. In preliminary experiments to deter-
mine which isolate(s) was pathogenic, culture water was
seeded with an isolate only once, prior to the addition of
fertilized oyster eggs. These embryonic cultures were neither
changed nor fed; on the second day, they were sampled
and discarded. The Student's t test was used to determine
significant differences between controls and experimentals
at P < 0.05. Koch's postulates were satisfied by reisolating
the experimental bacterial strains from moribund larvae
and infecting healthy larvae with the isolates.

Bacterial Control

A modification of procedures described by Brown and
Russo (1979) was used to test the killing efficiency of UV
radiation on the two pathogenic bacterial strains. A black
fiberglass tank having a capacity of 135 liters was filled with
lO-Aim-filtered, UV-irradiated seawater and seeded with a
cell suspension of one of the pathogenic isolates, bringing
the number of pathogenic cells to 10 4 to 10 s /ml of seawater.
Sterile 1.5-liter glass beakers were filled to the 1.0 liter
mark with water taken either directly from the seeded tank
or after UV irradiation, using a flow rate of 3 liters/minute
through an Aquafine Aluminum SL-1 Sterilizer. Samples
were taken from the beakers for total plate counts at
zero time and 24 hours after the beakers had been filled.
Plates were incubated for 1 week at 26°C and counted.

RESULTS AND DISCUSSION

It is not uncommon for a shellfish larval culture to begin
to show overt signs of microbial disease after the tenth day
of development. This is consistent with the possibility that
the responsible microbe(s) is present in the seawater system
at very low numbers but, with time, can reach lethal pro-
portions in larval culture containers. Last summer such an

outbreak of disease occurred at a Long Island hatchery.
Oyster larval cultures routinely were kept for 5 to 6 days
in a small room and then moved to a larger one; within
5 days of the move, they would succumb to disease. The
larvae showed no signs of bacterial swarming at this time.
Globules, however, were found in the umbo of otherwise
healthy looking animals. The nature of these globules is
unknown, but some investigators at the Milford Laboratory
have associated their appearance with disease.

Two bacterial isolates were found capable of producing
mass mortality in laboratory experiments. Preliminary
experiments showed that 3 x 10 8 cells of Strain 1, or
1 x 10 8 cells of Strain 2, added to 1 liter cultures of fertilized
oyster eggs resulted in mass mortality within 24 hours. If
the number of bacterial cells added was reduced to 10 s /liter,
48 hours were required to produce mass mortality.

Examination of the original plates revealed that the two
bacterial isolates grew on plates inoculated with moribund
larvae, and on all plates inoculated with samples that had
been held overnight before culturing: moribund larvae, bay
water, and seemingly healthy larvae. Apparently, the patho-
gens were present in the seawater in very low numbers, but
increased with time to a lethal population size since they
did not grow on plates inoculated at the hatchery.

The two bacterial isolates, although they form colonies
that are morphologically distinct from each other and have
some biochemical differences, may be strains of Vibrio
angiiillarum. Strain 1 forms colonies that are translucent and
have diffusing edges, while Strain 2 forms white, nondiffusing
colonies. Although Strain 1 is morphologically identical to
the Vibrio sp. described by Brown and Losee (1978), some
biochemical and physiological differences do exist between
the two isolates. Table 1 shows common characteristics of the
two isolates from the present study, and the strain reported
by Brown and Losee (1978) with the emerging archetype of
V. anguillarum described by Evelyn (1971). They were
Gram-negative, nonpigmented motile rods capable of
fermenting glucose without gas production. The strains
were oxidase positive and could attack arginine but not
lysine. They were sensitive to Vibriostat. Growth was
inhibited when sodium chloride was either absent or
present in a high concentration (10%). Differences among
the isolates are presented in Table 2. Although vibrios
normally are resistant to penicillin (Shewan 1963), Strain 2
was sensitive to 10 units of penicillin. Strain 2 was able to
produce acid in salicin but not in trehalose. It did not
produce nitrate from nitrite, but it did produce hydrogen
sulfide and deaminate phenylalanine. Unlike the vibrios
described by Evelyn (1971) and by Brown and Losee
(1978), neither Strain 1 nor Strain 2 grew at 5°C. Strain 1
did not produce acid in fructose, mannose, or trehalose.
Whether the differences among the bacterial isolates are
enough to warrant placing them in separate species is not
yet known. The answer must await determination of the
DNA base ratios, moles percent guanine plus cytosine.

Shi lliish-Pathogenic Vibrio

85

TABLE 1.

Common characteristics of three shellfish-pathogenic

vibrios and the emerging archetype of

Vibrio anguillarum *.

TABLE 2.

Characteristic differences between three shellfish-pathogenic
vibrios and Vibrio anguillarum.

Characteristics

Reaction

Characteristics

Reaction

Gram stain

—

Citrate as sole

Pigmented

—

C-source for

Motility

+

growth

+

Fermentative (glucose)

+

Methyl red

Gas from glucose

—

reaction

+

Oxidase (Kovacs)

+

Acetoin

Acid from:

produced

—

Adonitol

—

Gluconate

Dulcitol

—

utilized

—

Inositol

—

Lysine

Inulm

—

decarboxylated

—

Lactose

—

Arginine

Maltose

+

attacked

+

Raffinose

—

Urease

Rhamnose

—

produced

—

Sorbose

—

Ammonium

Sucrose

+

produced

+

Xylose

—

Growth in:

Sensitive to 0/129

+

0% NaCl

—

Catalase produced

+

3% Nacl

+

Starch hydrolyzed

+

7% NaCl

+

Gelatin hydrolyzed

+

10% NaCl

—

■"Characteristics of the emerging archetype of V. anguillarum as
reported by Evelyn (1971).

Table 3 shows that the addition of 10 3 cells of either
one of the two strains, or a combination of the two, will
cause mortality in a liter larval culture within 48 hours.
Live-normal development was significantly less (P < 0.05)
in cultures exposed to Strain 1 (6 x 10 1 cells/ml) or Strain 2
(4 x 10' cells/ml) than in untreated controls. Live-normal
development of fertilized oyster eggs was only 41% in the
presence of Strain 1, and 43% when exposed to Strain 2,
compared to 75% in controls. Exposure to a combination
of the two isolates (5 x 10 1 cells/ml) resulted in 47% live-
normal development. Table 4 shows that survival and growth
were significantly less (P < 0.05) in the presence of Strain 2
than in untreated controls. Survival and size averaged 34%
and 99 jum, respectively, during exposures to Strain 2, while
controls averaged 79% and 116 Mm, respectively. Strain 1
appeared to affect survival (40%) but not growth; mean size
was 115 fim. Only survival was significantly affected (P <
0.05) during exposure to a combination of the two strains.
Data indicate that Strain 2 was more virulent than Strain 1 .
Thirty-three percent fewer cells of Strain 2 were added to
cultures than Strain 1 cells, yet the effect was more severe
in the presence of the former. The fact that a combination
of the two strains did not substantially reduce larval growth
suggests that 4 x 10 1 Strain 2 cells/ml of culture water is
very close to the minimal number of cells required for larval
growth inhibition.

Characteristics

Strain 1
(3)*

Strain 2
(2)

Brown and

Losee(1978)

Vibrio sp.

Evelyn(1971)
V.anguillarum

Sensitive to

penicillin

(10 units)

—

+

—

—

Acid in:

Arabinose

—

—

—

+? Vf

Celtobiose

—

+

+

+

Fructose

—

+

+

+

Galactose

—

—

—

+ V

Glycerol

—

—

+

+

Mannitol

+

+

—

+

Mannose

—

+

+

+

Salicin

—

+

+

—

Sorbitol

—

—

—

+ V

Trehalose

—

—

+

+

Nitrate produced

+

—

+

+

Indole produced

—

+

+

+ V

Hydrogen sulfide

produced

—

+

—

—

Phenylalanine

deaminated

—

+

—

—

Growth at:

5°C

—

—

+

+

37°C

—

—

+

—

*Number within parenthesis indicates number of isolates tested.
fV signifies that 20% or more of the strains compared by Evelyn

(1971) gave reactions different from that indicated for the emerging

archetype.

TABLE 3.

Percentage development of fertilized oyster eggs after
two days of exposure to 10 bacterial cells.

Strain 1 Strain 2 Both

Control

Number of replicates
Live-normal (x ± SE*)
Dead-normal (x ± SE)
Live-abnormal (x ± SE)
Dead-abnormal (x ± SE)
No. bacterial cells
added/ml

12
41 +
30 ±
1 ±

1 ±

12

43 ±

22 +

1 ±

1 ±

6x10* 4x10*

12

47 ± 5t

27 ± 4t

0± Of

1 ± Of

5 x 10 1

12

74 ±11

1 ± 1

1 ±

0+

None

*Standard error at 95% confidence interval.
fSignificantly different (P <0.05).

TABLE 4.

Percentage survival and average size (JJm) of oyster larvae after

six days of exposure to 10 bacterial cells added daily

at each change of culture water.

Strain 1 Strain 2 Both

Control

Number of replicates
Survival (x±SE*)
Size(x±SE)
No bacterial cells
added/ml

10 10 10 10

40 ± 5f 34 ± 7f 35 ± 3t 79+9
115 ± 4 99± 5t 1 10 ± 3 116 +7

6 x 10 1 4x10' 5x10'

None

*Standard error at 95% confidence interval.
fSignificantly different (P <0.05).

86

BROWN

Figure 1 shows that one small inoculum of bacteria could
remain in larval cultures for many days, even when the
cultures were changed daily. Both Strain 1 and Strain 2 were
recoverable from the culture water three days after a single
inoculum of 1 x 10 1 cells/ml and 3 x 10' cells/ml, respec-
tively, was added. The counts increased the first two days,
1 x 10 5 /ml for Strain 2 and 6 x 10 4 /ml for Strain 1, and
then started to decline. This carry over of bacterial cells
illustrates that extremely small numbers of pathogenic cells
present in a seawater system can eventually lead to a
disease situation. The decline may have been due to invasion
into larvae.

48 72

TIME (HR)

Figure 1 . Growth of two pathogenic bacterial strains in oyster larval
cultures over a three-day period.

When the number of bacterial cells was further reduced,
live-normal development was significantly greater in the
presence of Strain 1 (1 cell/ml) than in untreated controls

after two days (Table 5). Development was only 77% in
controls, compared to 84% in exposures to Strain 1 . Although
live-normal development was greater in the presence of
Strain 2 (2 cells/ml) than in controls, the difference was not
considered significant; live-normal development for cultures
exposed to Strain 2 was 81%. Contrary to what was found
in the presence of 10' cells/ml, Table 6 shows that the
addition of very small numbers of two bacterial strains
together had a greater effect than either of the two used
singly. Survival in the presence of Strain 1 (3 cells/ml) was
75%, and 70% in the presence of Strain 2 (1 cell/ml).
Survival and growth of larvae were significantly less (P <
0.05) in cultures exposed to both strains (2 cells/ml) than
in control cultures. Survival averaged 63%, while size was
1 16 jum in the presence of both strains. Survival and growth,
on the other hand, averaged 71% and 121 /im, respectively,
in the controls.

TABLE 5.

Percentage development of fertilized oyster eggs after two days

of exposure to 10 bacterial cells added daily

at each change of culture water.

Strain 1

Strain 2

Control

Number of replicates

10

10

10

Live-normal (x ± SE*)

84 ± 6t

81 ± 6

77 ±6

Dead-normal (x ± SE)

5± 2

4± 2

5±3

Live-abnormal (x ± SE)

2 + 1

3± It

2±1

Dead-abnormal (x ± SE)

2± It

1 ± 1

1 ±1

No. bacterial cells

added/ml

1 x 10°

2x 10°

None

*Standard error at 95% confidence interval,
t Significantly different (P <0.05).

TABLE 6.

Percentage survival and average size (pm) of oyster larvae after

six days of exposure to 10' bacterial cells added daily at

each change of culture water.

Strain 1 Strain 2

Both

Control

Number of replicates

15

15

15

15

Survival (x±SE*)

73 ± 5

70 ± 8

63 ± 8t

71 ±7

Size(x±SE)

120 ± 4

118± 3

116 ± 3t

121 ±4

No. bacterial cells

added/ml

3x 10°

1x10°

2 x 10°

None

*Standard error at 95% confidence interval,
t Significantly different (P <0.05).

Data indicate that at 10 1 cells/ml the two strains, singly
and together, have an adverse effect after only 2 days. If
less than 10 cells/ml are employed, a beneficial effect is
seen at the straight-hinge stage. This effect, however, slowly
declines with time. The decline is probably due to an
increase in bacterial numbers caused by the carry over of
bacteria during changes in the culture water. One possible

Shi lli ish-Pathoginic Vibrio

87

explanation of the data is that the microbes produce a
metabolite which is beneficial in minute quantities, but
becomes detrimental in larger amounts. If this is so, then it
is conceivable that development to the straight-hinge stage
was enhanced during the spontaneous outbreak of this
disease in the commercial hatchery; the number of patho-
genic cells was very small in the bay water.

Table 7 illustrates that the dosage of UV radiation used
in this study was effective in killing cells of Strain 2 but
not of Strain 1. Strain 1 suffered growth inhibition immedi-
ately after the radiation dosage; some cells, however, were
able to recover within 24 hours. It must be kept in mind,
however, that very high numbers of bacteria were used in
this study; whereas, very low numbers were present in the
bay water used by the hatchery. Hence, there is reason to
believe that UV treatment could be effective; Tables 5 and 6
show that at very low numbers both pathogenic strains
were required for the disease process. Killing Strain 2 then
would prevent an outbreak of the disease, at least until
Strain 1 could reach a lethal level. Since it took 10 days
for mortality to occur without treatment, with treatment
the animals should be able to metamorphose before this
level is reached. The animals then would be more resistant
to infection because larval resistance increases with age

TABLE 7.

Effect of ultraviolet (UV) radiation on survival
of two pathogenic Vibrio strains.

Hours

24 Hours

UV*

No UV

UV

NoUV

Strain 1

Strain

4\ 10"
2x]0 4
7x 10 4

5 x 10"
3xl0 4
3 x 10 s

4 \ in 1
3 x 10 2
6 x 10 2

3x 10 5
1 x 10 s
2x 10 s

5 x 10 5
3 x 10 s
9x 10 s

"Numbt'r of pathogenic bacterial cells/ml of seawater.

(Brown 1973). Juvenile clams held at the hatchery were
affected during the outbreak of disease that occurred
during the summer of 1979.

ACKNOWLEDGMENTS

The author thanks Mr. Dave Reylea of the Frank M.
Flower Company, Bayville, New York, for generously
supplying water and oyster larvae samples for this study.

REFERENCES CITED

Blogoslawski, W. J., M. E. Stewart & E. W. Rhodes. 1978. Bacterial

disinfection in shellfish hatchery disease control. Proc. World

Maricult. Soc. 9:589-602.
Brown, C. 1973. The effects of some selected bacteria on embryos

and larvae of the American oyster, Crassostrea virgiiiica. J.

Invertebr. Pathol. 2 1 :2 15 -223.

& E. Losee. 1978. Observations on natural and induced

epizootics of vibriosis in Crassostrea virginica larvae. J. Invertebr.

Pathol. 31:41-47.
Brown, C. & D. J. Russo. 1979. Ultraviolet light disinfection of

shellfish hatchery sea water. I. Elimination of five pathogenic

bacteria. Aquaculture 17:17-23.
Evelyn, T. P. T. 1971. first records of vibriosis in Pacific salmon

cultured in Canada, and taxonomic status of the responsible

bacterium, Vibrio anguillarum. J. Fish. Res. Board Can. 28:

517-525.
Guillard, R. R. L. 1959. further evidence of the destruction of

bivalve larvae by bacteria. Biol. Bull. (Woods Hole)

117:258-266.

Leibovitz, L. 1978. Shellfish diseases. Afar. Fish. Rev. 40:61-64.
Le Pennec, M., D. Prieur & P. Chardi. 1973. Developpement larvaire

de Mytilus edulis (L.) en presence d'antibiotiques. 2 Parties

Action sur la croissance de quatre antibiotiques: aureomycine,

erythromycine, chloramphenicol et sulfamerazine. Rev. Int.

Oce'anogr. Med. 30:115-137.
Shewan, J. M. 1963. The differentiation of certain genera of Gram

negative bacteria frequently encountered in marine environments.

Pages 499-521 in C. H. Oppenheimer (ed.). Symposium on

Marine Microbiology. C. C. Thomas Co., Springfield, Illinois.
Tubiash, H. S. 1975. Bacterial pathogens associated with cultured

bivalve mollusk larvae. Pages 61-71 in W. L. Smith and M. H.

Chanley (eds.). Culture of Marine Invertebrate Animals. Plenum

Press, New York.
, P. E. Chanley & E. Leifson. 1965. Bacillary necrosis, a

disease of larval and juvenile bivalve mollusks. I. Etiology and

epizootiology. J. Bacteriol. 90:1036-1044.
Walne, P. R. 1956. Bacteria in experiments on rearing oyster larvae.

Nature (London) 178:91.

Journal of Shellfish Research, Vol. 1, No. 1, 89-94, 1981.

DIET OF GREEN CRAB CARCINUS MAENAS (L.) FROM
PORT HEBERT, SOUTHWESTERN NOVA SCOTIA

ROBERT W.ELNER

Department of Fisheries and Oceans,

Biological Station

St. Andrews, New Brunswick, Canada, EOG 2X0

ABSTRACT Stomach contents of 762 green crabs Carcinus maenas collected from the intertidal zone at Port Hebert,
southwestern Nova Scotia, during May and August 1978, were examined. Present in the 608 stomachs that contained food
were 20 different, identifiable food items. Bivalves, such as Mya arenaria and Mytilus edulis, were the most important food
items in terms of both estimated volume and frequency of occurrence. Algae, gastropods, and crustaceans appeared of lesser
importance. Cancer crab remains were identified in some stomachs, but there was no evidence of green crab predation on
lobsters. Significant differences were apparent between the green crab diet in May and in August, although the order of
importance of the various food items remained relatively constant. Green crab diet appears to overlap that of sympatric
crab and lobster species. High abundances of 69 and 99 green crabs per-man-hour-searched were found on both sampling
dates, respectively. There were significant differences in crab mean carapace width and male:female sex ratio between the
two samples.

INTRODUCTION

The green crab Carcinus maenas, introduced accidentally
from the eastern Atlantic, is found along the eastern coast
of Canada and the United States from southern Nova Scotia
to Virginia (Holthuis and Gottlieb 1958). Green crab popu-
lation size appears closely associated with long-term temper-
ature trends, reaching maximum abundance during periods
of increasing temperature (Welch 1968). Green crabs were
first observed in Nova Scotia in the early 1950's, in phase
with such a period of increasing temperature (Glude 1955,
MacPhail et al. 1955).

Green crabs are commonly found from the high tide
level down to 3 fathoms (5.5 m) (Crothers 1969), although
some have been reported as deep as 10 fathoms (18.3 m)
(Perkins and Penfound 1971). They occur on all shore types,
but attain maximum abundance in the most sheltered
habitats where they outcompete all other crab species
(Crothers 1970). Adult green crabs migrate up and down
the shore with the tide, but are regularly stranded, under
cover, between tide marks at low tide (Naylor 1958). In
contrast, juveniles appear to remain fairly stationary on
the shore and show no rhythmical migration patterns
(Atkinson and Parsons 1973).

American lobsters Homants americanus can be found
intertidally in southwestern Nova Scotia, and are trapped
commercially in depths as shallow as 3 m (MacKay 1926,
Stasko and Campbell 1980). Sheltered inshore areas are
possibly important 'nurseries' for juvenile lobsters (Mann
1977). Similarly, rock crabs Cancer irroratus, and jonah
crabs Cancer borealis, occur in intertidal and sublittoral
zones. Therefore, since green crabs, Cancer crabs, and
lobsters can coexist in the same habitat in southwestern
Nova Scotia, these species may compete for common
resources.

The only previously published analyses of North Ameri-
can green crab stomachs were performed on specimens from

Massachusetts and New Hampshire (Ropes 1968), and
suggest that prey eaten largely reflects the species available
in the immediate habitat. The present study investigates the
diet of green crabs from the northerly limit of their North
American range to determine how that diet corresponds with
the diet of lobsters and Cancer crabs from the same general
region; and whether small lobsters and Cancer crabs are part
of the diet of green crabs.

METHODS

Male and female green crabs were collected by hand from
a sheltered, rocky bay close to Port Hebert, Queens County,
Nova Scotia, at low tide on the afternoons of May 18 and
August 17, 1978. Collections were timed in terms of crabs
found per-man-hour-searched so that approximate abun-
dance estimates could be made for both dates. All crabs
collected were in a hard-shell condition. They were sexed
and measured across the widest part of the carapace, from
tip to tip of the most distal marginal teeth to enable assess-
ment of size frequency.

Within an hour of capture, the top of each crab's carapace
was pulled away to reveal the stomach sac which was then
removed and preserved in 10% formalin. Contents of each
stomach were identified with the aid of a dissecting micro-
scope. The importance of each food category was evaluated
by a points method, which considers abundance and volume,
and by frequency of occurrence.

The points method (Swynnerton and Worthington 1940)
is especially useful when the food consists of many small
organisms. Points were allotted according to the amount of
food each stomach contained. For example, a full stomach
was allotted 100 points, and a one-third full one was
allotted 33 points. The relative amount of each food category
present was then estimated visually and allocated points,
e.g., the mass of bivalve shells making up three quarters of
the bulk of a half-full stomach (worth 50 points) is worth

89

90

Elner

38 points, while the remaining quarter of the bulk, com-
prised of algae, is then worth 12 points. Although the
personal element influences the visual assessment of the
relative amounts of the different organisms, the method
was felt to indicate adequately the composition of the bulk
of the animals' diet. However, differences in digestion rate
and feeding behavior probably enhance the actual impor-
tance of some food items over others.

Frequency of occurrence of each food category was
recorded on a presence or absence basis. Data from both
points and frequency of occurrence methods were expressed
in percentage terms based on the number of stomachs that
contained food, not on the total number of stomachs
examined. Data from both sexes were combined; Ropes
(1968) and Elner (1977) failed to demonstrate sexual
differences in green crab diet.

RESULTS

Diet of Green Crabs

From the green crab collection in May, 364 stomachs
were analyzed, and from the August collection, 398. From
those crabs collected in May and in August, 71 (20%)
stomachs and 83 (21%) stomachs, respectively, were empty.
Skeletal structures were largely used to identify prey in
the remaining stomachs. Because of the form and fragmented
nature of the remains, assigning a food item to a definite
species was not always possible, but the food usually could
be identified to a more general taxonomic group. Therefore,
the total percentage of stomachs or points for a general
taxonomic group is not necessarily the sum of the percent-
ages from all categories within that group. Figures 1 and 2
show percentage frequencies of occurrence of each major
prey category for the two collection dates. Quantitative
results based on percentage points for each collection date
are given in Figures 3 and 4. Chi-square (X 2 ) tests indicate
significant changes in the relative proportions of the food
categories in the diets of crabs between May and August,
both in terms of frequency of occurrence (X 2 = 72.3; df =
13; P< 0.001) and points (X 2 = 18.27;df= 10;P<0.005).
However, the order of dietary importance of each food
category, in terms of frequency of occurrence and points,
is similar in both samples.

Molluscs appeared to be the most important food items
in terms of frequency of occurrence and points, and were
further separated into four categories. Bivalves, such as
Mytilus eclulis and Mya arenaria, could be recognized by
their shell shape, color, and hinge structure. Although
present, other bivalves, such as Ensis directus and Macoma
baltica, were not plentiful enough to be placed into separate
categories. The gastropods Hydrobia totteni and Littorina
spp. were identified from shell fragments and operculae.
These snails, although encountered frequently, were of low
importance in terms of the points method.

90 r

80

70

60

SO

S. 40

r 30

20

s.^ ,^ J* tr *

*»*

V ■*"

Figure 1. The relative importance of food types (analyzed by
their percentage frequency of occurrence) in the stomachs of
green crabs from Port Hebert, May 1978 (n = 293).

90 r

80-

70

60

50

40

I 30

20

10

^5€^^/^^

o- V

Figure 2. The relative importance of food types (analyzed by
their percentage frequency of occurrence) in the stomachs of
green crabs from Port Hebert, August 1978 (n = 315).

90 r

80

70

60

50

40

30

20

10

0L

Diet or Grken Crabs

90 r

80
70
60

91

-* ^ afc

<^

^jf * *

,r

Figure 3. The relative importance of food types (analyzed by the
percentage points method) in the stomachs of green crabs from
Port Hebert, May 1978 (n = 293).

Crustacea were not common enough to warrant subdivi-
sion into separate food categories. Green crabs and rock
crabs were identified from their chelae, limbs, color, and
exoskeleton. Barnacles, Balamis spp., were identified from
their thick white shells and cirripedia; and amphipods from
their light brown, flattened exoskeletal plates. Other
crustaceans such as Isopoda and hermit crabs (Pagurus spp.)
occurred more rarely. No lobster remains were identified
in the stomachs examined.

Prey items, such as colonial hydroids, bryozoans, various
unidentified eggs, polychaetes (Nereis spp.), and echino-
derms (Strongylocentrotus droebachiensis, Asterias vulgaris ),
were identified infrequently and were placed in a universal
group, 'Others (animals)'. Crescent-shaped pieces of algae
were encountered frequently but in relatively small quanti-
ties, and were separated into brown and green categories
when possible. Material that was unidentifiable by visual
techniques was classed as either 'Unidentified' or 'Uniden-
tified (animals)'. Frequently contained in stomachs examined
were inorganic materials (such as mud or sand particles)
which were classed as 'Sediment'. More exotic nondigest-
ible materials, such as plastic and paint flakes, were also
included in this latter group.

It should be noted that certain epifauna, such as barnacles
or hydroids, could have been ingested accidentally when the
crab ate mollusc or alga prey to which epifauna were attached.

50

40

a- 30

20

10

P "T— — ■

>•» ,y, A K^ \J»

j5» Cv

Or vo

,o~ #-

^ *•>

r^

«y^

f

Figure 4. The relative importance of food types (analyzed by the
percentage points method) in the stomachs of green crabs from
Port Hebert, August 1978 (n = 315).

Size Frequency and Littoral Abundances of Green Crabs

In the May and August surveys, 69 and 99 green crabs,
respectively, were found per-man-hour-searched. Size and
sex composition for samples on both dates are shown in
Figures 5 and 6. The male: female sex ratio changed from
1:0.85 in May to 1:1.26 in August. In the May survey, the
mean carapace width (± standard error) for male green
crabs, 36.4 ±1.2 mm, was significantly larger than that for
females, 28.0 ± 0.9 mm (t = 2.33, df = 362, P < 0.02).
Similarly, there was a significant difference between the
mean carapace widths for male (41 .7 ± 0.9 mm) and female
(36.5 ± 0.7 mm) crabs in the August survey (t = 4.59, df =
396, P < 0.001). Mean carapace width for both male and
female green crabs increased significantly between May and
August (males: t = 3.58, df = 371, P < 0.001; females:
t = 7.28, df= 387. P< 0.001).

DISCUSSION

Stomach analysis strongly suggests that green crabs from
Port Hebert rely on mostly bivalves and, to a lesser extent,
on algae and crustaceans as prey. This trend was confirmed
by both points and frequency of occurrence methods.
Dietary importance of bivalves substantiates the reputation
of green crabs as a major pest of bivalve fisheries (Dare and

92

Elner

Males

May
N = I97, X=36 4+ 1.2 mm

50
40

30
20

10

Females

_May
N= 167, X=28.0± 9mm

10 20 30 40 50 60

Carapace Width (mm)

70

80

Figure 5. Size frequency of male and female green crabs sampled
at Port Hebert, May 1978.

Edwards 1976, Welch 1968). Furthermore, presence of
infaunal bivalves, such as Mya arenaria and Ensis directus in
the stomachs examined, suggests that the green crab is an
efficient burrower.

Significant differences between green crab diets in May
and in August, in terms of points and frequency of occur-
rence, possibly reflected seasonal variations in the abundance
of certain prey.

The only other North American survey on green crab
diet (Ropes 1968) revealed a more diverse diet than the
Port Hebert study but a similar dependence on bivalves.
Elner (1977) analyzed green crab stomach contents from
the Menai Straits, Nortli Wales, and found the diet to consist
mainly of crustaceans and algae. Polychaetes, which were
almost entirely absent from the Port Hebert survey, were
only slightly less important by frequency of occurrence
than molluscs in the North Wales samples. Differences in
diet among the three locations probably reflect the avail-
ability of food types in each particular habitat, and the
crab's opportunistic foraging behavior.

Differences in mean carapace width and sex ratio of the
green crabs sampled between the May and August surveys
could have been caused by seasonal migration as observed

Males

August
N = I76, X= 41.7 td 9mm

50h
40
30
20-

Females

August
N=222, X=36 .5+ 0.7mm

10

20

70

80

30 40 50 60

Carapace Width ( mm)

Figure 6. Size frequency of male and female green crabs sampled
at Port Hebert, August 1978.

by Naylor (1958). Increases in mean carapace width also
may have been due to molting and growth between sampling
dates.

In the laboratory, adult green crabs are able to capture
and feed on juvenile lobsters, and adult lobsters and rock
crabs prey on adult green crabs (R. W. Elner, unpublished
data). Although no lobster remains were identified in the
stomachs examined, there was evidence of cannibalism and
predation on Cancer irroratus. Klein-Breteler (1975)
suggests that predation by larger green crabs on smaller
ones is an effective density-dependent mortality factor.
Laboratory observations (R. W. Elner, unpublished data)
have shown that all sizes of green crabs are vulnerable to
cannibalism after ecdysis.

In surveys of lobster diets from Newfoundland (Ennis
1973, Squires 1970), and from the Northumberland Strait
(Miller et al. 1971), bivalves, gastropods, crabs, polychaetes,
and echinoderms were the most frequently occurring food
items. However, each survey produced different proportions
and positions of importance for each food category. This
variability is probably explained by the different habitats,
and subsequent differences in prey availability in which the
sampling took place. Scarratt and Lowe (1972) determined

Diet or Green Crabs

93

the diet of the rock crab in the Northumberland Strait to
be composed principally of polychaetes, mussels, and sea
urchins. In a study off Shelburne, southwestern Nova Scotia
(R. W. Elner, unpublished data), crabs, bivalves, and brittle
stars were the major food items in lobster stomachs based
on the points method; bivalves, crabs, and amphipods were
dominant in rock crab stomachs. There are no published
data on jonah crab diet, although it can be expected to be
similar to that of the rock crab. The many similarities in
diet among green crabs, rock crabs, and lobsters indicate
that in food-limiting situations these species probably com-
pete for food types such as bivalves, gastropods, polychaetes,
and crustaceans. Elner and Hughes (1978), Elner and Jamie-
son (1979), and Elner and Raffaelli (1980) have shown that
green crabs, rock crabs, and lobsters are versatile molluscan
predators able to open the shells of a wide size range of
prey; therefore, competition is unlikely to be lessened sub-
stantially by any partitioning of food resources on the basis
of prey size.

Miller et al. (1971) determined that American lobsters
endure intense interspecific competition for food within
kelp communities. Scarratt (1968) for American lobsters.

and Chittleborough (1970, 1975) and Chittleborough and
Phillips (1975) for western rock lobsters (Panulints longipes),
found evidence of intense spatial competition on lobster
grounds. Competitive interactions can depress the carrying
capacity of a habitat for the species concerned, and displace
members into marginal habitats where they may be inade-
quately nourished and subject to increased predation. High
abundances of green crabs, as observed in these surveys,
may be capable of sufficiently depressing the carrying
capacity of an inshore habitat, in terms of space and food,
resulting in a decreased abundance of lobsters and Cancer
crabs. Therefore, the green crab should be viewed not only
as a proven direct pest of commercial molluscs but also as
a possible indirect and direct competitor of lobsters and
other crab species.

ACKNOWLEDGMENTS

I am indebted to Jim Steeves and Dr. Janet K. Elner who
helped collect and process the green crabs. I also thank Drs.
Alan Campbell, Peter Daye, and Aivars Stasko for critically
reviewing drafts of the manuscript. Figures were prepared
by Frank Cunningham.

REFERENCES CITED

Atkinson, R. J. A. & A. J. Parsons. 1973. Seasonal patterns of
migration and locomotor rhythmicity in populations of Carcinus.
Neth.J. Sea Res. 7:81-93.

Chittleborough, R. G. 1970. Studies on recruitment in the western
Australian rock lobster, Panulints longipes cygnus George:
density and natural mortality of juveniles. Aust. J. Mar. Fresh-
water Res. 21:131-148.

. 1975. Environmental factors affecting growth and survival

of juvenile rock lobsters Panulirus longipes (Milne-Edwards).
Aust. J. Mar. Freshwater Res. 26 : 1 77 - 196.

& B. F. Phillips. 1975. Fluctuations of year-class strength

and recruitment in the western rock lobster Panulirus longipes
(Milne-Edwards). Aust. J. Mar. Freshwater Res. 26:31 7-328.

Crothers, J. H. 1969. The distribution of crabs in Dale Roads
(Milford Haven: Pembrokeshire) during summer. Fid. Stud.
3:109-124.

. 1970. The distribution of crabs on rocky shores around

the Dale Peninsula. Fid. Stud. 3:263-274.

Dare, P. J. & D. B. Edwards. 1976. Experiments on the survival,
growth and yield of relaid seed mussels (Mytilus edulis L.) in
the Menai Straits, North Wales. /. Cons. Int. Explor. Mer 37:
16-28.

Elner. R. W. 1977. The predatory behaviour of Carcinus maenas
(L.). Ph.D. thesis. University College of North Wales, Bangor.
91 pp.

& R. N. Hughes. 1978. Energy maximization in the diet of

the shore crab, Carcinus maenas. J. Anim. Ecol. 47:103-1 16.

Elner, R. W. & G. S. Jamieson. 1979. Predation of sea scallops,
Placopecten magellanicus. by the rock crab, Cancer irroratus.
and the American lobster, Homarus americanus. J. Fish. Res.
Board Can. 36:537-543.

Elner, R. W. & D. G. Raffaelli. 1980. Interactions between two
marine snails, Littorina rudis Maton and Littorina nigrolineata
Gray, a predator, Carcinus maenas (L.), and a parasite. Micro-
phallus similis Jiigerskiold. J. exp. mar. Biol. Ecol. 43:151-160.

Ennis, G. P. 1973. Food, feeding and condition of lobsters, Homarus

americanus. through the seasonal cycle in Bonavista Bay, New-
foundland./. Fish. Res. Board Can. 30:1905-1909.
Glude, J. B. 1955. The effects of temperature and predators on

the abundance of the soft-shell clam, My a arenaria, in New

England. Trans. Am. Fish. Soc. 84:13-26.
Holthuis, L.B.& E.Gottlieb. 1958. An annotated list of the decapod

Crustacea of the Mediterranean coast of Israel, with an appendix

listing the Decapoda of the eastern Mediterranean. Bull Res.

Counc. Israel 18:1-126.
Klein-Breteler, W. C. M. 1975. Laboratory experiments on the

influence of environmental factors on the frequency of moulting

and the increase in size at moulting of juvenile shore crabs.

Carcinus maenas. Neth. J. Sea Res. 9:100-120.
MacKay, D. A. 1926. Report on lobster investigations at St. Mary

Bay, Digby County, N.S., 1926. Biol. Board Can. MS Rep.

Biol. Sta. 1:1-6.
MacPhail, J. S., E. I. Lord & L. M. Dickie. 1955. The green crab-a

new clam enemy. Fish. Res. Board Can., Progr. Rep. Atl. Coast

Sta. 63:3-11.
Mann , K. H. 1 9 7 7 . Destruction of kelp beds by sea urchins; a cyclical

phenomenon or irreversible degradation. Helgolander wiss.

Meeresunters. 30:455-467.
Miller. R. J., K. H. Mann & D. J. Scarratt. 1971. Production potential

of a seaweed-lobster community in eastern Canada. /. Fish. Res.

Board Can. 28:1733-1738.
Naylor, E. 1958. Tidal and diurnal rhythms of locomotory activity

in Carcinus maenas (L.). J. Exp. Biol. 35:602-610.
Perkins, E. J. & J. M. Penfound. 1971. Carcinus-tbe abundant

enigma. Spectrum, Brit. Sci. News 84:7-8.
Ropes, J. W. 1968. The feeding habits of the green crab, Carcinus

maenas (L.). Fish. Bull. 67:183-203.
Scarratt. D. J. 1968. An artificial reef for lobsters (Homarus ameri-
canus). J. Fish. Res. Board Can. 25 :2683-2690.

& R. Lowe. 1972. Biology of rock crab (Cancer irroratus)

in Northumberland Strait./ Fish. Res. Board Can. 29:161-166.
Squires, H. J. 1970. Lobster (Homarus americanus) Fishery and

94 ELNER

ecology in Port-au-Port Bay, Newfoundland, 1960-65. Proc. Aquat. Sci. 954:208-224.

Nat. Shellfish. Assoc. 60:22-39. Swynnerton, G. H. & E. B. Worthington. 1940. Note on the food

Stasko, A. B. & A. Campbell. 1980. An overview of lobster life of fish inHaweswater (Westmorland). J. Anim. Ecol. 9:183-187.

history and fishery in southwestern Nova Scotia. Proceedings Welch, W. R. 1968. Changes in abundance of the green crab, Carcinus

of the workshop on the relationship between sea urchin grazing maenas (L.), in relation to recent temperature changes. Fish.

and commercial plant/animal harvesting. Can. Tech. Rep. Fish. Bull. 67:337-345.

Journal of Shellfish Research, Vol. 1, No. 1, 95-99, 1981.

VARIATIONS IN SOME REPRODUCTIVE ASPECTS OF
FEMALE SNOW CRABS CHIONOECETES OPILIO 12

STEPHEN C. JEWETT

Institute of Marine Science, University of Alaska,
Fairbanks, Alaska 99701

ABSTRACT Knowledge of the reproductive biology of female snow crabs (Chionoecetes opilio) from northern Alaska
waters is important because of the potential impact on this dominant species from increased petroleum-related activities
there. Size at 50% maturity for female snow crabs from the southeastern Chukchi Sea is 50 mm carapace width. Fecundity
of three North American populations of Chionoecetes opilio decreases progressively at a given body size with increasing
latitudes. Crabs from the southeastern Chukchi Sea have a smaller body-size range and larger eggs than those from the
southeastern Bering Sea and from the Gulf of St. Lawrence. Also, a small percentage (3.3%) of female Chukchi Sea crabs
of egg-bearing size are ovigerous.

INTRODUCTION

Snow (tanner) crabs Chionoecetes opilio (O. Fabricius)
are present on both sides of the North Pacific Ocean— to the
west in the Sea of Japan, and to the east in the Bering
Sea— where they extend northward to Chukchi Sea and
Arctic Ocean (Wolotira et al. 1977; Yoshida 1941 ; K. Frost,
Alaska Department of Fish and Game, personal communi-
cation). In the Atlantic Ocean, they range from the Gulf of
Maine northward through the Gulf of St. Lawrence (Garth
1958).

Various reproductive aspects (i.e., maturity, mating, egg
deposition, fecundity, and egg size) of female C. opilio have
been reported from many geographic localities (Brunei
1960, 1961, 1962; Ito 1963, 1967; Powles 1968; Watson
1969, 1970; and Haynes et al. 1976). This paper compares
some reproductive aspects of C. opilio toward the northern
limit of its range, the southeastern Chukchi iSea (68° 1 8. 0'N),
with data from the southeastern Bering Sea (56°15.0'N),
from the Gulf of St. Lawrence (48°43.5'N and 48°21.0'N)
(Haynes et al. 1976), and, to a limited extent, from the Sea
of Japan (approximately 35° 50.0'N) (Ito 1963).

Additionally, baseline knowledge of various reproductive
aspects of female snow crabs from northern Alaska waters
is important because of the potential increase in petroleum-
related activities in that area. Baseline data can be compared
with data from future impacts, if any, on this dominant
crab species.

METHODS

In the Chukchi Sea near Point Hope, Alaska, 193 new-
shell females (130 immature and 63 mature individuals)

This study was supported under contract No. 03-5-022-56
between Dr. Howard M. Feder, University of Alaska, and NOAA,
Department of Commerce, through the Outer Continental Shelf
Environmental Assessment Program to which funds were provided
by the Bureau of Land Management, Department of Interior.
Contribution No. 437, Institute of Marine Science, University of
Alaska, Fairbanks. Alaska 99701.

were collected during a northeastern Bering Sea-southeastern
Chukchi Sea benthic trawl survey in September— October
1976 (Wolotira et al. 1977, Feder and Jewett 1978). Speci-
mens were selected to encompass the size range of ovigerous
individuals and to determine size at maturity.

Carapace width, the widest portion of the carapace
excluding spines, was measured to the nearest 0.1 mm.

Eggs were dried to a constant weight at 60°C (see
Lovegrove [1966] for drying technique) and weighed to
the nearest 0.001 g.

After drying, the eggs were rubbed gently to free them
from connective tissue. Two estimates of egg number were
obtained for each crab by comparing the weight of a 200-egg
subsample to the weight of the entire egg mass (Lagler
1957). The mean of the two estimates was used in all
calculations.

The number of eggs from crabs of the same size have been
reported to decrease approximately 50% from the time of
egg extrusion to the time of hatching (Brunei 1962, Kon
1976); presumably this egg loss was due topredation,unfer-
tilization, and/or abnormalities. Therefore, to make adequate
latitudinal comparisons in snow crab fecundity, crabs with
eggs in the early stages of development were collected for
comparison with eggs of similar stages of development from
the southeastern Bering Sea and from the Gulf of St. Law-
rence. Fecundity may be a function of spawning history,
i.e., differences in clutch size may exist between primiparous
and multiparous spawners. This aspect was not examined.

To determine egg diameter, a sample of 10 eggs from
each of five crabs was removed from the blotted egg mass,
and the diameter measured to 0.01 mm with an ocular
micrometer.

RESULTS AND DISCUSSION

The geometric mean (GM) regression (Ricker 1973) was
used as the measure to express the functional regression of
number of eggs (Y) on carapace width (X). The GM regres-
sion method also was used by Haynes et al. (1976) for
C. opilio fecundity data from the southeastern Bering Sea

95

96

JEWETT

and from the Gulf of St. Lawrence. It is presented here for
comparison. The relationship between log fecundity and
log carapace width is expressed as:

log e Y = log e M+t'log e X.

The correlation coefficient for Chukchi Sea crabs was
0.767, indicating a reasonably good relationship between
number of eggs and carapace width (Table 1). Similar
correlation coefficients were obtained for crabs from the
southeastern Bering Sea and from the Gulf of St. Lawrence,
i.e., 0.808 and 0.733, respectively.

Ninety-five percent confidence intervals of the regression
coefficients (v) were used to test the null hypothesis that
the slope equaled 3 for C. opilio in the Chukchi Sea; a
similar test was made on crabs from the southeastern Bering
Sea and from the Gulf of St. Lawrence (Haynes et al. 1976).
Regression coefficients for crabs from the Chukchi Sea,
as well as those from the southeastern Bering Sea, were not
significantly greater than 3, indicating that egg number and
carapace width increased at similar rates. The number of
eggs of C. opilio from the Gulf of St. Lawrence increased
at a rate greater than the width of the crab (Haynes et al.
1976).

TABLE 1.

Relationship of log number of eggs to log carapace width
for Chionoecetes opilio from three geographic localities.

Parameters

Southeastern Southeastern Gulf of St.
Chukchi Sea Bering Sea Lawrence

Latitude 68 18.0

Number of crabs 63

Regression coefficient

V 3.4822

95% confidence limits ± 0.5720

Intercept log g Ql) - 3.6905

Correlation coefficient (V) 0.7670

56 15.0

23

48"43.5
48°21.0'
99

2.7206 4.2000

± 0.7265 ± 0.5686

- 0.7125 - 6.7472

0.8086 0.7329

Source: Haynes et al. 1976.

Size at Maturity

The smallest mature and largest immature female crabs
were 40.3 mm and 54.0 mm, respectively, indicating an
approximate 14 mm size difference between the smallest
and largest immature female ready to molt to maturity.
Size at 50% maturity was the same as that for females from
the Gulf of St. Lawrence (Watson 1970), i.e., about 50 mm.
Female C. opilio elongatus from Korean waters mature at
63 mm (Yoshida 1941), whereas 50 to 55 mm was the size
at maturity of the same species from the Sea of Japan
(Kato et al. 1956, Ito 1967). Female C. bairdi from the
Gulf of Alaska reached 50% maturity at approximately
80 mm (Hilsinger 1976).

Carapace Width- Fecundity

Observed mean number of eggs for a given carapace
width group (5 mm) was smaller for C. opilio from the
Chukchi Sea than for C. opilio from the southeastern Bering
Sea and Gulf of St. Lawrence (Table 2; Figure 1). The
smallest ovigerous female size class from Chukchi Sea was
approximately 10 mm smaller than the smallest ovigerous
female size class from the southeastern Bering Sea and the
Gulf of St. Lawrence. The largest Chukchi Sea female size
class was approximately 15 mm smaller than the largest
Bering Sea crab size class and nearly 25 mm smaller than
the largest Gulf of St. Lawrence crab size class (Table 2).
Maximum difference between the lowest and highest
number of eggs in a 5-mm size group in Chukchi Sea crabs
was 24,773 eggs (50 to 54 mm); the mean difference was
10,647 eggs. Maximum and mean differences in the south-
eastern Bering Sea crabs were 30,452 eggs (55 to 59 mm)
and 17,857 eggs, respectively; in the Gulf of St. Lawrence
the differences were 64,787 eggs (70 to 74 mm) and 52,088
eggs, respectively.

TABLE 2.

Observed mean fecundity (x 10 eggs) of Chionoecetes opilio
(number of crabs in parentheses) from three localities.

Carapace
width (mm)

Gulf of
St. Lawrence

Southeastern

Bering Sea

Southeastern
Chukchi Sea

40-44
45-49
50-54
55-59
60-64
65-69
70-74
75-79
80-84
85-89

31.8 (1)

28.2 (2)

39.6 (8)

33.3(5)

44.1 (21)

37.4(5)

65.5(28)

44.6 (5)

70.9(23)

49.8 (5)

97.9(12)

74.8(1)

117.5 (3)

114.9 (3)

12.9 (8)
19.2(19)
25.5 (22)
28.0(11)
37.1 (3)

'Source: Evan Haynes, National Marine Fisheries Service, Auke
Bay, Alaska.

Ito (1963) examined the fecundity of C. opilio from the
southeastern part of the Sea of Japan and determined that
most crabs carried 30,000 to 80,000 eggs per individual
(range = 5,500 to 150,000); the mode was approximately
50,000 to 60,000 eggs. Corresponding crab sizes were not
presented.

Egg Size

The range (0.64 to 0.88 mm) and mean size (0.71 mm)
of eggs from Chukchi Sea crabs were greater than those for
eggs from the southeastern Bering Sea (range: 0.56 to
0.74 mm; mean: 0.66 mm), and from the Gulf of St.
Lawrence (range: 0.56 to 0.75 mm; mean: 0.65 mm).
Coefficients of variation of egg size among Chukclii Sea
crabs ranged from 2.4 to 5.5%, indicating uniform egg size.

Some Reproductive Aspects oi- Chjonoecetes opilio

97

—

E

5,

3
O.

E
o

ON

(spuesnoqj) SD03

o

0)

<

ca

Q-

«

o

<

2 u

(0

tz

3 5

<

o Si

o

2 «

•5 -J
c „ •

^£

0) —

IT)

ir>

=5 3

o O

■-■ Z.

■2 c
>: «

tfl CO

£ 1

a a

o

o c

in

P= 5

O 3
vl o

g§ ".

» M
— 0)
CO

m

S r

**

■2 u

<*—

o E

I -

E x)

o

*t

• o
h- —

3j ■o

98

JEWETT

Similar uniformity in egg size of crabs existed for crabs
from the southeastern Bering Sea and the Gulf of St.
Lawrence. No significant correlation was found between
mean egg size and crab size for crabs of the Chukchi Sea
region (r = —0.530); this lack of relation between sizes of
crab and egg was consistent with data from the other two
areas.

Gravid Females

Changes in percentages of egg-bearing females may
indicate that stocks were over-exploited or under environ-
mental stress (Hilsinger 1976). Only a small proportion of
female Chionoecetes opilio of the northeastern Bering Sea
and the southeastern Chukchi Sea were gravid. Among
5,200 females exceeding 40 mm in carapace width (size of
the smallest ovigerous female), only 169 (3.3%) were bearing
eggs (Wolotira et al. 1977). Additionally, examination of

the ovaries of 130 immature and 63 mature females revealed
that 48 and 97%, respectively, had developing internal
orange ova (Table 3). This high proportion of females with
advanced ovarian development and low proportion of
egg-bearing females seems paradoxical. The seminal recep-
tacles of mature females were not examined to determine
the presence or absence of sperm. Snow crabs are not
commercially exploited in the northeastern Bering Sea or in
the southeastern Chukchi Sea; therefore, the reduction of
egg-bearing females may be environmentally related, but no
information is available to substantiate this.

ACKNOWLEDGMENTS

Special thanks go to Mr. Evan Haynes for his assistance
and critical review of this manuscript, and to Mr. Robert
Sutherland for his statistical assistance.

TABLE 3.

Maturity of 130 immature and 63 mature Chionoecetes opilio from southeastern Chukchi Sea.

Carapace Width (mm)

Totals

Maturity

15-

19

20-24

25-29

30-34

35-39

40-44

45-49

50-54

55-69

60-64

Percent

Number of Crabs

Immature

ovary absent

ovary present, empty and white

ovary orange

8
7

3
4

3
5

3

12

1

3
3

1

3

12

3

1

34

1

23

23
45
62

130

18

34
48

100

Mature

ovary orange

ovary empty and white

8

18

1

22

10

1

3

61

2

63

97
3

100

'Source: Hilsinger (1976).

REFERENCES CITED

Brunei, P. 1960. Observations sur la biologic et biometrie du crabe-
araignee Chionoecetes opilio (Fabr.). Rapp. Stn. Biol. mar.
Grande-Riviere. P.Q.:59-67. (Translated from French by Linda
Nielson, National Marine Fisheries Service, Alike Bay, Alaska.)

. 1961. Nouvelles observations sur la biologie et la bio-
metrie du crabe-araignee Chionoecetes opilio (Fabr.). Rapp.
Stn. Biol. mar. Grande-Riviere. P.Q.:63-71. (Translated from
French by Linda Nielson, National Marine Fisheries Service,
Auke Bay, Alaska.)

. 1962. Troisieme serie de'observations sur la biologie et

la biometride du crabe-araignee Chionoecetes opilio (Fabr.).
Rapp. Stn. Biol. mar. Grande -Riviere. P.Q.:81-89. (Translated
from French by Linda Nielson, National Marine fisheries Service.
Auke Bay, Alaska.)
Feder, H. M. & S. C. lewett. 1978. Survey of the epifaunal inverte-
brates of Norton Sound, southeastern Chukchi Sea, and Kotzebue
Sound. Institute of Marine Science Report R78- 1. University of
Alaska, Fairbanks. 124 pp.

Garth, J. S. 1958. Brachyura of the Pacific coast of America.
Oxyrhyncha. Allan Hancock Pacific Exped. 21(1 & 2). 854 pp.

Haynes, E., J. R. Karinen, J. Watson & D. J. Hopson. 1976. Relation
of number of eggs and egg length to carapace width in the
brachyuran crabs Chionoecetes bairdi and C. opilio from the
southeastern Bering Sea and C. opilio from the Gulf of St.
Lawrence. J. Fish. Res. Board Can. 33:2592-2595.

Hilsinger, .1. R. 1976. Aspects of the reproductive biology of female
snow crabs, Chionoecetes bairdi, from Prince William Sound and
adjacent Gulf of Alaska. Mar. Sci. Comm. 2(3 &4):201-225.
Ito, K. 1963. A few studies on the ripeness of eggs of zuwai-gani
Chionoecetes opilio. Bull. Jpn. Sea Reg. Fish. Res. Lab. 11:65-76.
(Translated from Japanese by Fisheries Research Board of
Canada Translation Service No. 1117.)

. 1967. Ecological studies on the edible crab, Chionoecetes
opilio (O. Fabricius), in the Japan Sea. I. When do female crabs
first spawn and how do they advance into the following repro-
ductive stage. Bull. Jpn. Sea Reg. Fish. Res. Lab. 17:67-84.

Some Reproductive Aspects oe Chionoecetes opilio

99

(Translated from Japanese by Fisheries Research Board of

Canada Translation Service No. 1 103.)
Kato, G., I. Yamanaka, A. Ochi & T. Ogata. 1956. General aspects

on trawl fisheries in the Japan Sea. Bull. Jpn. Sea Reg. Fish. Lab.

4:1-331. (In Japanese with English summary; translation of

pp. 293—305 , available from National Marine Fisheries Service,

Seattle, WA.)
Kon, T. 1974. Fisheries biology of the Japanese tanner crab. VI. On

the number of ovarian eggs and eggs held on the pleopods. Bull.

Jpn. Soc. Sci. Fish. 40(5):465-469.
Lagler, K. F. 1956. Freshwater Fishery Biology. 2nd edition. Wm. C.

Brown Co., Dubuque, Iowa. 421 pp.
Lovegrove,T. 1966. The determination of the dry weight of plankton

and the effects of various factors in the values obtained. Pages

429-467 in Harold Barnes (ed.), Some Contemporary Studies in

Marine Science. George Allen and Unwen Ltd., London. 716 pp.
Powles, H. W. 1968. Observations on the distribution and biology

of the spider crab, Chionoecetes opilio. Fish. Res. Board Can.
MS Report Series (Biol.) No. 950. 30 pp.

Ricker, W. E. 1973. Linear regression in fishery research. J. Fish.
Res. Board Can. 30:409-434.

Watson, J. 1969. Biological investigations on the spider crab, Chionoe-
cetes opilio. Can. Fish. Rep. 13:24-27.

. 1970. Maturity, mating, and egg laying in the spider crab,

Chionoecestes opilio. J. Fish. Res. Board Can. 27(9): 1607-1616.

Wolotira, R. J., Jr., T. M. Sample & M. Morin, Jr. 1977. Demersal
fish and shellfish resources of Norton Sound, the southeastern
Chukchi Sea, and adjacent waters in the baseline year 1976.
U.S. Dep. Comm., NOAA, NME'S, Northwest and Alaska Fisheries
Center, Washington. Processed Report. 292 pp.

Yoshida, H. 1941. On the reproduction of useful crabs in North
Korea (II). Suisan Kenkyushi 36:116-121. (Translation from
Japanese, available from National Marine Fisheries Service,
Seattle, Washington.)

Journal of Shellfish Research, Vol. 1, No. 1, 101-126. 1981.

ABSTRACTS OF TECHNICAL PAPERS

Presented at 1980 Annual Meeting

NATIONAL SHELLFISHERIES ASSOCIATION

Hyannis, Massachusetts
June 9-12, 1980

National Shellfisheries Association, Hyannis, Massachusetts Abstracts, 1980 Annual Meeting, June 9-12, 1980 103

CONTENTS

Betsy Brown, Leslie Williams and Melbourne R. Carriker

Role of Chemoreception in Predation by the Oyster Drill Urosalpinx cinerea. I. Feeding Behavior 107

George R. Abbe

Nonradiological Studies of Tray-Held Oysters, Crassostrea virginica, in the Vicinity of

the Calvert Cliffs Nuclear Power Plant in Chesapeake Bay, 1970-1979 107

T. Amaratunga

The Short-Finned Squid lllex illecebrosus Fishery in Eastern Canada 107

T. Amaratunga

A Study of the Growth and Feeding Parameters of the Short-Finned Squid lllex

illecebrosus in Relation to a Fishery Model 108

Richard S. Appeldoorn, Robert S. Brown and Keith R. Cooper

Factors Affecting the Development of Molluscan Neoplasia in the Soft-Shell Clam

Mya arenaria: Indications from Laboratory and Field Observations 108

Walter J. Blogoslawski, Stephen T. Tettelbach, Lisa M. Petti and Barry A. Nawoichik

Isolation, Characterization, and Control of a Vibrio sp. Pathogenic to Crassostrea

virginica and Ostrea edulis Larvae 1 09

V. M. Bricelj and R. E. Malouf

Aspects of Reproduction of Hard Clams, Mercenaria mercenaria, in Great South Bay, New York 109

James T. Carlton and Roger Mann

Population Maintenance, Manageability, and Utilization of Introduced Species: Path-
ways, Patterns, and Case Histories 109

Melbourne R. Carriker, Robert E. Palmer and Robert S. Prezant

New Information on the Functional Ultrastructure of the Valves of the Oyster Crassostrea virginica 110

L. R. Connell, Jr. and R. E. Loveland

Growth Rates and Fouling in Sediment-Free Raft Culturing of Juvenile Hard Clams,

Mercenaria mercenaria (L.) 110

Keith R. Cooper and Robert S. Brown

Diagnosis and Prognosis of an Hematopoietic Neoplasm in the Soft -Shell Clam Mya arenaria L Ill

Robert K. Cox

The Geoduck Clam Fishery in British Columbia, Canada Ill

E. G. Dawe

Development of the Newfoundland lllex illecebrosus Fishery and Management of the Resource Ill

E. G. Dawe

Forecasting Inshore Abundance of Squid lllex illecebrosus from a Preseason Biomass Survey 112

E. G. Dawe

Progress Toward Validating the Aging of Short-Finned Squid Using Statoliths 112

N. Dean Dey

Growth of Sibling Hard Clams, Mercenaria mercenaria, in a Controlled Environment 112

R. Elston, L. Leibovitz, D. Relyea and J. Zatila

Diagnosis of Vibriosis in a Commercial Oyster Hatchery Epizootic, A Case History 113

Arnold G. Eversole, Peter J. Eldridge and William K. Michener

Reproductive Response to Increased Density: Some Observations from Molluscs 113

Lowell W. Fritz and Dexter S. Haven

An Investigation of Sea Scallops (Placeopecten magellanicus) of the Mid-Atlantic from

Commercial Samples in 1979 114

Scott M. Gallager and Roger Mann

An Apparatus for the Measurement of Grazing Activity of Filter Feeders at Constant

Food Concentrations 114

R. B. Gillmor

Intertidal Growth in Mytilus edulis L 114

Julius Gordon, Daniel Rittsehof, Leslie Williams and Melbourne R. Carriker

Preliminary Chemical Characterization of Mantle Cavity Fluid of the Oyster Crassostrea virginica 115

104 Abstracts, 1980 Annual Meeting, June 9-12, 1980 National Shellfisheries Association, Hyannis. Massachusetts

CONTENTS (Continued)

Herbert Hidu

Mya arenaria— Nonobligate Infauna 116

Roy W. M. Hirtle and Ronald K. O'Dor

A Comparison of Feeding and Growth in Natural and Captive Squid (Illex illecebrosus) 116

R. F. Hixon, R. T. Han Ion and W. H. Hulet

Growth, Fecundity and Estimated Life Span of Three Loliginid Squid Species in the

Northwestern Gulf of Mexico 116

R. M. Ingle, D. G. Meyer and M. R. Landrum

Preliminary Notes on a Pilot Plant for the Feeding of Adult American Oysters 116

Douglas S. Jones

Reproductive Cycles of the Ocean Quahog Arctica islandica and the Atlantic Surf

Clam Spisula solidissima off New Jersey 117

Richard C. Karney

Shellfish Propagation on Martha's Vineyard 117

Victor S. Kennedy and William C. Boicourt

Water Circulation and Oyster Spat Settlement in Two Adjacent Tributaries of the

Choptank River, Maryland 118

A. M. T. Lange

History and Present Conditions of Squid, Loligo pealei and Illex illecebrosus. Fisheries

off the Northeastern Coast of the United States 118

A.M. T. Lange

Yield-per-Recruit Analysis for Squid, Loligo pealei and Illex illecebrosus, from the Northwest Atlantic 118

Roger Mann

Reproduction in Arctica islandica and its Relationship to the Oceanography of the

Middle Atlantic Bight 119

John J. Manzi, Victor G. Burrell, Jr. and M. Yvonne Bobo

Comparative Gametogenesis in Subtidal and Intertidal Oysters (Crassostrea virginica)

from Bulls Bay, South Carolina 119

Carol A. Moore

Phagocytosis and Degradation of a Unicellular Algae by Hemocytes of the Hard Clam

Mercenaria mercenaria 119

M. P. Morse, W. E. Robinson, W. E. Wehling and S. Libby

A Problem of Giant Seed: A Preliminary Study of the Bay Scallop Argopecten irradians in

Pleasant Bay, Cape Cod 119

Steven A. Murawski, John W. Ropes and Fredric M. Serchuk

Population Biology of the Ocean Quahog in the Middle Atlantic Bight 120

Gary F. Newkirk

Do Fast Growing Oyster Larvae Produce Fast Growing Adult Oysters? 120

/. Ogle and K. Flurry

Studies on Various Substrates in Relation to Setting of Oyster Larvae with Comments

on Commercial Applications 1 20

/. J. Oprandy and P. W. Chang

Evidence for a Virus Causing Neoplasia in the Soft -Shell Clam (Mya arenaria) 120

W. F. Rathjen

Squid Catches Along the United States Continental Slope 121

Donald C. Rhoads, Richard A. Lut: and Robert M. Cerrato

Growth of Mussels at Deep-Sea Hydrothermal Vents Along the Galapagos Rift 121

W. E. Robinson

Statistical Analysis of Digestive Gland Tubule Variability in Mercenaria mercenaria (L.),

Ostrea edulis L., and Mytilus edulis L 121

Oswald A. Roels

The Economics of Artificial Upwelling Mariculture 122

National Shellfisheries Association, Hyannis, Massachusetts Abstracts, 1980 Annual Meeting, June 9-12, 1980 105

CONTENTS (Continued)

John W. Ropes and Steven A. Murawski

Size and Age at Sexual Maturity of Ocean Quahogs Arctica islandica Linne, from a

Deep Oceanic Site 122

N. B. Savage and P. C Clark

Survival of Recent Large Soft-Shell Clam Sets in Hampton-Seabrook Estuary and

Progress to Harvestable Size 122

William N. Shaw

Oyster Setting— Past, Present, and Future 123

Jon G. Stanley, Standish A. Allen and Herbert Hidu

Polyploidy Induced in the Early Embryo of the American Oyster with Cytochalasin B 123

John E. S u pan and E. W. Cake, Jr.

Use of an Oyster Rack for Offbottom Containerized-Relaying of Polluted Oysters

in Mississippi Sound 123

David M. Taylor

An Overview of the Snow Crab (Chionoecetes opilio) Fishery in Newfoundland 124

Rodman E. Taylor

Preliminary Investigations of Local Populations of the Bay Scallop Argopecten irradians

Lamarck in Falmouth, Massachusetts 124

Ronald B. Toll and Steven C. Hess

Methodology for Specific Diagnosis of Cephalopod Remains in Stomach Contents of

Predators with Reference to the Broadbill Swordfish Xiphias gladius 124

Donald J. Trider and John D. Castell

Protein Digestibility in the Lobster Homams americamis 125

K. C. Turner and Robert K. Cox

Seasonal Reproductive Cycle and Show Factor Variation of the Geoduck Clam Panope

generosa (Gould) in British Columbia 125

Michael Vecchione

Aspects of Loligo pealei Early Life History 125

Dennis Walsh

Limitations and Potentials of Bay Scallop (Argopecten irradians) Culture in New England 125

W. E. Wehling, W. E. Robinson and M. P. Morse

Seasonal Variations in Body Component Indices and Energy Stores in the Sea Scallop

Placopecten magellanicus (Gmelin) 126

National Shellfisheries Association. Hvannis, Massachusetts

Abstracts. 1980 Annual Meeting, June 9-1 2, 1980 107

ROLE OF CHEMORECEPTION IN PREDATION BY THE
OYSTER DRILL UROSALPINX CINEREA.

I. FEEDING BEHAVIOR

BETSY BROWN, LESLIE WILLIAMS
AND MELBOURNE R. CARRIKER

University of Delaware,
College of Marine Studies,
Lewes, Delaware 19958

Research has been initiated to investigate the chemical
ecology of feeding behavior in oyster drills, Urosalpinx
cinerea and Ocencbra inomata, as a basis for drill control.
To date, this work has focused on (1) quantifying the
influence which feeding attractants. produced by the oyster
Crassostrea virginica, have on the behavior of U. cinerea,
and (2) isolating additional variables which may significantly
modify feeding behavior.

A Y-maze choice chamber has been designed which tests
quantitatively the response of drills to a variety of stimuli
(such as feeding attractants) presented to them. Observations
on the influence of oyster feeding attractants show that U.
cinerea: (1) preys on oysters reared in the laboratory on a
unialgal diet of the diatom Thalassiosira pscwJonana;
(2) migrates perferentially toward a high biomass of these
oysters; (3) migrates preferentially toward well fed. as
opposed to starved, oysters; (4) has a low frequency (less
than 40%) of response to oysters in the winter under non-
hibernating conditions (20 to 25°C); (5) searches for its
prey most actively at night; (6) is slow in its response to
oyster prey; and (7) feeds sporadically rather than contin-
uously. Results from these experiments will assist in devel-
opment of a rapid screening bioassay to elucidate in more
detail the chemical nature of feeding attractants produced
by oysters.

Originally presented at NSA Annual Meeting, Vancouver, B.C.
August 1979.

NONRADIOLOGICAL STUDIES OF TRAY-HELD OYSTERS,
CRASSOSTREA VIRGINICA, IN THE VICINITY OF THE
CALVERT CLIFFS NUCLEAR POWER PLANT
IN CHESAPEAKE BAY. 1970-1979 1

GEORGE R. ABBE

Academy of Natural Sciences
of Philadelphia, Benedict Estuarine
Research Laboratory,
Benedict, Maryland 20612

Growth and mortality of three age classes of tray-held
oysters, Crassostrea virginica Gmelin, were monitored from
1970 to 1979 at several stations in Chesapeake Bay in the

area of the Baltimore Gas and Electric Company's Calvert
Cliffs Nuclear Power Plant. Additional oysters were
monitored for uptake of copper and nickel.

During the preoperational years (1970—1975), one con-
tinuous study was conducted, but during the operational
period (1975-1979), several separate studies were initiated
because of heavy losses of oysters and research platforms
due to ice.

Station differences in growth and mortality were minimal
during preoperational years, but accelerated growth during
operational years was evident in thermally affected areas.
Overall growth rates during operational years, however,
were not as high as those of 1970—1972. No differences in
mortality rates occurred between the two periods.

Nickel concentrations in oysters showed seasonal effects,
but did not appear to be influenced by the plant. Mean wet-
weight copper concentrations at the plant during the pre-
operational period (59.6 mg/kg), and operational period
(50.6 mg/kg) were both about twice those which occurred
at a control station (29.8 and 19.6 mg/kg) during the same
periods. Thus, the higher concentrations of copper in oysters
at the plant appear to be unrelated to plant operation.

This study was supported by the Baltimore Gas and Electric
Company.

THE SHORT-FINNED SQUID ILLEX ILLECEBROSUS
FISHERY IN EASTERN CANADA

T. AMARATUNGA

Department of Fisheries and Oceans
P.O. Box 550. Halifax, N.S.
Canada B3J 2S7

The squid Illex illecebrosus traditionally had been
important to Canada only as a small inshore fishery in
Newfoundland. Fluctuations in inshore squid landings,
common prior to 1975, probably were related to the avail-
ability of squid. Since 1975, the inshore and offshore
fisheries have shown tremendous increases in landings, and
that has resulted in an upsurge in the economy and effort
in the fishery.

Historic trends related to the inshore fishery are dis-
cussed. Recent statistics on the inshore fishery provide
information on catch, season, area, and gear. Offshore
statistics, prior to 1975, were not completely separated by
species. Statistics compiled on the international and
Canadian offshore fisheries from the FLASH computer
information system provide a monitor of all activities since
1977.

The historic and present state of the fisheries are presented
in relation to the management of the resource.

108 Abstracts, 1980 Annual Meeting, June 9-12, 1980

National Shellfisheries Association. Hyannis, Massachusetts

A STUDY OF THE GROWTH AND FEEDING PARAMETERS

OF THE SHORT-FINNED SQUID ILLEX ILLECEBROSVS

IN RELATION TO A FISHERY MODEL

T. AMARATUNGA

Department of Fisheries and Oceans
PO. Box 550, Halifax, .V.S.
Canada B3J 2S7

Growth curves were determined for Illex illecebrosus
from data collected between 1977 to 1979 from commercial
fishing vessels and research cruises on the Scotian Shelf.
The estimated asymptotic lengths ranged from 232 to
278 mm and 294 to 347 mm for males and females,
respectively, while estimated time of birth was between
December and February. The onset of sexual maturation of
males was recorded at a mean length of 228 mm in late
November; in females, the onset was between late November
3nd early December. Diurnal feeding patterns showed
"recently fed" /. illecebrosus descend from the upper region
of the water column shortly after sunrise. Gut contents
are given and three major prey types, Crustacea, fish, and
squid, are identified. A progression from an exclusively
crustacean diet at squid sizes less than 145 mm to pre-
dominantly squid and fish diets at squid sizes greater than
225 mm was attributed to size-related preference and avail-
ability. Cannibalism was an important phenomenon, while
predation on fish was relatively unimportant. Estimates of
feeding, food conversion, and growth are discussed in
relation to a fishery model.

FACTORS AFFECTING THE DEVELOPMENT OF

MOLLISCAN NEOPLASIA LN THE SOFT-SHELL

CLAM MYA ARESARIA: LNDICATIONS FROM

LABORATORY AND FIELD OBSERVATIONS

RICHARD S. APPELDOORN. 1
ROBERT S. BROWN : AND
KEITH R. COOPER 2

Graduate School of Oceanography .
'Department of Animal Pathology,
University of Rhode Island,
Kingston. Rhode Island 02881

An intensive multidisciplinary investigation of molluscan
neoplasia as it occurs in the soft-shell clam Mya arenaria
has been in progress for the past 4 years. The soft-shell clam

has been found to be particularly susceptible to this disease
and it is an ideal organism to study the factors affecting the
development of neoplasia. The investigation, consisting in
part of a field survey, seasonal sampling, field experiments.
and laboratory transmission experiments, has indicated a
viral etiology of neoplasia. Consistant patterns in the
development and progression of neoplasia have been
observed throughout the various surveys and experiments.
A review of these patterns can elucidate some of the factors
which affect neoplasia development. Four specific factors:
temperature, size, dosage, and stress, have been indicated.
Both cold and warm temperatures seem to suppress the
development and progression of neoplasia. High tempera-
ture may be detrimental to the infecting virus. The mech-
anism whereby cold temperature reduces neoplasia remains
enigmatic, possibly acting on the clam, virus, or both.
Temperature affects are evidenced by an annual biphasic
cycle of neoplasia incidence, and by the scarcity of neoplasia
at the extremities of the geographical distribution of the
soft-shell clam. Neoplasia was not found in newly settled
individuals indicating an age-related or exposure-related
affect. Young clams (< 40 mm) had a significantly lower
incidence of neoplasia compared to adults. Neoplasia has
been successfully transmitted by exposing healthy clams to
the effluent of diseased clams. In replicate experiments, it
was found that the incidence and severity of the developing
neoplasia were dependent upon the effluent concentration.
Evidence for that effect in the field has been observed in
transplant experiments. Transmission studies using healthy
clams held under varying sediment conditions have resulted
in consistant differences between the treatments regarding
neoplasia incidence and severity. The constancy of those
effects suggests that they are nonrandom and predictable.
The factors responsible for the observed differences are as
yet unknown but it is postulated that stress resulting from
certain environmental conditions increases the suscepti-
bility of clams to neoplasia. More prevalent and severe cases
were found in clams kept without sediment, and in very com-
pacted, moderately oiled sediment. In a field experiment,
the incidence and severity of neoplasia developing within
different clam populations were found to be related to the
initial conditions (an index of stress) of each population.
Healthier populations (more weight per size) experienced
reduced neoplasia development. These observations indicate
directions where further research would be useful. Using
direct viral inoculation techniques, controlled laboratory
experiments could resolve some of the mechanisms under-
lying these observations.

National Shellfisheries Association, Hyannis, Massachusetts

Abstracts, 1980 Annual Meeting, June 9-12, 1980 109

ISOLATION, CHARACTERIZATION, AND CONTROL

OF A VIBRIO SP. PATHOGENIC TO CRASSOSTREA

VIRGINICA AND OSTREA EDULIS LARVAE

WALTER J. BLOGOSLAWSKI, 1
STEPHEN T. TETTELBACH, 1 LISA M.
PETTI 2 AND BARRY A.NAWOICHIK 3

1 National Oceanic and A tmospheric

Administration, NMFS, Northeast

Fisheries Center, Milford Laboratory,

Milford, Connecticut 06460; 2 Central

Conneticut State College,

New Britain, Connecticut 06050; and

3 'Northeastern University.

Boston, Massachusetts 021 15

During a disease outbreak at a west coast shellfish
hatchery, ground-up samples of infected Ostrea edulis
larvae and their culture water were pjaced on marine agar.
Of the predominant isolates taken, one was shown consis-
tently to cause greater than 90% mortality to both develop-
ing O. edulis larvae and Crassostrea virginica embryos in
challenge tests. Exponential growth of the suspect bacterium
occurred immediately upon exposure to eggs; embryonic
mortality increased steadily throughout 48-hour challenges.
This bacterium was identified as a member of the genus
Vibrio through a series of over 60 morphological and bio-
chemical tests. Sensitivity to various antibiotics also was
determined. Chlorine, ultraviolet, and ozone were evaluated
as disinfectants for this pathogenic Vibrio which is presently
controlled by ultraviolet treatment of shellfish hatchery
seawater.

ASPECTS OF REPRODUCTION OF HARD CLAMS,

MERCENARIA MERCENARIA, IN GREAT

SOUTH BAY, NEW YORK

V. M. BRJCELJ AND R. E. MALOUF

Marine Sciences Research Center,
State University of New York.
Stony Brook, New York 11794

A spectrophotometry method was developed for rapid
quantification of hard clam (Mercenaria mercenaria) sperm
and egg concentrations. An optimum gamete ratio of
approximately 1.8 x 10 5 sperm per 100 eggs was deter-
mined. Hard clams repeatedly were induced to spawn in the
laboratory. Unfertilized spawned ova ranged in size from
50 to 97 pm, and were characterized by a bimodal size-
frequency distribution. In spite of the high variability in
egg production among individuals, correlation between
size (length) and egg production of clams from Great South
3ay, New York, was signficant; 15 to 25% of the variation

in fecundity was attributable to the difference in size of
clams. Maximum egg production recorded for a single female
over the spawning season was 16.8 million eggs. No signifi-
cant differences in fecundity, size of eggs, or larval survival
were detected between clams from two diverse Bay habitats.
Quantitative comparison between gonads of clams from the
Bay, and those spawned for this study suggested that
laboratory spawning tends to underestimate natural fecun-
dities. The proportion of sexes was approximately equal.
The smallest clam to spawn was a sublegal female 33.1 mm
in length. Seed clams were capable of producing viable spawn
but had extremely low fecundities. The significance of the
results was examined in the context of local management
practices.

POPULATION MAINTENANCE, MANAGEABILITY, AND

UTILIZATION OF INTRODUCED SPECIES: PATHWAYS,

PATTERNS, AND CASE HISTORIES

JAMES T. CARLTON AND
ROGER MANN

Department of Biology, Woods Hole
Oceanographic Institution
Woods Hole, Massachusetts 02543

The intentional or accidental introduction of exotic
species into an ecosystem can be viewed in terms of species
success along sequential pathways that consider (1) the
presence of, or likelihood of establishment of, reproducing
populations; (2) energy inputs required; (3) maintenance
and manageability of the exotic species; (4) economic
or ecological disadvantages, and (5) final management
practices (in terms of continued maintenance or utilization).
Modeling of these pathways permits rapid comparisons of
most case histories of nonnative species introduced into
marine and estuarine waters, and further permits the rapid
identification of both "ideal" pathways (leading to economic
success of a fishery based on an exotic species requiring no
energy inputs), "detrimental" pathways (leading to the
establishment of exotic species harmful to the ecosystem),
and many intermediate stages. Ideal pathways that lead to
economic success thus can be readily framed in terms of
both aquaculture and fishery enhancement; (1) for a species
that does not establish reproducing populations, this path-
way consists of maintenance by seeding (that is not economi-
cally prohibitive), through either protected cultivation
(aquaculture) or by seeding the environment (fishery
enhancement); while (2) for a species that does establish
reproducing populaions, this pathway consists of a species
that does not require management (no energy input or
manipulation by man to maintain the population), is not

110 Abstracts, 1980 Annual Meeting, June 9-12, 1980

National Shellfisheries Association. Hyannis, Massachusetts

detrimental to the ecosystem, and can be utilized in a fishery.
The detrimental status of an exotic species can upon
occasion be dually scored: it may produce conspicuous
changes in the native ecosystem (biologically detrimental)
but it may enhance a local fishery (economically non-
detrimental). Comparisons of case histories of exotic species
in freshwater, terrestrial, and marine environments lead to
the conclusion that nondetrimental and detrimental intro-
ductions in the sea both almost always lead off on an
identical pathway: once established, an exotic species in
the sea is unmanageable in a biological sense (the halting
of reproduction and dispersal cannot be controlled by man),
and this is also the case in some, but not all, land and fresh-
water environments. This phenomenon paradoxically
emphasizes both the far greater potential benefit and danger
of introductions in the ocean than in many land or freshwater
ecosystems.

adductor muscle scar is extremely smooth. The ventral
edge of the myostracum is a narrow transitional zone laid
down in advance of muscle attachment as the muscle
migrates with growth of the animal. Conchlolin patches
commence as a thin granular layer on laths. A band of
ligostracal prisms is deposited in advance of deposition of
ligamental resilium and tensilia as the shell grows. A rugose,
pitted, foliated structure follows this and probably anchors
the mantle isthmus to the shell. The resilium is reinforced
by aragonitic fibers; tensilia lack these. Transitional zones
of granular crystallites join juxtaposed prismatic, foliated,
chalky, and myostracal layers. In young dissoconchs
umbonal plicae strengthen attacltment of the left valve to
the substratum. Microscopic shell annuli are present in the
outer prismatic layer, resilium, chondrophoral and nymphal
ligostraca, and adductor myostraca. The study provides new
insights on shell structure, and suggests profitable avenues
for future research on shell formation.

NEW INFORMATION ON THE FUNCTIONAL
ULTRASTRUCTURE OF THE VALVES OF
THE OYSTER CRASSOSTREA VIRGIMCA

MELBOURNE R. CARR1KER,
ROBERT E. PALMER AND
ROBERT S. PREZANT

College of Marine Studies, University
of Delaware, Lewes. Delaware 19958

The oyster forms most of its shell from three basic
mineralized microstructures (simple calcitic prisms, regularly
and irregularly foliated calcitic laths, and irregular aragonitic
myostracal prisms), their transitional microstructures, and
conchiolinal materials. The periostracum is very thin and
nonmineralized. Prismatic structure is present on both right
and left valves; that of the left valve has been overlooked in
previous studies. Prisms increase in size away from the
margin of the valves. Multilayering of prismatic strata
occurs primarily in the right valve. All shell structure con-
tains organic matrix, but that of prisms is most prominent.
The bulk of both valves consists of regularly foliated and
chalky structure. Laths in the region of valves between the
adductor muscle and ventral edge generally point ventrally:
those between the adductor muscle and hinge are variably
oriented. Motility of mantle on the ventral side may partly
explain this orientation. Chalky shell, composed of blades
and leaflets, bounds a system of pores. The surface of the

GROWTH RATES AND FOULING IN SEDIMENT-FREE R\FT

CULTURLNG OF JUVENILE HARD CLAMS,

MERCESARIA MERCESARIA (L.)

L. R. CONNELL.JR. AND
R. E. LOVELAND

Rutgers University,
Piscataway, New Jersey 08854

Juvenile clams, collected from natural Mercenaria inter-
tidal beds, were transferred to all plastic (PVC) trays which
were suspended from plastic flotation collars in the intake
canal of a nuclear power plant. The clams ranged in size
from 2 to 15 mm in length, and were maintained according
to a size-frequency distribution similar to a natural popula-
tion under study. Mortality over a 5-month period was less
than 10%. in contrast to a mortality rate of nearly 90% for
juveniles in natural beds. The maximum growth rate in
sediment-free trays was 0.4 mm per week which occurred
during September 1979. The influence on the growth rate
of 10-mm clams of fouling organisms attaching to the trays
was examined for screens composed of galvanized hardware
cloth and two commercially available plastic meshes.
Mortality was 5% or less in trays which held sediments in
the range of 0.5 to 1.0 mm grain size, and which were
covered by galvanized-wire mesh.

National SheUfisheries Association, Hyannis, Massachusetts

Abstracts, 1980 Annual Meeting, June 9-12, 1980 111

DIAGNOSIS AND PROGNOSIS OF AN HEMATOPOIETIC

NEOPLASM IN THE SOFT-SHELL CLAM

MY A ARENARIA L.

KEITH R. COOPER 1 AND
ROBERTS. BROWN 2

Department of Pharmacology ,
nomas Jefferson University,
Philadelphia, Pennsylvania 19105, and
"Environmental Review, Environmental
Protection Agency, 401 M. Street,
Washington, D.C. 20460

The severity of a disease can be determined by considering
the number of organ systems involved and/or the degree of
organ damage. The degree of tissue damage generally is
correlated with the health of the animals, the course of the
disease, and the final outcome. Three lustopathologic
methods were employed to diagnose neoplasia in 991 soft-
shell clams, Mya arenaria: (1) bright-field microscopy of
hematoxylin- and eosin-stained tissue sections, (2) phase-
contrast microscopy of fresh hemolymph, (3) bright-field
microscopy of methanol-Glemsa fixed hemolymph. The
accuracy of the blood cytologic techniques when compared
to the histologic tissue diagnosis was 94%. The number of
circulating neoplastic cells (as determined from hemolymph
samples) correlated with the extent of organ system damage.
Five degrees of malignancy (with 5 as the most severe) are
proposed for grading the disease. The higher the malignancy
level the greater the probability of death. Clams diagnosed
at a 4 or 5 malignancy level had 100% mortality and a life
expectancy of less than 6 and 3 months, respectively. An
hematopoietic neoplasm followed one of three courses:

(1) the disease progressed to a higher severity and resulted
in death (this occurred at all degrees of malignancy),

(2) the disease remained at a stable level for up to 10 months
(this occurred at 1,2, and 3 degrees of malignancy), and

(3) the disease diminished in extent or disappeared entirely
(this occurred at 1,2, and 3 degrees of malignancy).

In summary, an hematopoietic neoplasm oiM. mercenaria
can be accurately diagnosed and the severity determined
from hemolymph samples.

THE GEODUCK CLAM FISHERY IN
BRITISH COLUMBIA, CANADA

ROBERT K. COX

Marine Resources Branch,
Ministry of Environment ,
Victoria, British Columbia

Harvesting of subtidal stocks of the geoduck clam Panope
generosa (Gould) in British Columbia began in the fall of

1976. Less than 43.4 metric tons were landed that year
from areas in the Gulf of Georgia. By 1979, landings
increased to 2,405 metric tons, and main fishing effort was
focussed on the western coast of Vancouver Island in
Clayoquot and Barclay sounds. Indications for 1980 are
that the fishery will continue to expand into northern coastal
regions with landing approaching 3,000 metric tons. A quota
of 3,630 metric tons has been set for the fishery. Surveys
to date indicate standing stocks in excess of 80,000 metric
tons. Many coastal areas remain to be surveyed.

The fishery is restricted to diver-harvesters who dig each
clam individually using a high-pressure water jet. Present
harvesting occurs between the 10- to 60-foot level. Average
weight of adult geoducks in British Columbia is 1.1 kilos,
and under good conditions a single diver can harvest 350 kilos
per day.

DEVELOPMENT OF THE NEWFOUNDLAND ILLEX

ILLECEBROSUS FISHERY AND MANAGEMENT

OF THE RESOURCE

E. G. DAWE

Department of Fisheries and Oceans

P. O. Box 566 7, St. John 's, Newfoundland,

Canada A1C 5X1

The Newfoundland squid fishery has experienced unpre-
cedented success in recent years. Nominal catch has increased
continuously since 1974 and reached a record high in 1979.
The greatest proportion of the catch has come from the
Newfoundland inshore jigger fishery, although in recent
years a small proportion has been taken offshore.

Improved market conditions have contributed greatly to
the recent success of this fishery. Traditionally, squid (Illex
illecebrosus) had been sold as bait in the line fishery for cod
in the Northwest Atlantic. Recently, however, a foreign
market for squid as food for human consumption has
developed. Fishermen received higher prices for squid and
more effort was invested in the inshore fishery. Improved
fishing technology and an abundance of squid led to the
high catches in the late 1970's.

The general biology of Illex illecebrosus is outlined, and
factors which affect its distribution and availability are con-
sidered. Annual catches throughout the development of the
fishery are presented. Fluctuations in nominal catch are
related to changes in fishing technology, squid abundance,
and market demand. The forum for management of this
resource also is described and changes in management
initiatives with the recent success of the fishery are discussed.

The success of the Newfoundland squid fishery in recent
years has relied heavily on demand by the Oriental market,
especially Japan, for squid as food. Future success in

112 Abstracts. 1980 Annual Meeting, June 9-12, 1980

National Shellfisheries Association, Hyannis, Massachusetts

marketing Newfoundland squid will depend on the quality
of the product, on the status of fllex illecebrosus as a pre-
ferred species among squids, and on the success of other
squid fisheries. Implications are considered in managing a
fishery which may be limited more by market potential
than availability.

PROGRESS TOWARD VALIDATING THE AGING OF
SHORT-FINNED SQUID USING STATOLITHS

E. G. DAWE

Department of Fisheries and Oceans
P.O. Box 5667, St. John s, Newfoundland.
Canada A 1C 5X1

FORECASTING INSHORE ABUNDANCE OF SQUID

ILLEX ILLECEBROSUS FROM A PRESEASON

BIOMASS SURVEY

E. G. DA WE

Department of Fisheries and Oceans

P. O. Box 556 7, St. John s, Newfoundland,

Canada A1C 5X1

The advance prediction of available biomass is funda-
mental to the management of most fisheries. Conventional
methods are based on calculating the contribution to the
fishery for the next year by the various year classes which
were represented in the catch of the previous year. Such
methods are not applicable to the advance prediction of
biomass of short-finned squid because of its short life cycle.
The life span of fllex illecebrosus is approximately 1 year,
rendering the fishery dependent entirely on new recruits.
This is based on direct estimation of the strength of the
new year-class from a preseason survey.

In 1957, it was suggested that catch rates from otter-trawl
surveys on the Grand Bank in May-June could be used to
forecast inshore abundance of squid at Newfoundland.
Since 1947, information is available on the relationship
between otter-trawl catch rates and inshore abundance
from incidental captures of Illex illecebrosus in spring
gioundfish surveys. Using that relationship, prediction of
inshore abundance generally has been successful, especially
in recent years. However, predictability is not certain and
forecasts have been wrong in some years.

Details of the annual preseason survey are presented
here and criteria for short-term forecasting of inshore
abundance are described. Possible causes of fluctuations in
otter-trawl catch rates and inshore abundance are considered
and the reliability of this relationship is assessed as a means
of prediction. Also, factors are discussed which complicate
the interpretation of forecast information. Prospects are
considered for more reliable predictions with respect to
improvements in survey design and better estimation of
inshore abundance. The possibility also is discussed of
establishing a base for an earlier forecast.

Management of the fishery for the short-finned squid
(Illex illecebrosus) has been hampered by an incomplete
understanding of the biology of the species. Paramount in
this respect is the lack of a valid aging technique, without
which such population parameters as natural mortality,
growth, and recruitment cannot be estimated accurately.

Recently, attention has been focused on the study of
statoliths as a possible means of aging short-finned squid.
The statolith is similar to the teleost otolith in structure,
function, and chemical composition. Growth rings have
been observed in statoliths of Illex illecebrosus, and the
possibility has been investigated of chronological inter-
pretation. Back calculation has shown that ring formation
most closely approximates a daily cycle but poor correla-
tion exists between days elapsed and number of rings
counted. This could be due to inadequacies in preparation
technique, interpretation of rings, or method of validation.
Further, ring formation may be irregular.

The procedure used to prepare statoliths for study, and
the criteria for identification of growth rings are described.
Other possible methods 3re discussed which have been
used to prepare otoliths for aging studies. Data acquired
from two studies are presented and analyzed with respect
to problems in detecting and interpreting growth rings.
Validation is discussed with respect to its limitations as
attempted in those studies, and the relative merits are
assessed of other possible means of validation.

GROWTH OF SIBLING HARD CLAMS. \1ERCE.\AR1A

MERCE.\ARIA, IN A CONTROLLED

ENVIRONMENT

N. DEAN DEY

Center for Mariculture Research
University of Delaware
Lewes. Delaware 19958

Sibling populations of clams were raised in a controlled
environment with excess algal food. Within each population
wide variations among individuals were observed in shell
length and volume. Given populations were divided at an
early stage into five successively larger size classes. It was
found that clams in the larger size classes always grew at a
much more rapid rate than smaller clams at both 18°C and
25°C.

National Shellfisheries Association, Hyannis, Massachusetts

Abstracts, 1980 Annual Meeting, June 9-12, 1980 113

Sibling populations in the laboratory exhibit an obvious
nonnormal distribution in shell length within a few days of
spawning. Setting time may be used to further subdivide
the population within each size class. Early-setting clams
grow at a more rapid rate than late-setting clams and
comprise only a small fraction of the population.

Size-frequency distribution of a sibling clam population
maintained in the laboratory is strongly skewed toward the
larger sizes. Such a size-frequency distribution pattern is
observed in hatchery-raised populations for at least a year
after setting, indicating that the late-setting clams never
match the growth rate of the early-setting clams and,
consequently, remain small relative to their larger siblings.

Clam growth in the laboratory during the first 2 months
after setting is composed of three distinct periods, each
with a characteristic growth rate. During the first 4 weeks,
growth of spat continues at the larval rate. This rate of
increase then decreases (growth pause) for the next 2 weeks.
Following the growth pause, rapid growth resumes, although
at a reduced rate typical of juvenile clams. The growth
pause may be associated with growth of the siphons.

With proper selection of early-setting larvae, fast-growing
commercial strains, as well as uniform groups of clams, may
be produced for studies in such fields as toxicology and
nutrition. In hatchery operations, where initial larvae num-
bers are large, experience indicates that fast-growing larvae
comprise fewer than 5% of the population.

exclusion test was useful in demonstrating early signs of
the disease such as detached mantle and velar cells. Histo-
logical examination demonstrated attachment of bacteria to
the larval shell and its growth through the mantle into the
visceral cavity. Extensive vacuolation of digestive system
organs, apparently related to lipid retention, also was a
consistent feature of the disease. The F/in'o-specific fluores-
cent antibody test provided rapid identification of the
etiologic agent.

The possible relationship of a nutritional imbalance,
signaled by the vacuolation of the digestive tract organs,
to a too rapid growth rate and low production is discussed.
The trypan blue dye exclusion test proved to be a useful
hatchery management tool for assessment of larval health.
The fluorescent antibody test, while rapid and highly
specific, is suited for laboratory use only. The pathogenesis
of vibriosis in this commercial hatchery epizootic was
identical to that previously described in experimental
vibriosis.

*This research was sponsored by the New York Sea Grant Institute
under a grant from the Office of Sea Grant, National Oceanic and
Atmospheric Administration, U.S. Department of Commerce.

REPRODUCTIVE RESPONSE TO INCREASED DENSITY:
SOME OBSERVATIONS FROM MOLLUSCS

DIAGNOSIS OF VIBRIOSIS IN A COMMERCIAL OYSTER
HATCHERY EPIZOOTIC, A CASE HISTORY*

R. ELSTON ' , L. LEIBOVITZ ' ,
D. RELYEA 2 AND J. ZATILA 2

Department of Avian and Aquatic
Animal Medicine, New York State
College of Veterinary Medicine
Cornell University,

Ithaca, New York 15853; and 2 Frank M.
Flower Oyster Company,
Bayville, New York 11 709

A case of epizootic vibriosis of American oyster larvae,
Crassostrea virginica, in a commercial oyster hatchery is
described from both hatchery records and observations,
and by using laboratory diagnostic tools. Hatchery produc-
tion of oyster larvae for the 1979 season was only half
that of the 1978 season. This resulted primarily from a
severe 6-week depression in hatchery output in the spring
of 1979. Larvae from 2 of the 6 weekly spawns during that
period were examined in the laboratory using interference
microscopy, the trypan blue dye exclusion test, histological
methods, and the fluorescent antibody test. The dye

ARNOLD G. EVERSOLE 1 , PETER J.
ELDRIDGE 2 AND WILLIAM K.
MICHENER 1

Department of Entomology and
Economic Zoology, Clemson University.
Clemson, South Carolina 29631; and

National Marine Fisheries Service,
NOAA, Southeast Fisheries Center
Charleston, South Carolina 29412

Increased population density is known to influence
growth and fecundity in molluscs. Few reports exist for
bivalves, and most of those neglect the reproductive response
accompanying reduced growth with increased density.
Recent studies have demonstrated a significant density-
dependent reduction in growth of hard clams {Mercenaria
mercenaria); however, histological evidence has provided
no indication that gametogenesis has been affected by
increased density. In the present study, the amount of
gonadal tissue in clams grown at three population densities
were compared. Clams at the lowest density were larger,
weighed more, and had more gonadal tissue than clams
from higher densities. Gonadal-somatic indices indicated
that the density-dependent reduction of growth did not
fully account for the reductions in the amount of gonadal

114 Abstracts, 1980 Annual Meeting, June 9-12, 1980

National Shellfisheries Association, Hyannis. Massachusetts

tissue. These results are discussed in relation to existing
literature on density-dependent changes in the reproductive
biology of molluscs with emphasis on ecological advantages
and consequences of some changes.

AN APPARATUS FOR THE MEASUREMENT OF GRAZING

ACTIVITY OF FILTER FEEDERS AT CONSTANT

FOOD CONCENTRATIONS*

SCOTT M. GALLAGER AND
ROGER MANN

Department of Biology . Woods Hole
Oceanographic Institution
Woods Hole, Massachusetts 02543

AN INVESTIGATION OF SEA SCALLOPS (PLACEOPECTEN

MAGELLANICUS) OF THE MID-ATLANTIC FROM

COMMERCIAL SAMPLES IN 1979

LOWELL W. FRITZ AND
DEXTER S. HAVEN

Virginia Institute of Marine Science,
Gloucester Point, Virginia 23062

Bushel samples of sea scallops (Placopecten magellanicus)
for height-frequency analysis were obtained aboard the
commercial scalloper VIRGINIA SURF from the mid-
Atlantic region on two trips during the summer of 1979.
Fishing effort was concentrated in three areas of the shelf:

(1) 60 miles east of the Virginia-North Carolina border,

(2) 70 miles east of the coast from Cape Henlopen, Delaware,
to Atlantic City, New Jersey, and (3) 45 miles south of
Long Island from Moriches Bay to Bridge Hampton. Indi-
viduals (214), ranging in size from 60 to 149 mm shell
height, were retained for age analysis from the catches of
the two northern areas.

The mean size of scallops caught in the southern region
of the mid-Atlantic was smaller than those caught in the
northern region. Ninety percent of the southern scallops
measured were between 75 to 119 mm shell height with a
peak occurring between 95 to 99 mm. A peak in height
frequency for the two northern samples occurred at 1 10 to
1 14 mm, and 90% of the scallops measured ranged between
95 to 134 mm. Most of the scallops represented by the
peak in the southern sample were of the 1975 year-class,
while the northern sample peak was composed of the
1972—1974 year classes. Smaller, younger scallops appeared
more frequently in the southern area, possibly indicating
more successful recruitment since 1975 than in the northern
areas samples.

Catch-per-unit of effort (pounds per paired 15-foot
dredge tow) was higher in the southern (41.3) area than
in either of the two northern areas (20 and 30.8,
respectively).

An apparatus is described which measures the grazing
activity of filter feeding invertebrate larvae and adults in an
environment in which the phytoplankton food concentration
can be maintained at a constant level. The "sensing" portion
of the apparatus consists of a Model III Turner fluorometer
equipped with a modified flow-through door. Sensitivities
of ± 1 % of a selected phytoplankton concentration were
achieved in experiments in which the flagellate Isochrysis
galbana was fed to larvae of the bivalves. Teredo navalis
and Mytihis eclulis, the gastropod, Aplysia califoniica, and
adults of the copepod, Acartia tonsa. The apparatus can be
used effectively with as few as 100 mollusc larvae.

*This work was supported by Office of Naval Research Contract
N00014-79-C-0071 NR 083-004.

INTERTIDAL GROWTH IN MYTILUS EDULIS L. 1

R. B. GILLMOR 2

Department of Oceanography ,
University of Maine at Orono,
Walpole, Maine 04573

Although a number of commercially important bivalve
species occur intertidally and, in some instances, are actively
cultured on the shore, no study has investigated systemati-
cally the growth responses of bivalves to intertidal exposure.
This paper reports some results of an initial attempt at such
an investigation, and focuses in particular on the blue mussel
Mytilus edulis.

Several hypothetical curves are considered relating
instantaneous growth rate to shore level (expressed as
percent aerial exposure). Energy-conserving adaptations,
decreasing energy losses which are a consequence of inter-
tidal exposure, will produce growth curves having greater
x-intercept values, i.e., higher shore levels where growth
goes to zero. The presence of energy -supplementing adapta-
tions that compensate, to some extent, for the tidally
restricted time available for feeding, will be apparent in
nonlinear growth curves, convex upward.

The integral of a growth curve over the range of exposures
for which growth is positive, a value referred to as the

National Shellfishcries Association, Hyannis, Massachusetts

Abstracts. 1980 Annual Meeting. June 9- 12. 1980 115

intertidal scope for growth, reflects the energetic contribu-
tions made by both types of adaptation and may be used in
comparative work among intertidal suspension feeders. The
intertidal scope for growth will be minimal when growth is
not possible at any level on the shore, and maximal when
intertidal growth equals subtidal growth at all shore levels.

Instantaneous growth curves for M. edulis juveniles
subjected to known levels of aerial exposure were derived
from data on changes in dry meat weight, dry shell weight,
length, and width. Experiments were run in the laboratory
as well as on a natural shore. Both sets of curves showed a
bilinear, convex-upward form, indicating compensation
mav have occurred. Growth in the laboratory decreased
slowly with increasing exposure up to the 40% exposure
level, and more rapidly thereafter, falling to zero at 90%
exposure (for dry meat weight). On the shore, growth
declined more rapidly at exposure levels greater than 20%,
going to zero at about 80% exposure

The lower x-intercept value for the shore-grown mussels
indicated higher intertidal energy losses in that group
compared with the laboratory group. Despite these higher
losses, both groups had similar intertidal scopes for growth,
about one half of the theoretical maximum. This implies
that energy supplementation in Mytilus just balances inter-
tidal energy losses so that, overall, growth performance
simply reflects the limitations placed on feeding time.
This result is contrasted with that obtained for Ostrea edulis,
a low-shore species in which no compensating ability is
apparent and a doubling of energy losses in going from
laboratory to shore conditions reduces the intertidal scope
for growth from one-third to one-fourth the theoretical
maximum, a drop of 25%.

Also noted was the higher meat-to-shell ratio of inter-
tidal mussels, and their thicker and more globose shells, as
compared to subtidal specimens.

1 Winner of the Thuriow C. Nelson Award for the outstanding paper

by a student or junior scientist.
2 Present address: EG&G Environmental Consultants, 300 Bear Hill

Road, Waltham. Massachusetts 02154.

PRELIMINARY CHEMICAL CHARACTERIZATION OF

MANTLE CAVITY FLUID OF THE OYSTER

CRASSOSTREA VIRGINICA

JULIUS GORDON, DANIEL
RITTSCHOF, LESLIE WILLIAMS AND
MELBOURNE R. CARRJKER

College of Marine Studies
University of Delaware
Lewes. Delaware 19958

Previous investigations have shown that Crassosrrea
virginica releases chemical stimuli that attract its larvae
as well as predators and scavengers such as llyanassa obsoleta,
Astenas forbesi. and A. vulgaris. Many behavioral investi-
gations have inferred that such stimuli also attract oyster
drills. Urosalpinx cinerea and Ocenebra inornata (=japonica).
The purpose of the present investigation was to identify
and characterize chemical substances present in seawater
filtered by C. virginica (mantle cavity fluid) that may be
primary chemical attractants to oyster drills such as
U. cinerea and O. inornata.

Mantle cavity fluid was sampled directly from the supra-
branchial cavity with a hypodermic needle placed between
the valves of an actively pumping oyster dorsal to the
rectum, or indirectly by collection of aquarium water in
which oysters had been feeding actively for 24 to 36 hours.
Samples were then concentrated by pressure dialysis, and
characterized by means of gel filtration, thin layer chroma-
tography, and gel electrophoresis.

Results of gel filtration show two peaks of ultraviolet
(UV) absorbing material, representing fractions with
molecular weights greater than 67 K daltons and less than
1 K daltons, respectively. Thin layer chromatographic results
show that one substance occurring in mantle cavity fluid
is hydrophilic and behaves as a protein or peptide, while
a second substance appears neutral or hydrophobic. Results
from gel electrophoresis revealed low concentrations of
3 to 4 peptides (20,000 to 46,000 daltons), and high con-
centration of a PAS positive and Coomassie Blue negative
substance believed to be mucopolysaccharide. The PAS
positive material occurs in two major bands, 400 K and
200 K daltons, that degrade into 60 K and 30 to 40 K sub-
units. Carbohydrate analysis reveals 0.3 to 4.7 ng carbo-
hydrate per ml mantle cavity fluid measured as galactose
equivalents. 0.5 to 1 .4 jug/ml hexose amine. 0.1 to 0.7 jig/ml
hexuronic acid, and 0.2 to 7.0 jug/ml hexamine. Only trace
quantities of protein were present (0.03 to 0.06 Mg/ml).
Additional studies are needed to investigate the carbohy-
drate constituent of mantle cavity fluid in more detail as
well as examine its efficacy in attracting the oyster drill
Urosalpinx cinerea.

116 Abstracts, 1980 Annual Meeting, June 9- 12, 1980

National Shellfisheries Association, Hyannis, Massachusetts

MYA 4«£,V.4/?M-N0N0BL1GATE INFAUNA

HERBERT H1DU

Ira C. Darling Center
Walpole, Maine 045 73

Natural adult soft-shell clams that are removed from
their burrows to trays will regress and eventually die.
Hatchery-reared clams, however, confined exclusively in a
nonsediment environment, exhibit considerable change in
shell allometry and outperform sibling infaunal groups.
After 2 years the trayed clams showed similar mean lengths
as the infaunaJ groups; however, they exhibited a significant
increase in degree of shell inflation, shell weight, and dried
meat weight. These findings are discussed in the general
context of life habitat of bivalve molluscs, and for the
importance they may hold as a research tool and in com-
mercial mariculture.

A COMPARISON OF FEEDING AND GROWTH IN NATURAL
AND CAPTIVE SQUID (ILLEX ILLECEBROSUS)

ROY W. M. HIRTLE .AND
RONALD K. O'DOR

Biology Department .
Dalhousie University,
Halifax. .V.S., Canada B3H 4J1

With the rapid development of the international fishery
directed toward the short-finned squid, the biology of the
species has received increased attention. Investigations of
the physiology of feeding and growth of these squid were
conducted in the 15-m circular pool in the Aquatron
Laboratory of Dalhousie University in 1978 and 197**.

Squid, captured locally in a net trap, ranged in size from
70 to 250 g ( 16 to 25 cm mantle length), and fed ad libitum.
For whole schools daily feeding rate to supply maintenance
requirements was 1 to 2% of body weight (BW). Daily
feeding rates of 3.6 to 7.8% BW yielded daily growth rates
of 1.0 to 2.2% BW. and varied with size and temperature.
Conversion (growth) efficiency ranged from 35 to 60%,
after allowing for maintenance. These ranges of values held
for both fish and crustacean diets.

Observations on individual squid suggest that they grow
most efficiently at daily feeding rates of about 10% of body
weight. A simple nonlinear model fitted to data conforms
to this estimate, and indicates decreased growth efficiency
at higher feeding r3tes.

Lower growth rates in the natural population suggest
that food supply becomes increasingly limited as the season
progresses. Most of the natural population biomass results
from feeding before July when crustaceans are the principal

prey; feeding rates are lower in late summer. Captive squid
begin to cannibalize smaller or less healthy individuals after
3 to 5 days of starvation, and cannibalism could be an
important nutrient reserve when other food is lacking,
particularly during spawning migrations.

GROWTH, FECUNDITY AND ESTIMATED LIFE SPAN

OF THREE LOLIGINID SQUID SPECIES IN THE

NORTHWESTERN GULF OF MEXICO

R. F. HIXON, R. T. HANLON
.AND W. H. HULET

Vie Marine Biomedical Institute
University of Texas
Galveston. Texas 77550

Growth of Lolliguncula brevis, Loligo plei, and Loligo
pealei was estimated from ( 1 ) length-frequency analyses of
seasonal trawl samples. (2) laboratory-rearing studies, and
(3) maximal size and proposed age estimates. Using these
estimates, growth rates of Lolliguncula brevis ranged
between 0.0 and 21.4 mm per month,/,, plei from -7.0 to
59.0 mm per month, and L. pealei from 6.5 to 60.0 mm per
month. In general, maximal growth rates observed in the
laboratory were double those derived from trawl data.
Fecundity was estimated from laboratory observations of
spawning females. Two L. pealei produced four separate
broods of eggs totaling 2 1 .000 and 53,000 eggs, respectively,
and one Lolliguncula brevis spawned 2.000 eggs in a single
brood. The life span of all three species in the northwestern
Gulf of Mexico was estimated to be approximately 1 year,
with a few individuals surviving up to 18 months.

PRELIMINARY NOTES ON A PILOT PLANT FOR THE
FEEDING OF ADULT AMERICAN OYSTERS

R. M. INGLE, D. G. MEYER
.AND M. R. LANDRUM

Adelanto Corporation
Apalachicola, Florida

Based on previous work showing the efficacy of using
finely ground cornmeal as a food to increase the quality of
oysters, a plant was constructed to adapt the methods,
previously developed on a laboratory scale, to more nearly
commercial levels. Results of initial experiments in the
facility corresponded to those previously carried out in the
laboratory. Experiments were of 2 to 3 weeks duration.
Percent glycogen of dried oyster meats increased dramatically
but, in general, increases were less impressive as feeding
continued. The cornmeal slurry was delivered to the oysters

National Shelli'isheries Association, Hyannis, Massachusetts

Abstracts, 1980 Annual Meeting, June 9-12, 1980 117

in a semi-recirculating system showed a build up of bacteria
which was reflected at times by somewhat less pronounced
high counts in tank water. However, oyster bacterial counts
were high whether feed was added or not. Yield increase
appeared to vary inversely as salinity, independent of the
glycogen content. Yield increases due to osmotic effects
could be expected to be transient while those resulting
from glycogen increases could be considered more stable.
At present, the details of the nutritional mechanisms are
not understood. Oysters have been thought to accept only
small-size particles, perhaps less than 60 /j. Examination of
cornmeal used in feeding was found to consist of compo-
nents 87% of which would not pass through a 70-jlx screen.

REPRODUCTIVE CYCLES OF THE OCEAN QUAHOG

ARCTICA ISLANDICA AND THE ATLANTIC

SURF CLAM SPISULA SOLIDISSIMA OFF

NEW JERSEY

DOUGLAS S. JONES

Department of Geology,
University of Florida,
Gainesville, Florida 32611

The annual reproductive cycles of the two commercially
important bivalves Spisula solidissima, the Atlantic surf
clam, and Arctica islandica, the ocean quahog, were investi-
gated using specimens collected from the New Jersey coast.
For two consecutive years, April 1977 through March 1979,
specimens of both species were recovered from commercial
port landings at biweekly or monthly (during winter)
intervals. Gonads of the 324 surf clams and 320 ocean
quahogs were examined histologically.

By late May or June, the gonads of Spisula solidissima
were characterized by morphologically ripe eggs or sperm.
The percentage of individuals with partially spawned gonads
rose sharply in the late summer and, by November or
December, 100% appeared spent. Gametogenesis then
proceeded slowly over the winter months, speeding up in
the spring. The sex ratio of the surf clams analyzed was
exactly 1:1.

A somewhat similar pattern was exhibited by Arctica
islandica. The percentage of individuals with ripe eggs or
sperm rose steadily from May (< 10%) to August (~ 100%).
During the first year partially spawned clams predominated
in September and October before spawning out by late
November. In the second year, partially spawned or spent
individuals persisted into early February. Gametogenesis
progressed slowly in the winter and more rapidly in the
spring. Of the 320 ocean quahogs analyzed, 58% were males.

Temporal differences between the reproductive cycles
of consecutive years may be related to differences in marine
temperatures. Comparison of the results achieved here with
previously published studies indicates important similarities
and differences, and the need for further work.

SHELLFISH PROPAGATION ON MARTHA'S VINEYARD

RICHARD C. KARNEY

Martha 's Vineyard Shellfish Group
Oak Bluffs. Massachusetts 02557

The Martha's Vineyard Shellfish Group, a consortium of
the shellfish departments of five island towns, has initiated
a program to improve and expand the traditional shell-
fisheries in the waters of the member towns under funding
from the Economic Development Administration. For
4 years, our program of community resource development
has concentrated on nursery-raft culture methods for
hatchery-reared seed quahogs, Mercenaria mercenaria. Of
various raft designs tested, economical, sand-filled wooden
trays suspended from floats gave the best growth and
survival. We observed over 80% survival of 480,000 seed
quahogs raft-cultured in 1979. Seed quahogs as small as
2 mm have been successfully cultured in the nursery rafts.
The survival of raft-cultured quahogs (12 to 25 mm)
seeded in natural beds also is under investigation.

The bay scallop Argopecten irradians supports an
important island fishery providing employment in the off-
season when tourist dollars are scarce. Preliminary work
suggests that maintaining an adult spawning population in
backwater areas can help stabilize harvest in ponds where
strong circulation patterns frequently flush larvae from the
ponds before they set.

Seed quahogs and scallops have been produced in the
Group's small pilot hatchery. During the summer of 1979,
we spawned and cultured scallops through larval and post-
set stages in the hatchery, and at 2 mm moved them to
experimental floats in the pond. Over 230,000 of the lab-
spawned and cultured scallops (12 mm and greater) were
seeded in natural and experimental beds in the five-town
waters.

As part of our hatchery work, we crossed orange-shelled
scallops in the hope of developing a genetically tagged
scallop to be used as a research tool in studying larval move-
ments in the field. About 80% of the F, generation of
orange parents exhibited orange-shell color.

118 Abstracts, 1980 Annual Meeting, June 9-12, 1980

National Shellfisheries Association, Hyannis, Massachusetts

WATER CIRCULATION AND OYSTER SPAT SETTLEMENT

IN TWO ADJACENT TRIBUTARIES OF THE

CHOPTANK RD/ER, MARYLAND

VICTOR S.KENNEDY 1 AND
WILLIAM C. BOICOURT 2

Horn Point Environmental Labs,
Cambridge, Maryland 21613, and

Chesapeake Bay Institute,
Shady side, Maryland 20867

species was developed by distant water fleets, and catches
increased to an average of 45,000 metric tons a year
(1969-1978).

Management of these fisheries began in 1974, under
ICNAF, with establishment of a preemptive quota for the
entire squid catch. Subsequently, separate quotas have been
established for each species. Since 1977, under the Fisheries
Conservation and Management Act, the United States has
had management jurisdiction over those stocks. Since 1977,
total catches of both species have declined sharply.

Studies of water circulation in Chesapeake Bay tribu-
taries, which have had consistently good oyster spat settle-
ment success, have indicated that hydrographic (advective
and dispersive) conditions may act to retain larvae in the
system. There has been no study of an area with poor
settlement success. Broad Creek and Tred Avon River are
adjacent tributaries with good and poor oyster spat settle-
ment success, respectively. Many physical factors (tempera-
ture, salinity, tidal range, dissolved oxygen) and biological
factors (adult sex ratios and gametogenic patterns) generally
are similar in both tributaries. An intensive study employing
current measurements and dye diffusion experiments was
performed in early July 1979, while oyster larvae were in
the water column and setting in both tributaries. The results
of that study revealed circulation differences between both
tributaries and suggested that flow variability may be as
important as mean motion in affecting larval distribution.

HISTORY AND PRESENT CONDITIONS OF SQUID,

LOLIGO PEALEl AND ILLEX ILLECEBROSUS,

FISHERIES OFF THE NORTHEASTERN

COAST OF THE UNITED STATES

A. M. T. LANGE

National Marine Fisheries Service,
Northeast Fisheries Center,
Woods Hole Laboratory
Woods Hole, Massachusetts 02543

The fishery for squids, Loligo pealci and Illex illecebrosus,
in the Northwest Atlantic, off the northeastern United
States, has undergone significant changes over the past
decade. Annual catches by the domestic fleet (primarily
incidental to other directed fisheries) averaged between
1,000 and 2,000 metric tons during the period from 1887
to 1967. However, in 1967, a directed fishery for those

YIELD-PER-RECRUIT ANALYSIS FOR SQUID, LOLIGO

PEALEl AND ILLEX ILLECEBROSUS, FROM

THE NORTHWEST ATLANTIC

A. M. T. LANGE

National Marine Fisheries Service
Northeast Fisheries Center
Woods Hole Laboratory
Woods Hole, Massachusetts 02543

Yield-per-recruit analyses of squid, Loligo pealei and
Illex illecebrosus, were conducted based on representations
of their life history and the fisheries for them. Each species
has an extended (about 6 months) spawning season, resulting
in significant differences in growth and mortality to different
segments of a year-class. Two cohorts were, therefore,
assumed for each year-class, one hatched early in the
season, and the second hatched later, to account for such
differences.

A modified Ricker yield-per-recuit model was used to
analyse the differences in varying levels of fishing and
natural mortality rates on these stocks. Instantaneous
growth, and relative fishing and spawning mortalities were
varied on a monthly basis to represent their effects on each
proposed cohort, for several sets of natural and total
mortalities. Several assumptions of year-class cohort struc-
ture were made (percent of cohort spawned early in the
season) to determine the significance of time of spawning
on potential yields. Effects of increasing size of entry to the
fishery by increasing mesh size also were examined.

Yield-per-recruit for both L. pealei and /. illecebrosus
was found to increase for all assumptions of fishing and
natural mortality rates, and for time of spawning when
mesh sizes were increased to 60 mm (from 15 mm). Further
increases in yield were calculated when the mesh size was
raised to 1 '0 mm.

National Shellfisheries Association, Hyannis, Massachusetts

Abstracts. 1980 Annual Meeting, June 9-12. 1980 119

REPRODUCTION IN ARCTICA ISLANDICA AND ITS

RELATIONSHIP TO THE OCEANOGRAPHY OF

THE MIDDLE ATLANTIC BIGHT

ROGER MANN

Department of Biology

Woods Hole Oceanographie Institute

Woods Hole, Massachusetts 02543

A review is made of the present knowledge of the biology
of Arctica islandica with special reference to the reproductive
cycle. Arctica islandica extends throughout a range in the
Middle Atlantic Bight which is noted for seasonal thermal
stratification of the water column. It is hypothesized that
the intense summer thermocline forms an effective barrier
to larval dispersion during the summer months, and that the
functional reproductive period of this species occurs during
the late fall and winter months and not in the late summer.
The implications of this hypothesis on the range of larval
dispersion in A. islandica are discussed. A continuing program
of research to test this hypothesis is described.

COMPARATIVE GAMETOGENESIS IN SUBTIDAL AND

INTERTIDAL OYSTERS (CRASSOSTREA VIRGINICA)

FROM BULLS BAY, SOUTH CAROLINA

JOHN J. MANZI, VICTOR G.
BURRELL, JR. AND
M. YVONNE BOBO

Marine Resources Research Institute
Charleston, South Carolina 29412

temporal patterns in development and appeared to spawn
during the same periods.

A proposed index for gametogenesis in southern oysters
is described, and gametogenic progression in subtidal and
intertidal populations is discussed.

PHAGOCYTOSIS AND DEGRADATION OF A UNICELLULAR

ALGAE BY HEMOCYTES OF THE HARD CLAM

MERCENARIA MERCENARIA

CAROL A. MOORE

Marine Science Institute
Northeastern University
Nahant, Massachusetts 01908

Hemocytes of the hard clam Mercenaria mercenaria were
observed to phagocytize Isochrysis galbana and several
other species of unicellular algae , as well as congo red-stained
yeast. The "blunt" cytoplasmic granules were shown to
receive degraded materials from the phagosomes containing
the algae but not those enclosing a yeast cell. Transfer of
the degradation product(s) was traced by observing visually
the fluorescence emission of the phagocytized material, and
by spectral analysis with a microspectrofluorimeter. Blunt
granules were further observed to participate in the intra-
cellular processing of the hemocyte of vital dyes and endo-
toxin. Observations at the light microscopy level have
been correlated with ultrastructural data. It is suggested
that the blunt granules represent a mechanism whereby the
hemocytes can contain and/or further degrade foreign
material.

Subtidal and intertidal oysters were collected monthly
from December 1977 to January 1979 at two tidal marsh
creeks in the Bulls Bay area of the South Carolina coast.
Whole shucked oysters were fixed in FAA, gonadal tissue
was excised, dehydrated in alcohol, cleared in toluene, and
infiltrated in 57°C paraplast. Longitudinal and serial cross
sections were made of each gonad at 1-n on a rotary micro-
tome, stained with Gill's hematoxylin, counterstained with
eosin, and examined at 100X and 400X with a light
microscope.

Initial observations indicated the inadequacies of estab-
lished gametogenic indices for mollusca, and necessitated
the formulation of an index suitable for the prolonged
spawning periods and reduced inactive period characterized
by the southern oyster. The application of this index, incor-
porating even stages of gametogenesis (one inactive, two
primary, two secondary, and two tertiary) indicated little
difference between gametogenic progression in intertidal
and subtidal oysters. Both populations exhibited the same

A PROBLEM OF GIANT SEED: A PRELIMINARY STUDY OF

THE BAY SCALLOP ARGOPECTEN IRRADIANS IN

PLEASANT BAY, CAPE COD

M. P. MORSE 1 , W. E. ROBINSON 1 ,
W. E. WEHLING 1 AND S. LIBBY 2

Marine Science Institute,
Northeastern University,
Nahant, Massachusetts 01908, and

Shellfish Department
Town of Orleans, Massachusetts 02653

In the winter of 1979, the population of bay scallops
Argopecten irradians in Pleasant Bay, Massachusetts, was
dominated by large individuals without a well-defined
raised annulus or growth line. According to the legal
definition, these animals were considered large seed scallops
and, thus, were protected from being harvested. Atypically,
relatively few scallops were present which possessed a well

120 Abstracts, 1980 Annual Meeting, June 9-12, 1980

National Shellfisheries Association, Hyannis, Massachusetts

defined annulus of any kind. Those that did have an annulus
could be classified into one of two groups: those with an
annulus close to the hinge line and those with an annulus
approximately 1-1/5-inch to 1-3/5-inch from the hinge line.
Scallops from all three groups were approximately the same
size. Large seed scallops generally had a glossy black covering
over the gonads. The other two groups showed variable
coloration. Histological analysis of gonadal material from
January 1980 samples indicated that gametogenesis had
begun in all three groups of scallops. Periodic sampling of
scallops, and monitoring of the gametogenic cycle are
currently being conducted to assess the value of these large
seed scallops in the overall scallop population of Pleasant
Bay.

POPULATION BIOLOGY OF THE OCEAN QUAHOG IN
THE MIDDLE ATLANTIC BIGHT

STEVEN A. MURAWSKI, JOHN W.
ROPES AND FREDRIC M. SERCHUK

National Marine Fisheries Service,
Northeast Fisheries Center
Woods Hole, Massachusetts 02543

The ocean quahog Arctica islandica has become increas-
ingly important to the clam industry of the United States.
Landings of shucked meat increased thirty-fold between
1975 and 1979;from570 metric tons to 15,610 metric tons.
Data on the distribution, relative abundance, and size com-
positions of Middle Atlantic stocks have been gathered
during a series of dredge surveys since 1965. Additional
information on age and growth is available from recent
field and laboratory studies. A review of important biologi-
cal features, and a current assessment of Middle Atlantic
populations are presented.

DO FAST GROWING OYSTER LARVAE PRODUCE
FAST GROWING ADULT OYSTERS?

GARY F. NEWKIRK

Biology Department,
Dalhousie University
Halifax, N.S., Canada B3H 4J1

In several lines of European oysters, Ostrea edulis, the
correlation between larval growth rate and juvenile size
(mean length = 22 mm) is positive but small. As the oysters
continue to grow, the effect of larval growth rate diminishes;
it is virtually zero by the time the oysters are 43 mm,
average size. In one line, the correlation remained nonzero
for 2 years, but was so small that very little of the variation

in size could be attributed to variation in larval growth rate.
Consequently, it appears there is little to be gained in
improving juvenile and adult growth rates by selecting
faster growing larvae. Selecting faster growing larvae may
improve hatchery performance, but to improve growout,
selection must be done at a later stage.

STUDIES ON VARIOUS SUBSTRATES IN RELATION TO

SETTING OF OYSTER LARVAE WITH COMMENTS

ON COMMERCIAL APPLICATIONS

J. OGLE AND K. FLURRY

Oyster Biology Section,

Gulf Coast Research Laboratory

Ocean Springs, Mississipppi 35964

Setting oysters in a hatchery along the Gulf of Mexico
must be inexpensive and adaptive to bottom planting to be
competitive with natural setting. Preference of oyster larvae
for setting on clam shell was compared to three other
substrates in the laboratory; however, many larvae (57%)
were "lost" to the tanks and containers. Setting on oyster
valves was comparable whether the shells were held in boxes
or bags. Freshly shucked "green" shells, aged shells, and
washed oyster valves caught spat equally well when planted
in the bay. However, in the hatchery, washed shells caught
three times as many spat as did aged shells and sixteen times
as many spat as "green" shells. A system for handling the
required volumes of clam shell for setting hatchery-reared
larvae is proposed for a pilot seed operation.

EVIDENCE FOR A VIRUS CAUSING NEOPLASIA IN THE
SOFT-SHELL CLAM (MY A ARENARIA)

J. J. OPRANDY AND P. W. CHANG

Department of Aquaculture Science
and Pathology
University of Rhode Island
Kingston, Rhode Island 02881

Hematopoietic neoplasia is a terminal cancer of the
hemocytes of soft -shell clams (Myaarenaria), and is endemic
to the northeastern United States. No association has been
made between bacteria, mycoplasmas, or protozoan parasites
and the disease, nor has there been any correlation with
environmental pollution.

We have isolated a virus from neoplastic soft-shell clams
with physical and chemical properties similar to RNA tumor
viruses. Further, neoplasia has been induced upon injection
of the purified virus into nonneoplastic clams. RNA tumor
viruses have long been associated with neoplasms in mice.

National Shellfisheries Association, Hyannis, Massachusetts

Abstracts, 1980 Annual Meeting, June 9-12, 1980 121

cats, and fowl. Virus has not been isolated from any non-
neoplastic samples, and because the virus does cause
neoplasia, it seems likely that the virus isolated is the etio-
logical agent of molluscan hematopoietic neoplasia.

SQUID CATCHES ALONG THE UNITED STATES
CONTINENTAL SLOPE

W. F. RATHJEN

National Marine Fisheries Service
Gloucester, Massachusetts 01 930

During October-November 1979, the Federal Republic
of Germany research vessel ANTON DOHRN conducted a
trawl survey along the continental slope between Georges
Bank and Cape Canaveral (Florida). Primary depth coverage
ranged from 400 to 1,000 meters using commercial-size
otter trawls. Some limited coverage was accomplished on
the continental shelf.

Illex squid represented the largest volume of any one
species sampled during the cruise. These squid were
extremely cosmopolitan in their distribution with large
catches at both the most northerly and southerly locations
fished. The results experienced provide new information
on the ubiquitous distribution of Illex in the slope area
during the fall season. Hydrographic information was
recorded at each trawl station, and other biological observa-
tions were made on the size and maturity of the squids.

time of marking added 6.5 to 10 mm of new growth
in 294 days (x = 0.02 to 0.03 mm day" 1 ); and the largest
marked specimen (16.5 cm) added 2 mm of shell in 294
days (x~ = 0.01 mm day" 1 ).

Small mussels (N = 25; 8 to 27 mm long) also were
recovered from a slide box and bottle rack (N = 9) placed
at the rift vents for microbiological sampling. The slide box
and bottle rack were deployed for 294 days. If we assume
that the largest of these mussels represents an early primary
settlement of spat on the box and bottle, juvenile growth
rates are on the order of 0.09 mm day" 1 .

The growth data for file-marked mussels and juvenile
growth rates allow one to construct an ontogenetic growth
curve which predicts absolute age from shell length. Our
growth model indicates that the largest specimen collected
(16.7 cm) was 14 to 16 years old. Half of this maximum
length was obtained by the mussels in 3 to 4 years. The
modal age of the file-marked mussels ranged from 6 to 1 1
years.

The growth rates deduced for the Galapagos mussels
were among the highest growth rates documented for
deep-sea invertebrates. The ontogenetic growth curve for
Galapagos mussels is comparable to growth curves of
shallow-water mytilids.

STATISTICAL ANALYSIS OF DIGESTIVE GLAND TUBULE

VARIABILITY IN MERCENARIA MERCENARIA (L),

OSTREA EDULIS L., AND MYTILUS EDULIS L.

GROWTH OF MUSSELS AT DEEP-SEA HYDROTHERMAL
VENTS ALONG THE GALAPAGOS RIFT

DONALD C. RHOADS 1 ,
RICHARD A. LUTZ 2 AND
ROBERT M. CERRATO 1

Department of Geology and
Geophysics, Yale University,
New Haven, Connecticut 0651 1 , and

o

Department of Oyster Culture,
New Jersey Agricultural Experiment
Station, Rutgers University,
New Brunswick, New Jersey 08903

The deep-diving submersible ALVIN marked the posterior
shell margins of mussels with a file on February 12, 1979.
ALVIN returned to recover the marked mussels on Decem-
ber 3, 1979, after a period of 294 days.

New shell growth beyond the file mark was linearly
related to premark shell length (r > 0.95). The smallest
marked mussel (3.5 cm) added 17 mm of new shell in 294
days (x = 0.06 mm day" 1 ); specimens 12 cm long at the

W. E. ROBINSON

Marine Science Institute
Northeastern University
Nahant, Massachusetts 01908

Recent investigations indicate that marine bivalves
apparently demonstrate rhythms of intracellular digestion,
often correlated with the tidal cycle. Evidence is based
primarily, and often solely, on the diverse histological
appearances of the digestive gland tubules from different
individuals over a period of time. In general, four main
tubule types, signifying various stages of intracellular
digestion, can be recognized: I, holding; II, absorptive;
III, fragmenting; and IV, reconstituting. Digestive tubules
and similar tubule types are not distributed randomly within
the digestive gland, but are grouped together around
common secondary ducts. This necessitates the use of a
cluster sampling technique for proper statistical analysis.
In Mercenaria mercenaria, Ostrea edulis, and Mytilus edulis,
variability of tubule types is high within individual digestive
glands as well as between individuals sampled at the same
time. Based on calculations to minimize total variance, it

122 Abstracts, 1980 Annual Meeting, June 9-12, 1980

National Shellfisheries Association, Hyannis, Massachusetts

is better to sample a small area from numerous individuals
rather than a large area from a few animals. Intra-animal
variability is similar in all three species. Similarly, inter-
animal variability is the same in the subtidal quahog and
mid-intertidal mussel, but much less in the low intertidal
oyster. The problems imposed by variability and tubule
clustering have not been considered adequately in previous
investigations of bivalve digestion.

THE ECONOMICS OF ARTIFICIAL UPWELLING

MARICULTURE

OSWALD A. ROELS

Department of Marine Studies
The University of Texas
Port Aransas, Texas 78373

To determine the economics of artificial upwelling
mariculture, the clam Tapes japonica was grown over a
12-month period in the St. Croix system, operated in pilot-
plant fashion.

Seawater from a depth of 870 m was pumped continu-
ously into ponds (100 m 2 , 1 m deep) onshore. The ponds
were inoculated with the diatom Chaetoceros curvisetus
(STX 167) which was grown in continuous culture and
pumped to a Tapes japonica production line. The system
produced 81 kg of phytoplankton protein, and 423 kg
(whole wet weight) of clams in 12 months, corresponding
to a yield of 8.1 tons plant protein, and 42.3 tons of clams
per hectare per year.

An aquaculture budget generator was developed to
predict costs of artificial upwelling mariculture systems of
different sizes. Thus, for a plant producing 21 ,900 tons of
clams per year, the cost would be $0.77/kg of clams pro-
duced. The deep seawater costs represent $0.10 of that
total, the phytoplankton production $0.32, the shellfish
area costs $0.25, and supervisory costs represent $0.10.

The deep seawater system and the phytoplankton pro-
duction system are subject to considerable economies of
scale. The costs in the shellfish area do not vary much with
the capacity of the plant.

The economics of clam production obviously are most
sensitive to the phytoplankton cost.

'This work was supported by Sea Grant, National Oceanic and
Atmospheric Administration, and U. S. Department of Commerce.

SIZE AND AGE AT SEXUAL MATURITY OF OCEAN

QUAHOGS ARCTICA ISLANDICA LINNE, FROM

A DEEP OCEANIC SITE

JOHN W. ROPES AND
STEVEN A. MURAWSKI

National Marine Fisheries Service
Northeast Fisheries Center
Woods Hole, Massachusetts 02543

Gonadal tissues and the corresponding shells of ocean
quahogs Arctica islandica were collected during late July
to early August 1978, from off Long Island, New York, for
an examination of sexual development and growth line
formation. The collection dates were before the known
time of spawning for the species and when gonadal develop-
ment was expected to be in a ripe stage. Most of the clams
were of small size (x = 39.2 mm; standard deviation (SD) ±
8.13), ranging from 18.7 to 60.4 mm in shell length. A
5-year-old (41 .0 mm) and three 6-year-old (36.4 to 41 .0 mm)
clams were the youngest containing well developed gonads
and numerous sex cells, but a 10-year-old (47.9 mm) clam
only had moderately developed gonads containing few sex
cells. Gametogenesis indicative of the female sex was in
older (5-year-old) clams than in males (3-year-old), suggest-
ing a later attainment of sexual maturity of female clams.
Gonadal tubule development, gametogenesis, and attain-
ment of sexual maturity were variable with respect to size
and age.

SURVIVAL OF RECENT LARGE SOFT-SHELL CLAM SETS

IN HAMPTON-SEABROOK ESTUARY AND PROGRESS

TO HARVESTABLE SIZE

N. B. SAVAGE AND P. C. CLARK

Normandeau Associates Inc.
Bedford, New Hampshire 03102

Soft-shell clam population dynamics have been moni-
tored in Hampton-Seabrook Estuary for more than 9 con-
secutive years. By far the largest clam set was recorded in
1976, when an average of approximately 7 spat per ft
settled on five flats, totaling 165 acres.

Initially growth rate and survivorship were low, probably
because of crowding and predation. Sufficient numbers sur-
vived, however, to restore badly depleted harvestable stocks
to near historic levels. Rates of recruitment to harvestable
size were determined by following year-to-year changes
in size-frequency distributions. Recruitment rates, in turn,
were used to predict future standing-stock levels given
various management alternatives. Among the interesting
observations arising during the study were: (1) indications

National Shelltisheries Association, Hyannis, Massachusetts

Abstracts, 1980 Annual Meeting, June 9-12, 1980 123

that survivorship and growth rate improved with succeeding
year classes (1977 and 1978), and (2) coincidence of a six-
fold increase in abundance of sexually mature clams with
an eight-fold increase in midsummer abundance of soft-shell
clam larvae.

The present policy of restricting digging to 2 days per
week, September through May, appears to have helped the
stocks recover. However, the two largest and most produc-
tive flats probably could be opened to summer digging for
up to 2 years to the advantage of clam diggers and without
long-term adverse effects on the resource.

OYSTER SETTING-PAST, PRESENT, AND FUTURE

WILLIAM N. SHAW

National Sea Grant College Program
National Oceanic and Atmospheric
Administration
Rockville, Maryland 20852

Natural oyster sets are still essential if a viable oyster
industry is to continue in the United States. Although a
number of oyster hatcheries have been established, at best,
they can only supplement natural sets.

Many speculations have been made regarding the recent
causes of low setting rates, especially in the Chesapeake
Bay. Yet, no single cause can be found.

There is no question that the loss of brood stock from
MSX in the high-salinity waters of Virginia seriously affected
setting in the James River. Yet, setting has declined in
other Virginia rivers, the cause of which cannot be totally
related to brood stock losses from MSX.

In Maryland, MSX losses of any significance occurred
only in the southern part of the state. Major seed areas were
not in those areas. Still, especially during the past decade,
setting has been of low intensity.

Scientists in Japan have just completed extensive studies
related to oyster setting in Matsushima Bay. Number of
parent oysters, quantity of larvae produced, number of
seed collected, and efficiency of seed collecting were
determined. Based on those studies, new setting areas were
found and utilized. Those studies are described, and recom-
mendations are made that similar studies should be consid-
ered in the Chesapeake Bay.

POLYPLOIDY INDUCED IN THE EARLY EMBRYO OF
THE AMERICAN OYSTER WITH CYTOCHALASIN B*

JON G. STANLEY ' , STANDISH K.
ALLEN 1 AND HERBERT HIDU 2

Maine Cooperative Fishery Research
Unit, University of Maine, and

Ira C. Darling Center for Marine Studies
Walpole, Maine 04573

An attempt was made to induce polyploidy in the
American oyster by treating the zygote with cytochalasin B.
This antibiotic caused significant delay in the first cleavage
division, presumably without interfering with chromosome
replication. As a result, a significant number of larvae were
polyploid; 13 of 22 treated with 0.1 mg/1 cytochalasin, and
3 of 4 treated with 1 .0 mg/1. Survival at 24 hours was about
33% that of the controls for the larvae from the 0.1 mg/1
treatment, and 15% for larvae receiving 1.0 mg/1 cytochalasin.
Survival was greater for oysters treated for 15 minutes
beginning immediately after fertilization than if treatment
began later at 15 or 40 minutes. Oysters from the treated
zygotes set normally and subsequent survival was indistin-
guishable from those of controls. At 8 months, control and
treated oysters were 13 mm in length.

*Supported by grant 04-7 -158-44034, NOAA Office of Sea Grant.

USE OF AN OYSTER RACK FOR OFFBOTTOM

CONTAINERIZED-RELAYING OF POLLUTED

OYSTERS IN MISSISSIPPI SOUND

JOHN E. SUP AN AND
E. W. CAKE, JR.

Oyster Biology Section

Gulf Coast Research Laboratory

Ocean Springs, Mississippi 39564

An experimental oyster rack was used to relay 48 sacks
of naturally contaminated oysters into approved shellfish
growing waters south of Deer Island, MS, during two separate
trials. The 3.6 X 1.8 X 1.2 m rack (patent E. R. GoUott),
constructed primarily of welded angle iron, was designed to
hold 48, 86 X 56 X 10 cm, plastic chicken-coop bottoms
(polyethylene structural foam) in a sliding tray arrangement.
The trays were positioned in a 6-tray X 2-row X 4-level
arrangement, with a space of 5 cm between the four levels.
During the first experiment, oysters eliminated fecal coli-
forms from an initial median value of 1,400 MPN/100 gm
to a median of 45 MPN/100 gm after 7 days. A second
attempt produced a median value of 20 MPN/100 gm after
10 days, following an initial median value of 23,000 MPN/
100 gm. No attempt was made to acclimate oysters to the
higher salinities of the relaying waters. Mean condition

124 Abstracts, 1980 Annual Meeting, June 9- 12. 1980

National Shellfisheries Assocation, Hyannis, Massachusetts

indices increased by 2.5 gm/ml over the relaying period.
The mean oyster mortality was 1 .3%. The rack eliminates
the problems associated with onbottom relaying while
guaranteeing complete second harvests.

The findings of this preliminary study form a basis to
assess the appropriateness of the current harvesting season,
and the potential success of local seed transplant programs.

AN OVERVIEW OF THE SNOW CRAB (CHIONOECETES
OPILIO) FISHERY IN NEWFOUNDLAND

DAVID M.TAYLOR

Department of Fisheries and Oceans
St. John 's, Newfoundland
Canada A1C 5X1

The fishery for snow crabs (Oiionoecetes opilio) in
Newfoundland is comparatively new. Fishing began in 1969
with landings for that year of 90.7 X 10 3 kg. Landings have
risen dramatically in recent years peaking in 1979 at approxi-
mately 10.9 X 10 6 kg. A summary of annual landings for
Newfoundland since the fishery started is presented. Also
presented is a breakdown of annual catch-per-unit of effort
and total effort in management areas for which data are
available. Management policy and research projects along
with their objectives are discussed.

PRELIMINARY INVESTIGATIONS OF LOCAL POPULATIONS

OF THE BAY SCALLOP ARCOPECTEN IRRADEANS

LAMARCK IN FALMOUTH, MASSACHUSETTS

RODMAN E. TAYLOR

Woods Hole Oceanographic Institution
Woods Hole, Massachusetts 02543

In May 1979, a preliminary investigation of local popula-
tions of Argopecten irradians in Waquoit Bay. Falmouth.
Massachusetts, was begun. The specific problems investi-
gated in this preliminary program were: (1) migrations of
adult populations; (2) gonad development and time of
maturation and spawning of local populations; and (3)
growth of newly set juveniles during the harvesting season.

Movements of scallops were monitored at three stations
in the bay, and these movements appeared to be random
throughout the summer. Gonads of bay scallops were ripe
in May, and in a partially spawned condition during June
and July. Juveniles exhibited high growth rates throughout
the summer and fall; 90% of the individuals examined
reached a length of > 50 mm by the end of the year
(December 1979).

METHODOLOGY FOR SPECIFIC DIAGNOSIS OF CEPHALOPOD

REMAINS IN STOMACH CONTENTS OF PREDATORS WITH

REFERENCE TO THE BROADBILL SWORDFISH

XIPHIAS GLADIUS

RONALD B. TOLL AND
STEVEN C. HESS

Rosenstiel School of Marine and
Atmospheric Science
University of Miami
Miami, Florida 33149

The stomach contents from 65 broadbill swordfish,
Xiphias gladius, from the Straits of Florida were examined.
Previous studies have demonstrated the importance of
cephalopods in the diet of this predatory vertebrate, but
have omitted critical analyses of these remains. The majority
of the stomach contents encountered in the present study
were in extremely poor condition because of mechanical
and chemical breakdown incurred during ingestion and
digestion. Identification of remains became increasingly
difficult as the traditional sequence of character assess-
ment was interrupted by the deterioration and/or loss of
morphological and meristic characters.

Identifications were by necessity based on a synthesis of
less frequently utilized characters, inherently more resistant
to gastric breakdown. These included mantle musculature,
buccal membrane connectives, light organs, gladii, beaks,
spermatophores, and radulae. In addition, an examination
of viscera, when present, provided taxonomic information
as well as data concerning sex, state of maturity, and
fecundity.

Earlier studies based on sample sizes an order of magni-
tude greater than the present indicated a low diversity of
cephalopod species in the prey composition of X. gladius.
The utility of the approach outlined here is demonstrated
by the fact that 1 5 species representing 1 1 families in
two orders were encountered. The significance of this type
of analysis is further emphasized considering 1 1 of these
taxa have not been reported previously in the diet of
swordfish. In addition, one was a first record of occurrence
in the Atlantic, another was the largest known representative
of its family, and still another was the smallest recorded
mature male from the family Architeuthidae, the giant squids.

National Shellt'isheries Association, Hyannis, Massachusetts

Abstracts, 1980 Annual Meeting. June 9-12, 1980 125

PROTEIN DIGESTIBILITY IN THE LOBSTER
HOMARUS AMERICANUS

DONALD J. TRIDER AND
JOHN D. CASTELL

Department of Fisheries and Oceans
Fisheries and Environmental Sciences
Division, Resource Branch,
Disease and Nutrition Section
Halifax, Nova Scotia, Canada B3J 2S7

The digestibility of five different proteins (casein, whole
egg protein, soybean protein, shrimp protein concentrate,
cod fish protein concentrate) was determined in canner
lobsters (65 to 85 mm carapace length) using the chromic
oxide indicator method. No significant differences were
obtained in average total digestibility of the diets (60%),
but there were differences in protein digestibility. The
average percent apparent digestibility of the casein, whole
egg, and shrimp proteins was > 96%; soybean protein, 93%;
and cod fish protein, 85.5%. Factors contributing to differ-
ences in protein digestibilities, and problems encountered
doing digestibility studies with aquatic animals are discussed.

SEASONAL REPRODUCTIVE CYCLE AND SHOW

FACTOR VARIATION OF THE GEODUCK CLAM

PANOPE GENEROSA (GOULD) IN

BRITISH COLUMBIA

K. C.TURNER 1 AND
ROBERT K. COX 2

l 2S36 Mill Hill Road, and
Marine Resources Branch,
Ministry of Environment ,
Victoria, British Columbia 9B 4X7

Geoduck clams, Panope generosa (Gould), were collected
on a monthly basis from Cherry Point, Saanich Inlet, 35 km
north of Victoria, and gonads analyzed for reproductive
phase. Samples were harvested from May 1977 to August
1978, at a depth of 9 m.The reproductive cycle was divided
into five phases: early active, late active, ripe, partially
spent, and spent.

Four 100-m 2 plots were simultaneously observed to
determine what percentage of the population were visible
(siphons extended) at various times of the year, indicating
seasonal activity patterns. Plot populations were established.

Gametogenesis was observed first in September samples
and by early January, 98% of the clams were in the early
active phase. Six percent were ripe already. Most ripe speci-
mens occurred during April (5 4%) and May (91%). Spawning
began in May, and by June, 77% of the samples were

partially spent. All samples were in the spent phase by
August.

A total of 624 geoducks was collected during 1977 and
1978, from 52 locations; reproductive phases of these clams
were compared to those of the Cherry Point samples. No
significant variations were observed from the Cherry Point
cycle.

Siphon-show factor increased rapidly from February to
April and remained at a high, but reduced level during the
summer months. Shows decreased in the fall, and in January
monitoring, no animals were observed in any of the four
plots. A total of 1 ,1 75 animals were monitored.

ASPECTS OF LOLIGO PEALEl EARLY LIFE HISTORY

MICHAEL VECCHIONE

Virginia Institute of Marine Science
Tfie College of William and Mary
Gloucester Point, Virginia 23062

In the Middle Atlantic Bight off New Jersey and Virginia,
Loligo pealei was the most common squid species collected
in 2 years of zooplankton sampling. Planktonic L. pealei
were found in that area in spring, summer, and fall, and
there were no indications of multiple stocks. This species
was captured in waters with a salinity range of 31.5 to
34.0 ppt, and was confined to coastal waters except during
conditions when the Gulf Stream eddy resulted in strong
offshore surface transport. While highest abundances were
found in night surface samples, night subsurface collections
took larger specimens, indicating ontogenetic descent.
Tentacle length was correlated closely with dorsal mantle
length in preserved specimens of less than 7.5 mm dorsal
mantle length, indicating that tentacles are noncontractile
in newly hatched specimens.

LIMITATIONS AND POTENTIALS OF BAY SCALLOP

(ARGOPECTEN IRRADIANS) CULTURE IN

NEW ENGLAND

DENNIS WALSH

Aquaculture Research Corporation
Dennis, Massachusetts 02638

The Wampanoag Fisheries Project has completed a 3-year
aquacultural feasibility study to improve and stablize the
bay scallop population in Menemsha Pond, Gay Head,
Massachusetts. The potential of bay scallop culture in New
England was demonstrated by growth of hatchery-reared
seed during the summer and fall of 1978 in Menemsha Pond.

126 Abstracts, 1980 Annual Meeting, June 9-12, 1980

National Shellfisheries Association, Hyannis, Massachusetts

Two groups of hatchery seed averaging 3 to 4 mm in length
were planted in May— June, and reached a harvestable size
of 50 to 60 mm by November 1978. Seed that set naturally
in the pond in August averaged less than 10 mm in length
by November.

More important from an aquacultural point of view was
that the early seeding of Menemsha Pond resulted in
scallops exhibiting excellent growth characteristics (420 to
720 /i/day), and no spawning activity during the summer
months. Water temperatures were declining by the time the
scallops were big enough to develop gonads. Declining
water temperatures apparently favored a rapid increase in
the weight of the adductor muscle. This was evidenced by a
161% increase in the weight of the muscle of the 1977 year-
class during the period August— October 1978. Similar gains
were identified qualitatively in the 1978 year-class hatchery
seed.

A vertically integrated aquaculture business consisting
of a 10,000 square -foot hatchery, a seafood processing
facility, and a shellfish brokerage firm, coupled with a
fishermen's cooperative, was envisioned initially as a possible
means of stabilizing the unpredictable scallop harvest,
and of providing employment for the Wampanoag Tribe.
However, a careful evaluation of this entire proposal during
the third year of the program indicated that implementation
of this scallop aquacultural plant was not feasible at the
present time.

Problems facing scallop aquaculture in New England fall
into three major areas: (1) hatchery design and operational
time table, (2) field grow out of hatchery-produced seed,
and (3) harvest, sale and/or processing of the scallop crop.
Problems in hatchery design and operation include trans-
lating the current laboratory-scale culture of scallops into
a commercial production concept, and the development of
techniques for mass culturing of selected species of algae.
Problems in field grow out of hatchery-reared seed include
the logistical, legal, political, and economical ramifications
of using nursery techniques such as rafts, fenced-in areas, or
pumped raceways. Problems in the harvesting, selling.

and/or processing of the adult scallop include destruction
of scallop seed during harvesting of adults, difficulties in
establishing a single-product brokerage, and the high cost
of developing new seafood products that might utilize the
visceral portion of the scallop which presently is discarded.

SEASONAL VARIATIONS IN BODY COMPONENT INDICES
AND ENERGY STORES IN THE SEA SCALLOP
PLACOPECTEN MAGELLANICUS (GMELIN) '

W. E. WEHLING, W. E. ROBINSON
ANDM. P. MORSE

Marine Science Institute
Northeastern University
Nahant, Massachusetts 01908

Index values were determined on gonadal mass, digestive
gland, and the quick-and-catch components of the adductor
muscle in adult specimens of the sea scallop Placopecten
magellanicus collected at 6- to 8-week intervals over a 12-
month period. All tissue indices were found to vary signi-
ficantly over the year. Somatic tissues displayed a biphasic
annual pattern with highest values in late spring and fall,
and lowest values in midusmmer and midwinter. The
gonadal mass displayed a single annual peak in the summer
just prior to spawning. No significant sex-specific differences
were noted.

Energy stores were estimated by measuring total lipid
and glucose plus glycogen concentrations in the indexed
tissues. Concentrations of both storage types exhibited
seasonal patterns similar to those of the tissue indices.

The reciprocal nature of the gonadal mass and tissue
indices, and energy store concentrations in late spring and
summer suggests movement of energy stores from somatic
tissues to the gonad.

Research supported by Department of Energy Contract No. EE-
77-S-02-4580.

Journal o) Shellfish Research, Vol. 1, No. I, 127-133. 1981.

ABSTRACTS OF TECHNICAL PAPERS

Presented at 1 980 Annual Meeting

WEST COAST SECTION
NATIONAL SHELLFISHERIES ASSOCIATION

Tumwater, Washington
September 5-6, 1980

Tumwater, Washington, September 5-6, 1980 Abstracts, 1980 NSA West Coast Section Meeting 129

CONTENTS

Gregory J. Anderson and Kenneth K. Chew

Intertidal Culture of the Manila Clam Tapes japonica Using Hatchery-Reared Seed

Clams and Protective Net Enclosures 131

Flinn Curren

The Japanese Oyster Drill (Ocenebra inornatd) 131

James Donaldson

Hatchery Rearing of the Olympia Oyster Ostrea lurida 131

Jill E. Follett and Rober S. Grischkowsky

Investigation of Shell Disease in Alaska King and Tanner Crabs 132

Carolyn A . Foster

Cellular Response to Carmine in the Brown Shrimp Penaeus aztecus with Observations

on Virus-like Particles in the Heart 132

G. D. Heritage

Blue Mussel {Mytilus edulis) Culture in South Coastal British Columbia 132

Jack Lilja

Paralytic Shellfish Poisoning in Washington State, 1978- 1980 133

Scharleen Olsen

New Candidates with Aquaculture Potential in Washington State: Pinto Abalone
(Haliotis kamtscliatkatia), Weathervane Scallop (Pecten caurinus), and Purple-Hinge
Rock Scallop {Hinmtes multirugosus) 133

The following papers were presented at the September meeting but no abstract was available at time of printing.

/ H. Beattie

Selective Breeding of Pacific Oysters and the Summer Mortality of 1979

/. H. Beattie, B. Baldeson, L. Wiegardt and W. Breese

Eyed Larvae Transport-Is This the Way of the Future 9

G. Chislick

The British Columbia Oyster Industry-Long Line and Raft String Culture

Tumwater, Washington, September 5-6, 1980

Abstracts. 1980 NSA West Coast Section Meeting 131

INTERTIDAL CULTURE OF THE MANILA CLAM

TAPES JAPONIC A USING HATCHERY-REARED

SEED CLAMS AND PROTECTIVE

NET ENCLOSURES

GREGORY J. ANDERSON AND
KENNETH K. CHEW

College of Fisheries
University of Washington
Seattle, Washington 98195

Commercial feasibility of intertidally culturing the
Manila clam Tapes japonica was investigated at Filucy and
Wescott bays in Puget Sound, Washington. Hatchery-
produced seed clams were marked and planted at densities
of 1 ,000 clams/m 2 in areas protected by two layers of
12.5-mm mesh lightweight plastic netting. Unprotected
areas were seeded at densities of 900 clams/m 2 . Recovery
and growth of the marked clams were studied after 3,6,
and 12 months.

Recovery in protected areas (30 to 60%) was higher than
in unprotected areas (2 to 12%); this was attributed to
greater predation and washout in the unprotected areas.
Because of that, growth could be evaluated only for the
protected areas, in which mean shell lengths were similar
in both bays after 12 months. Clams were larger at lower
tidal heights; the growth rate appeared to decrease with
increasing tidal height.

At Filucy Bay, the average population density of large
(> 8 mm), wild Manila clams in the protected area increased
tenfold to 1 9 1 clams/m 2 ; the density of those wild clams in
the unprotected area decreased twofold to 16 clams/m 2 .
This suggests that the netting may act to concentrate
juvenile clams from the wild population as they are moved
about by wave activity. It is further speculated that the
density of larval settlement may be higher in the protected
area.

Net value of the potential harvestable biomass/m 2
suggests that this type of commercial culture operation is
both practical and economically feasible.

THE JAPANESE OYSTER DRILL (OCENEBRA INORNATA)

FLINN CURREN

College of Fisheries
University of Washington
Seattle, Washington 98195

The Japanese oyster drill Ocenebra inornate, introduced
on imported seed oysters, continues to be a problem in
certain areas on the western coast of the United States. In

the past, control has been attempted unsuccessfully by a
variety of methods such as the handpicking of aggregations,
tilling or discing infested grounds, draining pools to increase
dessication stress, chemical treatments, and physical and
chemical barriers. Pheromone-baited traps were suggested
as a potential control technique during the spring and fall
periods of snail aggregations. A study started in June 1980,
is attempting to prove the existence of aggregation
pheromones, determine the sites of pheromone production,
and extract and concentrate chemicals acting as attractants
for the Japanese oyster drills. Future studies should include
isolation, identification and synthesis of pheromones, and
development of pheromone-baited traps.

HATCHERY REARING OF THE OLYMPIA OYSTER
OSTREA LURID A

JAMES DONALDSON

Coast Oyster Company
Quilcene, Washington 98376

The Olympia oyster industry was once a thriving industry
on the western coast of North America and especially in
the state of Washington. It began simply as a fishery on
existing natural stocks and, eventually, developed into an
intensive culture operation. Depleted populations, lack of
recruitment, the Japanese oyster drill, and the flatworm
have had a role in the decline of the now decimated popula-
tions. Hatchery-grown seed is the only apparent method to
restore beds to production levels.

Hatchery techniques are described for rearing this
species from the brooding larval phase through to setting
size. Three groups of brood stock in different quantities
were maintained in a closed system at different times of
the year to determine the desirable number of adults needed
for hatchery production. About 1 million larvae were
obtained from a brood-stock size of 50 oysters from June 12
through August 9; 104 million larvae were obtained from
5.000 oysters kept in the hatchery from December 6
through February 8; and 23 million were liberated from a
group of 1 .000 oysters from March 12 through April 22.

Larval-rearing techniques are described which resulted in
growth periods of 15 to 23 days from liberation to setting.
Setting was successful; however, a high mortality occurred
in the first 2 weeks after setting for all groups.

132 Abstracts, 1980 NSA West Coast Section Meeting

Tumwater, Washington, September 5-6, 1980

INVESTIGATION OF SHELL DISEASE IN ALASKA
KING AND TANNER CRABS

JILL E. FOLLETT AND
ROGER S. GRISCHKOWSKY

Alaska Department of Fish and Game
Fish Pathology Section
Anchorage, Alaska 99502

The commercial crab industry in Alaska has experienced
problems due to the poor condition of both the king crab
Paralithodes camtschatica, and the tanner crab Chionoecetes
bairdi. These problems include low meat yield, low vigor,
soft shell, inability to molt, and the presence of dark
lesions which pit the exoskeleton. Bacterial and histological
studies were initiated to find solutions to these problems.
Preliminary studies indicated no difference in numbers of
types of bacteria present in normal or diseased crabs.
Pseudomonads, aeromonads, and myxobacteria were
isolated most commonly. Chitinoclastic bacteria seldom
were isolated although the exoskeletons were pitted by
lesions. No one organism was associated with the lesions.
Through these, bacteria were able to gain entrance to the
interior of the crab. Blood or lymph could become infected
easily through the lesions.

Rapid death of tanner crabs ensued following injection
of either of two common isolates. The isolates were a
Moraxella sp. and a Pseudonumas sp.,most closely related to
Pseudomonas stutzeri. Infection of healthy crabs and
repeated recovery fromdiseased ones indicatedpathogenicity
although some crabs survived infection and some were able
to eliminate the bacteria. The susceptibility of a particular
crab probably related to its overall health. Additional studies
may reveal mechanisms of transmission, distribution of
pathogenic bacteria in host tissue, and management strategies
to minimize future loss.

CELLULAR RESPONSE TO CARMINE IN THE BROWN

SHRIMP PENAEUS AZTECUS WITH OBSERVATIONS

ON VIRUS-LIKE PARTICLES IN THE HEART

role in such reactions, but noncirculating cells in the heart,
gills, and hepatopancreas also participate in the surveillance
and clearance of foreign substances. The purpose of the
present study was to examine by transmission electron
microscopy the clearance of carmine particles in the gills
and heart of the brown shrimp Penaeus aztecus to demon-
strate the phagocytic capabilities, functional relationships,
and ultrastructural characteristics of circulating and non-
circulating phagocytic cells. During this study, virus-like
particles were observed within cardiac cells and their
significance is discussed.

A 1 .4% carmine-saline solution was injected into the
sternal sinus, and the shrimp were sacrificed for light and
electron microscopy at intervals up to 8 days postinjection.
Within 1 hour carmine particles were clumped in the
hemolymph and phagocytized or encapsulated by neuro-
cytes. Hyalinocytes and semi-granulated hemocytes were
more phagocytic than mature granulocytes. No carmine
was observed in the gill podocytes, but their large dense
vacuoles appeared to increase in size and number. Podocytes
share structural characteristics with cells of the vertebrate
renal glomerulus and probably aid in clearing the hemo-
lymph of fine particulate material. Fixed phagocytes in the
heart were attached loosely to the basal lamina surrounding
myocardial cells and were weakly phagocytic for carmine
particles, wlrich accumulated in a large cytoplasmic vacuole
containing cellular debris and dense flocculent material.

Viral inclusions were observed in the characteristic
vacuole of fixed phagocytes in the heart. Inclusions
measured ca. 1 /im in diameter, and often were surrounded
partially by a membrane. Each consisted of a tightly packed
aggregate of small, nonenveloped, osmiophilic particles
ca. 23 nm in diameter. Some of the particles appeared to be
square-shaped, and many were organized in linear arrays.
If the particles are an eucaryotic virus, they may belong to
either the parvovirus or the picomavirus group. However,
the virions may be phages infecting a phagocytized
prokaryote whose cell wall and/or membrane were partially
digested.

CAROLYN A. FOSTER

College of Fisheries
University of Washington
Seattle, Washington 98195

Crustaceans generally combat infection by recognizing
and clearing the hemolymph of 'nonself.' Although humoral
factors act synergistically with cellular defense mechanisms,
the latter are the principle means of internal defense and
include coagulation, phagocytosis, and encapsulation. In
penaeid shrimp, circulating hemocytes play an important

BLUE MUSSEL (MYTILUS EDVLIS) CULTURE IN
SOUTH COASTAL BRITISH COLUMBIA

G. D. HERITAGE

Department of Fisheries and Oceans
Pacific Biological Station
Nanaimo. British Columbia
Canada \9R SK6

A project to investigate the commercial feasibility of
blue mussel (Mytilus edulis) culture in British Columbia was

Tumwater. Washington, September 5 -6, 1980

Abstracts, 1980 NSA West Coast Section Meeting 133

begun in 1979 at eight locations. Biological parameters
investigated were growth, mortalities, fouling, predation,
and recruitment.

Surveys of wild mussel beds showed that stocks of seed
mussels suitable for culture in Netlon socks were plentiful
only at a few locations in the Strait of Georgia but were
common on the western coast of Vancouver Island. Wild
mussels from the intertidal zone that were placed in Netlon
socks and suspended from rafts grew to approximately
50 mm shell length in 12 months after suspension. Severe
unexplained mortalities were experienced at all sites.

Fouling by barnacles {Balanus glandulus) was heavy at
most sites; fouling by hydroids, bryozoans, algae, and
anemones was common.

Heavy predation by ducks, Barrow s goldeneye (Bucephala
islandica), and by surf scooters {Melanitta perspicillata) was
experienced at all sites during the winter months. Starfish
(Pisaster ochraceus) destroyed mussel seed at one site, and
pile perch (Rhacochilus vacca) were observed feeding on
small mussels at another.

Suspended ropes successfully collected commercial
quantities of seed at seven sites in both 1979 and 1980.
Seed collected in the summer of 1979 grew to market size
(50 mm shell length) in 10 to 12 months at some locations
but again heavy unexplained mortalities were experienced
in 1980.

The problems of heavy mortalities and predation must
be overcome if commercial mussel culture is to become
feasible in British Columbia. Some mechanization also is
required for processing mussels in areas of heavy fouling.

At present there are six mussel culture pilot projects
(including the one described here) underway in British
Columbia, and seven lease applications for mussel culture
are pending.

PARALYTIC SHELLFISH POISONING IN
WASHINGTON STATE, 1978-1980

JACK LILJA

Advisory Sanitarian, Shellfish Program
Department of Social and Health Services
Olympia. Washington 98501

During the past 10 years (1970—1980), there has been a
dramatic increase in the paralytic shellfish poisoning samp-
ling program in Washington State. Samples processed for
PSP toxin have increased from 100 in 1970 to 1 ,200 in 1980.
Factors contributing to the increased sampling include:
(1) movement of the causative agent to previously unaffected
areas, (2) increased public awareness and interest in the
problem, and (3) paralytic shellfish poisoning research
projects. Sampling locations have been expanded to cover
nearly all shellfish growing areas in Puget Sound. An
extensive dinoflagellate bloom occurred in late summer of
1978, and it affected a large area in central Puget Sound,

primarily sport shellfish beaches. Sport shellfish samples
have increased from 16% of total samples in 1970, to 60%
of total samples in 1980. Butter clams from areas that have
been affected for a number of years remain toxic year
around, but butter clams from newly affected areas lose
their toxicity during the winter months. Further informa-
tion on uptake and release of toxin by various shellfish
species is being examined.

NEW CANDIDATES WITH AQUACULTURE POTENTIAL IN

WASHINGTON STATE: PINTO ABALONE (HALIOTIS

KAMTSCHA TKANA), WEATHERVANE SCALLOP

(PECTEN CAURINUS), AND PURPLE-HINGE

ROCK SCALLOP (H1NNITES

MULTIRUGOSUS)

SCHARLEEN OLSEN

Washington Department of Fisheries
Point Whitney Shellfish Laboratory
Brinnon. Washington 98320

Three under-utilized native species are being investigated
for their commercial aquaculture and enhancement potential.
These aquaculture candidates include the pinto abalone
(Haliotis kamtschatkana), and two scallop species: the
weathervane (Pecten caurinus) and the purple-hinge rock
scallop (Hinnites multirugosus).

An experimental minihatchery facility has been estab-
lished at the Point Whitney Shellfish Laboratory, Brinnon,
WA, and progress has been made in culturing the larvae of
all three species. The pinto abalone have spawned consis-
tently when exposed to 10~ 6 m concentration of hydrogen
peroxide buffered with tris(hydroxymethyl)aminomethane
to pH = 9. Adult abalone have been conditioned for over a
year in the laboratory, and spawnings have occurred success-
fully each month from March through November. Meta-
morphosis was stimulated with gamma aminobuteric acid
on day 9 after spawning. Juvenile abalone were grown to
25 mm in 14 months in unfiltered seawater at ambient
temperatures (8.5 to 14.0°C).

Spontaneous spawnings in May for the weathervane
scallops, and in May and September for the purple-hinge
rock scallop provided viable larvae for study, although all
attempts to stimulate spawnings have been unsuccessful.
Larvae of each species were cultured to metamorphosis in
34 to 40 days at which time high mortality occurred. Larval
scallops were grown in seawater filtered to 10 /mi at
temperatures of 9 to 16°C in static culture, and fed a
mixture of Monochrysis sp., Isochrysis sp., and Psuedo-
isochrysis sp. at concentrations of 10,000 to 50.000 cells/ml.

Further investigations of scallop spawning techniques
and methods, as well as larval culture and grow-out methods,
will be conducted in future studies.

a

JOURNAL OF SHELLFISH RESEARCH

VOLUME 1, NUMBER 2

DECEMBER 1981

The Journal of Shellfish Research (formerly Proceedings of the

National Shell fisheries Association) is the official publication

of the National Shellfisheries Association

Editor

Dr. Robert E. Hillman

Battelle

New England Marine Research Laboratory

Duxbury, Massachusetts 02332

Assistant Editor

Dr. Edwin W. Cake, Jr.
Gulf Coast Research Laboratory
Ocean Springs, Mississippi 39564

Associate Editors

Dr. Jay D. Andrews

Virginia Institute of Marine Sciences

Gloucester Point, Virginia 23062

Dr. Anthony Calabrese
National Marine Fisheries Service
Milford, Connecticut 06460

Cornell University
Ithaca, New York 14853

Dr. Richard A. Lutz
Nelson Biological Laboratories
Rutgers University
Piscataway, New Jersey 08854

Dr. Kenneth K. Chew
College of Fisheries
University of Washington
Seattle, Washington 98195

Dr. Gilbert Pauley
College of Fisheries
University of Washington
Seattle, Washington 98195

Dr. Paul A. Haefner, Jr.
Rochester Institute of Technology
Rochester, New York 14623

Dr. Daniel B. Quayle
Pacific Biological Laboratory
Nanaimo, British Columbia, Canada

Dr. Herbert Hidu
Ira C. Darling Center
University of Maine
Walpole, Maine 04573

Dr. Louis Leibovitz

New York State College of Veterinary Medicine

Dr. Aaron Rosenfield

National Marine Fisheries Service

Oxford, Maryland 21654

Dr. Frederic M. Serchuk
National Marine Fisheries Service
Woods Hole, Massachusetts 02543

Journal of Shellfish Research

Volume 1. Number 2

December 1981

Journal of Shellfish Research, Vol. 1, No. 2, 135, 1981.

SPECIAL SQUID SYMPOSIUM

Presented at
ANNUAL MEETING OF THE NA TIONAL SHELLFISHERIES ASSOCIA TION

Hyannis, Massachusetts
June 8-12, 1980

INTRODUCTION

TERENCE W. ROWELL

Fisheries and Oceans Canada

Resource Branch

Halifax, Nova Scotia, Canada B3J 2S7

Cephalopods represent a major fishery resource widely
distributed throughout the oceans of the world. Of the
several hundred species harvested, squids of the families
Loliginidae (Loligo opalescens, L. pealei, L. plei), and
Ommastrephidae (Illex illecebrosus) are important to North
American fisheries.

Expansion of world squid fisheries in recent years has
led to a rapid increase in the exploitation of North American
stocks. Japan, as the world's foremost harvester and con-
sumer of squid, has led in this expansion, although the
Soviet Union and a number of other countries have also
directed considerable effort toward increased harvest of
the resource.

The fishery for short-finned squid, /. illecebrosus, on
the Atlantic coast of Canada illustrates this expansion,
showing a rapid increase from an annual average catch of
about 4,500 metric tons (MT) during the 1970-74 period
to roughly 153,000 MT in 1979. This huge increase in
landings, by both foreign and domestic fishermen, has
quickly brought the biological and management problems
into focus, and has stimuated a number of new research
initiatives on the part of both governmental and nongovern-
mental research institutions.

The current interest in squid as a major fishery resource
has provided what must be one of the most exciting and
biologically challenging areas for fisheries research and
management. The scope of problems involved are again
illustrated by Illex, with its short life span (generally
estimated at 12 to 18 months); its unknown spawning
distribution; poorly known distribution of larval, juvenile,
and adult stages; unknown migration patterns;and unknown

stock relationships. Unlike most finfish, where a number
of year-classes may be monitored for several years prior
to recruitment to the fishery, and where predictive popu-
lation assessments can be used to establish harvest levels,
an Illex year-class is first seen in the same year as the
fishery; there is no possibility of applying currently avail-
able assessment and predictive models to determine optimal
harvest levels.

It was in consideration of the commercial importance
and the challenging biological problems presented by our
North American squid resources that the National Shellfish-
eries Association asked that I organize a Special Session on
Squid for its 1980 Annual Meeting in Hyannis, Massachusetts.

For that Special Session, contributed papers were
requested to focus on one of three topic areas: (1) on the
historical overview and description of the fisheries; (2) on
biological and ecological studies important to understanding
the resource and its management; and (3) on population
biology, modeling, and prediction as applicable to squids. A
total of twelve papers were presented at the Special Session;
nine are being published in this dedicated issue. Abstracts
of all the papers appeared in Volume 1 , Number 1 of the
Journal of Shellfish Research. These papers provide new
information on adult and larval distribution, growth and
feeding and geographically related growth variances, and
recognition of cephalopod species and species groups in
predator stomach contents. Information is also provided
on the current status of the squid fisheries of eastern
North America, yield-per-recruit analysis for the two most
important east coast species, L. pealei and /. illecebrosus,
and on abundance forecasting and aging of/, illecebrosus.

135

Journal of Shellfish Research, Vol I. No. 2, 1.17 142, 1981.

DEVELOPMENT OF THE NEWFOUNDLAND SQUID (1LLEX 1LLECEBROSUS)
FISHERY AND MANAGEMENT OF THE RESOURCE

EARLG.DAWE

Department of Fisheries and Oceans,
Research and Resource Services
P.O. Box 5667, St. John's, Newfoundland,
Canada A 1C 5X1

ABSTRACT The Newfoundland short-finned squid fishery has traditionally been prosecuted inshore using small boats
and jigging devices. Catches from that fishery have historically been small because of limited markets. Recently, with the
development of new markets, that fishery has experienced unprecedented success and catch level has increased dramatically
since 1974.

The life history of Illex illeccbrosus is outlined herein, and the development and management of the Newfoundland
squid fishery are reviewed. Prospects for further expansion of that fishery are considered to be closely related to market
conditions. Development of new markets and increasing access to existing markets will depend on the success of other
worldwide squid fisheries and the quality of Canadian squid exports.

INTRODUCTION

BASIC LIFE HISTORY

The short-finned squid has long supported a small inshore
fishery at Newfoundland (Squires 1057, Mercer 1973a,
Hurley l l »80a). A seasonal migrant to the Newfoundland
fishing area (Northwest Atlantic Fisheries Organization
[NAFO] Subarea 3), Illex illeccbrosus is fished between
July and November using small open boats and jigging
devices (Quigley 1964, Mercer 1970, Voss 1973, Rathjen
et al. 1979, Hurley 1980a). Until recently yearly catch
levels have usually been less than 1 1,000 metric tons (MT)
(Mercer 1973a), primarily because of the unavailability of
substantial markets for squid resources in general.

New markets, however, have developed for squid as food
for human consumption. In response to increasing foreign
demand for seafoods and dwindling traditional resources,
attention has focused on exploitation of previously under-
utilized species (Rathjen 1977). Further, a worldwide trend
in recent years toward claiming national jurisdiction over
coastal fishing zones has led to attrition of far-seas fisheries
traditionally prosecuted by some major squid-consuming
nations (Hurley 1980a). Coincidentally with evolution of
foreign markets for cephalopod resources, yearly catch
levels in the Newfoundland squid fishery have risen (Beck
et al. 1980, Hurley 1980a). With the rise in level of exploita-
tion comes the need for sound management strategies
regarding conservation and determining levels of optimum
exploitation.

The basic life history of/, illeccbrosus is outlined herein
and the Newfoundland squid fishery is described. Historic
and recent trends in catch and inshore abundance are dis-
cussed, and current management strategies are described.
Also, the present status of this fishery is assessed in relation
to perspectives for its further development.

The life history of Illex illecebrosus is not completely
understood, because concentrations of spawning adults
and egg masses have not been encountered. Spawning is
believed to take place during January-February within the
influence of the Gulf Stream. Larvae and juveniles of less
than 5.0 cm in mantle length have been found during
February and March research cruises in 1979 (Fedulov and
Froerman 1980) and in 1981 (Dawe et al. 1981 ). Occurrence
of those early stages is temperature related. Fedulov and
Froerman (1980) found the major center of early-stage
distribution during March-April 1979 to be within the slope
water mix, near the northern boundary of the Gulf Stream.
Greatest catches occurred when temperature at fishing depth
ranged from 14.3 to 16.3°C (Fedulov and Froerman 1980).

In May-June, squid have historically been found on the
Grand Bank where their occurrence was also temperature
related. Greatest catches usually occurred where bottom
temperatures exceeded 5.0°C (Mercer and Paulmier 1974,
Hurley 1980b). Squid generally range from 9.0 to 18.0 cm
in mantle length at that time (Squires 1957, Mercer and
Paulmier 1974). Since 1974, incidental catches of squid
on the Grand Bank during May-June groundfish surveys
have provided an indication of later inshore abundance
(Squires 1957, 1959; Hodder 1964; Mercer 1973b; Hurley
1980b).

During the summer short-finned squid are distributed
between Hamilton Inlet and Cape Hatteras (Squires 1957,
Templeman 1966). However, fishable concentrations usually
occur between northern Newfoundland and Cape Cod.
Squid are fished by bottom trawl off the coast of the United
States and on the Nova Scotian Shelf. In Newfoundland,
they usually move inshore in July, although timing of

137

138

Dawe

inshore migration varies yearly, and between July and
November they support a fishery on the northeastern and
southern coasts of Newfoundland. They usually move
offshore again in November when most fall within the 20-
to 28-cm range in mantle length (Squires 1957, Mercer
1975, Collins and Ennis 1978, Hurley et al. 1979, Beck et al.
1980). Females leave the inshore area later than males and
show little sign of sexual maturation by the time they
migrate. Males are smaller than females and many have
reached advanced stages of maturity at migration (Squires
1957, Mercer 1973c, Collins and Ennis 1978, Hurley et al.
1979, Beck et al. 1980).

The fate of post-spawning adults is still largely a matter
of conjecture, because a reliable method of aging this squid
is not yet available (Hurley and Beck 1979a). However,
from laboratory research (Durward et al. 1 980) and examina-
tion of length-frequency distributions, it is believed they
live approximately 1 year and die after spawning. Thus,
each year the fishery would be entirely dependent on the
recruiting year-class.

THE NEWFOUNDLAND SQUID FISHERY

Trends in Catch and Inshore Abundance

Historical trends in inshore nominal catch of short-
finned squid at Newfoundland and corresponding qualitative
estimates of annual inshore abundance are presented in
Figure 1. A general feature of squid abundance is that it is

subject to severe year-to-year fluctuations with no regular
or predictable cyclic nature. However, years of very high
squid abundance are more common than scare or very
scare years. Fluctuations in year-to-year inshore abundance
may reflect fluctuations in actual population abundance or
yearly variations in that portion of the population which
becomes available to the inshore fishery. Hydrographic and
feeding conditions on the Grand Bank have been cited as
possible factors affecting yearly variations in the extent of
inshore migration (Ennis 1978). Irregular year-to-year
fluctuations in abundance are to be expected in such a
short-lived species, since recruitment would be highly
dependent on environmental perturbations.

Until recently, trends in annual catch have been similar
to yearly fluctuations in abundance (Figure 1). However,
the increasing magnitude of those catches reflect develop-
mental stages of the fishery. Until about 1950, catches were
small because the only major market for Illex illecebrosus
was dried squid for foreign markets, mainly China. In the
early 1950's, catches increased as a market developed to
supply bait to European interests fishing in the northwestern
Atlantic. Fishing technology improved considerably in 1965
with the introduction of the Japanese mechanized jigger
(Quigley 1964). Using that device fishermen experienced
much greater catch rates than they had previously using a
single lead jigger.

In the mid-1970's, a market for squid as food for human
consumption developed, mainly in Japan and in European

i ' ' " i '

T T TT "
10

2 9

VERY
ABUNDANT

VERT
SCARCE

i-i — am 1 1 ii |

| DRIED SQUID EXPORTS

□ FROZEN SQUID EXPORTS

□ FRESH AND FROZEN SQUID FOR BAIT

Jm

«Mw

100
90 2
80 J,
70-

vt

60g
u

50 £

UJ

a
40^

O

30 |
20 |

10

1980

Figure 1. Qualitative estimates of inshore abundance of squid at Newfoundland, 1879-1980, and breakdown of inshore catch, 1911-1980,
into processing categories. Data sources include Templeman (1966), ICNAF (1978), NAFO (1980), and unpublished data provided by the
Economics and Intelligence Branch, Department of Fisheries and Oceans. (Note change in scale of the ordinate in describing catch for the
period 1976-1980.)

Newfoundland Squid fishery and management

139

countries. As a result, and with consistently high levels of
inshore abundance, Newfoundland inshore nominal catch
increased steadily to a record high of 83,000 MT in 1979
(Figure 1). Other factors which contributed to such high
catch levels included the rejuvenation of the squid-drying
industry in 1978, and the development of a large interna-
tional fishery in Canadian waters. The offshore squid fishery
is prosecuted mainly on the Nova Scotian Shelf; however,
since 1970, small offshore catches have occurred in NAFO
Subarea 3 as well (Figure 2). Offshore Subarea 3 catch
remained less than 40 MT until 1975. Yearly catch increased
steadily until 1978 when approximately 5,700 MT, repre-
senting 14% of the Subarea 3 total catch, were taken by
the international fleet. Since that time the offshore catch
in Subarea 3 has declined with less than 1 MT caught in
1980 (Figure 2). An increase in inshore processing facilities
has further contributed to recent expansion of the New-
foundland fishery (Hurley 1980a).

1970 71

Figure 2. Trends in offshore Subarea 3 catch of short-finned squid,
1970-1980. Data sources include the FLASH information system,
ICNAF Redbook (1978), NAFO Scientific Council Report (1979-
1980), and unpublished data provided by the Economics and
Intelligence Branch, Department of Fisheries and Oceans.

Despite continued abundance of squid in 1980, the New-
foundland inshore catch (32,000 MT) dropped considerably
below the level of the previous year (Figure 1 ). That was pri-
marily because of poor market conditions for /. illecebrosus
which resulted in low prices offered to fishermen and a
reduction of effort in the inshore fishery. A dispute between
fishermen and processors during the summer of 1980
resulted in a further reduction in fishing effort. Production

of dried squid decreased also because of declining prices
and availability of the resource, as well as poor weather
conditions during the summer.

Management of the Resource

The short-finned squid fishery in Canadian Atlantic
waters is managed internationally by the NAFO, formerly
the International Commission for Northwest Atlantic
Fisheries (ICNAF). Prior to 1975, regulation of the fishery
was not restrictive because exploitation was light. Usually
yearly catch levels did not exceed 1 1 ,000 MT, the only
major fishery being prosecuted inshore at Newfoundland.
With increasing foreign catches on the Nova Scotian Shelf
in the 1970's, catch regulation was first implemented in
1975. Because of the unpredictable nature of fluctuations
in abundance or availability of the resource, a conservative
approach was taken in allocating catch quotas. Between
1975 and 1977, an open-ended yearly total allowable catch
(TAC) of 25,000 MT was determined with 15,000 MT
allocated to the USSR and 10,000 MT reserved for the
Canadian domestic fishery. In addition, all other partici-
pating countries without specific allocations were allowed
3,000 MT each (NAFO 1980).

International involvement in the offshore trawl fishery
increased dramatically over the 1975—1977 period. With
continued abundance of squid and no specific restrictions
in the Newfoundland inshore fishery, total catch for
Subareas 3 and 4 reached a high of 80,000 MT in 1977
(ICNAF 1979). In 1978, it was felt that during those years
of high squid abundance the existing level of TAC was
restrictive and resulted in losses of potential yield (ICNAF
1978). Thus, in 1978, a TAC of 100,000 MT was set,
assuming the 1978 squid abundance would be similar
to that of the previous year. As a means of avoiding over-
exploitation, should abundance be lower in 1978, effort
regulation was also introduced (ICNAF 1978). Catch rates
from the 1977 international fishery were applied to the
1978 TAC to ensure that the exploitation rate would remain
constant even if squid abundance decreased.

In recent years, abundance has remained high and post-
season estimates of population size (Hurley and Beck 1979b,
Dawe and Beck 1980) have consistently indicated that the
exploitation rate and the TAC could be increased the
following year without serious risk of over-exploitation
(NAFO 1980). Thus, the level of the TAC for Subareas 2,
3, and 4 has risen to 1 20,000 MT in 1979, and to 150,000 MT
in 1980 (NAFO 1980). Effort regulation in the international
offshore fishery has been maintained, based on 1978 catch
rates, as a safeguard against over-exploitation in years of
low squid abundance.

Other management initiatives included the introduction
of a June 15-opening date for the offshore fishery in 1978
(ICNAF 1978). That restriction was based on the fact that
by-catch of other species in the offshore fishery was high
early in the season and market value of squid was low

140

DAWE

because of their small size. In 1979, the commencement
date of the fishery was advanced to July 1 (ICNAF 1979).

Specific regulations have not been applied to the New-
foundland inshore squid fishery because it was felt that
high catches from that fishery were not likely to cause over-
exploitation of the resource. The inshore fishery focuses
on only a portion of the stock, the offshore component
being regulated by catch-and-effort restrictions. Thus,
restrictions in the offshore fishery provide for sufficient
spawning escapement should the inshore portion be heavily
exploited. Moreover, over-exploitation is less likely inshore
because the fishery is passive and does not seek out concen-
trations of squid in years of low abundance, as is possible in
the offshore fishery (NAFO 1980). In years of low abun-
dance the inshore fishery would likely fail and fishing
mortality would remain fairly constant because squid would
not be available to jigging devices.

CONSIDERATIONS IN MARKETING SHORT-FINNED SQUID

Newfoundland inshore squid production has increased
dramatically in recent years in response to the development
of new markets. However, international competition for
market access is intensive. In 1 977, world cuttlefish and squid
production reached almost 1 x 10 6 MT with Todarodes
pacificus and Illex illecebrosus, respectively, being the most
important species (Ramalingam 1978). However, world
cephalopod resources are still underexploited and annual
potential production could be 90 to 600 x 10 6 MT(Ampola
1974, Rathjen et al 1977, Voss 1973). With recent develop-
ments in technology for harvesting squids (Kato 1970;
Rathjen 1973, 1977; Voss 1973) and availability of squid
resources to many countries (Ramalingam 1978), world
production is limited primarily by market demand.

The most extensive markets for squid exist in Japan and
southern Europe. Japan is by far the greatest squid consum-
ing and importing nation. In the 1970's, the Japanese
market developed largely as a result of increased Japanese
demand for seafood, loss of foreign squid fisheries, and
recent decline in the domestic Japanese fishery for T.
pacificus. During the 1960's, Japanese domestic catch
averaged approximately 600,000 MT yearly (Voss 1973).
However, yearly catch levels declined during the 1970's,
with total landings of squid and cuttlefish being 480,000 MT
in 1979. As a result of decreased domestic production,
squid and cephalopod imports into Japan have increased
during the 1970's, from an estimated 37,000 MT in 1973
(Ramalingam 1978) to 156,000 MT in 1979. The regulation
of cuttlefish and squid imports into Japan is through
import quotas set twice yearly for unprocessed products.

Gaining access to that market is difficult because more
than 30 exporting nations compete for a share of the
inport quotas. Problems in marketing /. illecebrosus include
the belief that T. pacificus and Loligo spp. are preferred
as raw material. Short-finned squid is further processed in
Japan and that species is not well suited to the Japanese

processing system (Court 1980). Markets other than Japan
exist mainly in southern Europe. The most important of
those smaller squid-importing countries include Spain,
Portugal, Italy, France, and Greece. Outside Japan, markets
for dried squid exist in Hong Kong and Taiwan. Although
each of those markets is small compared to Japan, their
combined potential for absorbing squid and squid products
is considerable.

The importance of Canadian short-finned squid (/.
illecebrosus) as a Japanese import has increased considerably
during recent years to the point where, in 1979, Canada
supplied 15,483 MT which represented 10% of total imports
by Japan. Although Japan imported only 83,991 MT of
cuttlefish and squid in 1980, Canada supplied 18,409 MT
(22%), mostly 1979 production, and was the largest supplier
of squid to Japan.

That increased market access for Canadian squid (/.
illecebrosus) may reflect Japan's recognition of Canada as
a stable source of future squid imports. Also, through
developmental charters with Canada, Japan landed high
quantities of short-finned squid in 1978 and 1979. That
and a considerable increase in direct allocations to Japan
in 1980 were considered to be important steps toward
increasing Canadian access to the Japanese market. Despite
relative success in marketing Canadian short-finned squid
in 1980, markets were poor, which was reflected in a
decline in catch below that of the previous year. The sharp
decline in the inshore Newfoundland catch (Figure 1) was
due to a reduction of fishing effort which partly resulted
from a reduction in the price paid to fishermen. The
domestic Japanese inshore fishery for T. pacificus experi-
enced unprecedented success in 1980, resulting in a total
Japanese catch of squid and cuttlefish of approximately
600,000 MT. Consequently, there were no Japanese import
requirements and Canadian processors were offered low
prices for squid. That price was ultimately reflected in the
price offered to fishermen, approximately half that of the
previous year. Also, because of the self-sufficiency of the
Japanese market, no import quota was announced until
November, and Canadian processors were reluctant to
purchase squid with no firm purchase commitments from
Japanese interests.

At least in the short term, the success of the Newfound-
land inshore fishery and the Canadian fishery, in general,
will depend on resource abundance and market demand.
Canadian catches will probably fluctuate yearly depending
on success of other squid fisheries, especially by Japan, and
on the extent of import requirements by squid-consuming
nations.

To increase access to existing and future markets, the
status of /. illecebrosus as a desired import must be main-
tained. Measures should be taken to maintain and improve
the quality of the product. Grading of both dried and
frozen squid would render those products more attractive
to Japanese interests for further processing. Reliable facilities

Newfoundland Squid Fishery and Management

141

for both short-term and long-term storage are essential
because spoilage occurs rapidly if the squid are not handled
properly (Learson and Ampola 1977, Botta et al. 1979).
Futher expansion of processing has several advantages in
that processed products may be better able to compete
with innovative products in foreign markets. Marketing
such products may be facilitated further because they are
not restricted by Japanese import quotas. However, mar-
keting such products is complicated by the fact that Japan
presently prefers to purchase unprocessed squid to support
its extensive processing industry. Education in quality
requirements has already been initiated. In 1978 and 1979,
Japanese technicians were present in Canadian plants to
supervise production.

Jigging of squid will probably be encouraged in the
future because squid caught in that manner are in better
physical condition than trawl-caught squid. Presently, the

best quality squid probably come from the Newfoundland
inshore fishery because those squid are caught by jigging
and landed within hours of capture. Also the offshore
jigging of squid will probably be encouraged for reasons of
quality. That method is commonly used in the Japanese
domestic fishery, resulting in as much as 90% of their total
catch of Todarodes pacificus in some years (Rathjen 1973).
In Japan, jigged squid are sometimes sold at a higher price
than trawl-caught squid (Court 1980).

ACKNOWLEDGMENTS

The assistance of J. Drew, H. Mullett, and G. King in
preparing the diagrams is appreciated. Thanks also to
C. Whelan, Economics and Intelligence Branch, Depart-
ment of Fisheries and Oceans, who reviewed the manuscript
and provided helpful comments.

references cited

Ampola, V. G. 1974. Squid-its potential and status as a U.S. food
resource. Mar. Fish. Rev. 36(12):28-32.

Beck, P. C, E. G. Dawe & J. Drew. 1980. Breakdown of 1979 squid
catches in Subarea 3 and Division 4R. with length and sex com-
positions from offshore and Newfoundland inshore commercial
samples. NAFO SCR Doc. 80/11/34, Ser. No. N065. 15 pp.

Botta, J. R., A. P. Downey, J. T. Lauder & P. B. Noonan. 1979.
Preservation of raw, whole, short-finned squid (Illex illecebrosus)
during the period from catching to processing: Skin color of raw
squid and sensory quality of the subsequently cooked squid.
Can. Fish. Mar. Serv. Tech. Rep. 855. 21 pp.

Collins, P. W. & G. P. Ennis. 1978. Breakdown of inshore Newfound-
land squid catches, 1975-77 with length and sex composition
from commercial samples. ICNAF Res. Doc. 78/II/6, Ser. No.
5158. 13 pp.

Court, W. G. 1980. Japan's squid fishing industry. Mar. Fish. Rev.
42(7-8):l-9.

Dawe, E. G. & P. C. Beck. 1980. Assessment of the short-finned
squid (Illex illecebrosus) in Subarea 3 for 1979. NAFO SCR Doc.
80/11/35, Ser. No. N066. 13 pp.

& H. J. Drew. 1981. Distribution and biological charac-
teristics of young short-finned squid (Illex illecebrosus) in the
northwest Atlantic, February 20-March 11, 1981. NAFO SCR
Doc. 81/VI/23, Ser. No. N302. 20 pp.

Durward, R. D„ E. Vessey & R. K. O'Dor. 1980. Reproduction in
the squid, Illex illecebrosus: First observations in captivity and
implications for the life cycle. ICNAF Sel. Pap. 6:7-14.

Ennis, G. P. 1978. A review of the fishery for squid and the general
biological characteristics of the species Illex illecebrosus in the
Newfoundland area. Pages 5.1—5.8 in N. Balch, T. Amaratunga
and R. K. O'Dor (eds.). Proceedings of the Workshop on the
Squid Illex illecebrosus and a Bibliography of the Genus Illex.
Dalhousie University. Halifax, Nova Scotia, May 1978. Can.
Fish. Mar. Serv. Tech. Rep. 833.

Fedulov, P. P. & Yu. M. Froerman. 1980. Effect of abiotic factors
on distribution of young shortfin squids, Illex illecebrosus
(LeSueur, 1821). NAFO SCR Doc. 80/VI/98, Ser. No. N153.
22 pp.

Hodder, V. M. 1964. The Newfoundland squid fishery. Can. Dep.
Fish. TradeNews 17(1):16-18.

Hurley, G. V. 1980a. Recent developments in the squid, Illex
illecebrosus. fishery of Newfoundland, Canada. Mar. Fish. Rev.

42(7-8): 15-22.

. 1981b. An examination of criteria for the short-term fore-

casting of inshore abundance of squid (Illex illecebrosus) at
Newfoundland. NAFO SCR Doc. 80/II/5, Ser. No. N031. 18 pp.

& P. Beck. 1979a. The observation of growth rings in

statoliths from the ommastrephid squid, Illex illecebrosus. Bull.
Am.Malacol. Union. Inc. 1979:23-29.

1979b. Assessment of the short-finned squid (Illex

illecebrosus) in ICNAF Subarea 3 for 1978. ICNAF Res. Doc.
79/11/25, Ser. No. 5351. 19 pp.

& J. Drew. 1979. Breakdown of squid catches in ICNAF

Subarea 3, 1978, with length and sex composition from offshore

and Newfoundland inshore samples. ICNAF Res. Doc. 79/11/27,

Ser. No. 5353. 13 pp.
ICNAF [International Commission for the Northwest Atlantic

Fisheries). 1978. Report of Standing Committee on Research

and Statistics (STACRES). Special meeting on squid, February

191&. ICNAF Redbook 1978:21-33.
. 1979. Report of Standing Committee on Research and

Statistics (STACRES). Special meeting on capeline and squid,

February 1919. ICNAF Redbook 1979:27-46.
Kato, S. 1970. Catching squid by the ton- with pumps. Nat. Fisher-
man 51:14-B-19-B.
Learson, R. J. & V. G. Ampola. 1977. Care and maintenance of

squid quality. Mar. Fish. Rev. 39(7): 15- 16.
Mercer, M. C. 1970. Cephalopod resources and fisheries in the

Northwest Atlantic. Am. Malacol. Union Inc. Annu. Rep.

1970:30-33.
. 1973a. Nominal catch of squid in Canadian Atlantic

waters (Subareas 2-4) 1920 to 1968. ICNAF Res. Doc. 73/73,

Ser. No. 3025. 10 pp.
. 1973b. Distribution and biological characteristics of the

ommastrephid squid Illex illecebrosus (LeSueur) on the Grand
Bank. St. Pierre Bank and Nova Scotian Shelf (Subareas 3 and 4)
as determined by otter-trawl surveys 1970 to 1972. ICNAF
Res. Doc. 73/79, Ser. No. 3031. 11 pp.

. 1973c. Sexual maturity and sex ratios on the ommastre-
phid squid, Illex illecebrosus (LeSueur). at Newfoundland
(Subarea 3). ICNAF Res. Doc. 73/71, Ser. No. 3023. 14 pp.

. 1975. Size distributions of the migrant ommastrephid

squid, Illex illecebrosus (LeSueur) in Newfoundland inshore
waters. ICNAF Res. Doc. 75/27, Ser. No. 3482. 13 pp.

142

DAWF

& G. Paulmier. 1974. Distribution and biological character-
istics of the short-finned squid (Illex illecebrosus) on the conti-
nental shelf of Subareas 3 and 4 in May-June, 1973. ICNAF
Res. Doc. 74/87, Ser. No. 3323. 1 1 pp.

NAFO [Northwest Atlantic Fisheries Organizaion] . 1980. Report of
the Scientific Council. Special meeting, February 1980. NAFO
Scientific Council Report 1979-1980:35-60.

Quigley, J. J. 1964. Mechanized squid jigger. Can. Dep. Fish. Trade
News 17(5):3-5.

Ramalingam, V. 1978. Cuttlefish and squids-Production and
marketing. Indian Seafoods 13(4) & 14(1):8-13.

Rathjen, W. F. 1973. Northwest Atlantic squids. Mar. Fish. Rev.
35(12):20-26.

. 1977. Fisheries development in New England-a perspec-
tive. Mar. Fish. Rev. 39(2): 1-6.

, R. T. Hanlon & R. F. Hixon. 1977. Is there a squid in

your future? Proc. GulfCaribb. Fish. Inst. 29:14-25.

Rathjen, W. I'., R. F. Hixon & R. T. Hanlon. 1979. Squid fishery
resources and development in the northwest Atlantic and Gulf
of Mexico. Proc. GulfCaribb. Fish. Inst. 31:145-157.

Squires, H. J. 1957. Squid, Illex illecebrosus (LeSueur) in the New-
foundland fishing area. J. Fish. Res. Board Can. 14:693-728.

. 1959. Squid inshore in Newfoundland and on the Grand

Bank. 1953-1958. Prog. Rep. Atl. Coast Stn.. Fish. Res. Board
Can. 72:23-26.

Templeman. W. 1966. Squid, Illex Illecebrosus. Pages 122-125 in
Marine Resources of Newfoundland. Fish. Res. Board Can. Bull.
154.

Voss, G. L. 1973. The squid boats are coming. Sea Front 19(4):
194-202.

Journal of Shellfish Research. Vol. 1, No. 2, 143-152, 1981.

THE SHORT-FINNED SQUID (ILLEX ILLECEBROSUS) FISHERY
IN EASTERN CANADA

T. AMARATUNGA

Department of Fisheries and Oceans

Resource Branch. Invertebrates and Marine Plants Division

P.O. Box 550, Halifax, Nova Scotia, Canada B3J 2S7

ABSTRACT The short-finned squid Mex illeeehrosus had traditionally been important to Canada only as a small inshore
fishery in Newfoundland. Fluctuations in inshore landings, common prior to 1975, were probably related to the availability
of squid. Since 1975, the inshore and offshore fisheries have shown tremendous increases in landings.

Historic trends of the fishery are discussed. Recent statistics on the fishery provide information on catch, season, area,
and gear. Offshore statistics prior to 1975 are not complete. Statistics compiled on the international and Canadian offshore
fisheries from the FLASH computer information system has provided a monitor of all activities since 1977.

The historic and present status of the fisheries are presented in relation to the management of the resource.

INTRODUCTION

For many years the short-finned squid Illex illeeehrosus
has been important to Canada only as a small inshore bait
fishery which was concentrated in Newfoundland. In recent
years, however, this species has become commercially
important with the development of international markets.
Since 1975, there has been a dramatic increase in landings
from the inshore fishery in Newfoundland as well as parts
of the Maritimes; a large offshore fishery has also developed
on the Scotian Shelf. Those increases have been related to
increased abundance and increased fishing effort. In this
report, recent international squid catch statistics in eastern
Canada are reviewed, and the historic and present status of
the fisheries are presented in relation to the management of
the resource.

DISTRIBUTION AND FISHERY

Illex illeeehrosus is widely distributed in the northwestern
regions of the Atlantic Ocean. Data compiled from various
sources (Clarke 1966, Roper et al. 1969, Lu 1973, Roper
and Lu 1979) show distribution from Labrador and
Newfoundland to central Florida (Figure 1 ). In a recent
survey, larvae and juveniles of/, illeeehrosus were recorded
in large numbers for the first time in the Scotian Shelf
slope water and Gulf Stream water mix (Amaratunga et al.
1980).

Each year /. illeeehrosus is recruited to the fishery when
a new year-class migrates onto the continental shelf and
inshore areas for the summer and fall. Its distribution in
Nova Scotia (Amaratunga et al. 1978) and Newfoundland
(Squires 1957) waters is usually limited to the warmest
period of the year, from spring (April to May) to late fall
(as late as December). During that period, active fisheries
operate in the Northwest Atlantic Fisheries Organization
Subarea 4 (NAFO SA4) off Nova Scotia and in Subarea 3
(SA3) off Newfoundland (Figure 1 ).

Until the early 1970's, Canadian squid were utilized as
bait for other fisheries. Fishing methods during that time

were mainly limited to inshore jigging operations. Jigging
operations were usually conducted using hand-line jiggers
from small boats. During the early 1970's, Canadian squid
stocks became attractive in the international markets as a
commodity for human consumption. That, in turn, induced
international offshore trawlers to start fishing for squid on
the continental shelves in SA3 and SA4, primarily in SA4.
Offshore trawlers are usually large factory ships fishing
with bottom, off-bottom, or pelagic trawls, as in the fin-
fish fishery. Concurrently, inshore techniques improved
with the use of semi- or totally automated jigger lines.

HISTORIC TRENDS

Nominal catch statistics since 1963 for the entire Illex
illeeehrosus distribution are shown in Table 1 and Figure 2
(from Roberge and Amaratunga 1980). Statistics for SA5-
6 are included to show relative differences from those of
SA2-4. Catches fluctuated in SA2-4 until 1974. Mercer
(1973) reported similar fluctuations in inshore landings
from Nova Scotia between 1920 and 1968. Those fluctua-
tions probably reflect availability of squid, especially in
SA3, and not any change in effort. On the other hand,
relatively large catches in SA4 between 1970 and 1973
probably related to the introduction of offshore trawlers
into the fishery. In SA5-6, a considerable international
offshore squid fishery has been in operation since the late
1960's, accounting for the difference in pattern.

Prior to 1973, the offshore fishery in SA2— 4 was
considered relatively unimportant. Therefore, although
upward trends in landings began in the early 1970's, catch
statistics were incomplete. Often landings alone were
reported with no details on effort and other fisheries
statistics. Also, squid catches were not reported by species
and it is likely that some catches of Loligo pealei were
included in the SA4 statistics (distribution of L. pealei does
not extend into SA3).

After 1973, a concerted effort was made by the Inter-
national Commission for the Northwest Atlantic Fisheries

143

144

AMARATUNGA

85" 80° 75° 70° 65°

Figure 1. Known distribution (shaded area) oUllex Ulecebrosus in the northwest Atlantic region.

SHORT FlNNI I) S(.HTl) I'lSHI RY IN L:\STI RN CANADA

145

0>

o>

IS)
0>

CT>

/

I

A'

\ 1

0>
05

Xi

1
o

1
o

r~

o

1 —

o

o

i

O

o

o

I

o

O)

CO

N

10

in

t

CO

CN

■a
c

S3
c

3
«5

ft.
<

Z

u

<

r-

CO

0)

z

u

5

c

X

u

ft!

Cm

Ul

tr>

(O

JS

o>

U

M

U

3

■a

3

e

CO

e

(0

<

O)

<N

T""

3,

ft.

(0001 X1W) H01V0 1V101

146

AMARATUNGA

TABLE 1.

Nominal catches (metric tons) of Ulex illecebrosus by Subareas,
1963-1979 (from Roberge and Amaratunga 1980).

Subareas

Total

Total
SA5-6

Year

2 3

4

SA2-4

1963

2,199

103

2,222

1.210 1

1964

10,408

369

10,777

193 1

1965

7,831

433

8,264

563 1

1966

5,017

201

5,218

1.562 1

1967

6.907

126

7,033

2,662*

1968

9

47

56

4,948'

1969

21

65

86

2,802*

1970

111

1,274

1,385

2,45 3 '

1971

1,067

7,299

8,906

4,036 2

1972

26

1,842

1,868

14.713 2

1973

2 620

9,255

9,877

15.178 2

1974 31 17

389

437

16.653 2

1975

3,764

13,993

17,757

13,790 2

1976

11,254

30,510

41,764

27,717 2

1977

6 32,748 3

47.199 3

79,953 3

24,792 3

1978

45,472 3

53.118 3

98.590 3

17,695 3

1979

81,820 s

71.279 3

153.099 3

Combined /. illecebrosus and L. pealei, USSR catches included.
Excludes USSR catches which did not report /. illecebrosus and
L. pealei separately.
Preliminary data.

(ICNAF) to obtain complete statistics for individual species
(ICNAF Redbook 1973). Offshore catch statistics were
then obtained at the end of the season from each vessel
operating in the ICNAF area. In 1977, the Foreign Licensing
and Surveillance Hierarchy (FLASH) computer information
system was introduced by Canada to monitor all offshore
fishing activities in SA3 and SA4. As input into the system,
all actively fishing vessels were required to provide informa-
tion weekly on the area fished, catch by species, and effort.
These data were stored in the computer to permit immediate
access to fisheries information. Statistics on the inshore
fishery were obtained from sales slips which contained
information on catch weight, date, areas, and gear used.

The weekly catch for the international offshore fishery
in SA3-4 from 1977 to 1979 is summarized from FLASH
data in Table 2. Because FLASH reports Canadian domestic
catches separately, those are excluded from Table 2. Figure 3
depicts cumulative catch in SA3-4 for 1977, 1978, and
1979. In 1977, with no opening date for the fishery, the
catch began to increase the week of 20 May; fishing was con-
centrated between the weeks of 10 June and 9 September.
In 1978, with an opening date of 15 June, fishing was
concentrated between the week commencing 23 July and
the week of 1 October. The 1979 fishery opened on 1 July
and fishing was concentrated between the week commencing
8 July and 4 November. It must be noted that in all three
years participating countries fished within quota allocations.

In 1978, FLASH reported a total of 29,570 metric
tons (MT) of squid caught offshore by the international

fishing fleet; 2,922.3 MT and 26,647.7 MT were caught in
ICNAF SA3 and SA4, respectively. Sixty-four percent
(SA3) and 95.8% (SA4) of the total squid catch was a result
of directed fishing. Directed and nondirected squid catches
fluctuated throughout the year in SA3 without apparent
pattern. However, in SA4, directed fishing was concentrated
between the weeks of 23 July and 6 August (Figure 4),
while three smaller peak periods occurred in the weeks
commencing 27 August, 17 September, and 29 October.

Effort (reported in days fished) was high during the
months of July and August. Catch rates, however, fluctuated
over the year with highs of 20.32 and 22.68 MT occurring
during the weeks of 30 July and 5 November, respectively.

In 1979, FLASH reported a total catch by the inter-
national fishing fleet of 44,5 10 MT in SA3-4; 2,144.8 and
42,365.2 MT were caught in SA 3 and SA4, respectively.
Ninety-six percent (SA3) and 82% (SA4) of the total squid
catch resulted from directed squid fishing. In SA3, directed
and nondirected squid catches once again fluctuated
throughout the year without apparent pattern, while, in
SA4, fishing was concentrated over a 17-week period from
15 July to 4 November. Intensive directed fishing occurred
between the weeks of 15 July and 2 September (Figure 5).
Effort showed a similar pattern. The highest catch rates
occurred in the months of July and September, 22.44—
23.79 and 20.77-21.85 MT, respectively.

Fish catch statistics are usually reported in units of
weight such as metric tons. In the squid fishery, statistics
given in weight are deceptive because the numbers of squid
landed per-unit-weight change rapidly throughout the
fishing season due to their rapid growth (Amaratunga
1980). This is demonstrated in Table 3 where the 1978
and 1979 international offshore directed catches in SA4
are translated into number of individuals removed. The
number of squid being landed has been a major considera-
tion in the resource management of J. illecebrosus ( Amara-
tunga et al. 1978).

HISTORY OF FISHERY MANAGEMENT

The International Commission of the Northwest Atlantic
Fisheries was instated in 1949 (renamed Northwest Atlantic
Fisheries Organization [NAFO] in 1979), to provide
fisheries management advice to the coastal countries of
the Northwest Atlantic. However, until 1974, the squid
fishery of the ICNAF area was considered to have no com-
mercial importance and, hence, no advice was provided.
The history of subsequent advice provided by ICNAF and
NAFO is summaried below. Because the most important
management regime has been the Total Allowable Catch
(TAC), this is listed separately; other regimes, such as
opening dates for the fishery, are listed under the remarks
column. It should be noted here that the United States
withdrew from ICNAF in 1976, and TAC for SA5 and
SA6 are shown only for those years in which they were
recommended by ICNAF.

SHORT-FINNED SQUID FISHERY IN EASTERN CANADA

147

TABLE 2.

FLASH catch statistics for the international squid ([Ilex illecebrosus) fishery
summarized by week and year for Subareas 3 and 4.

Total Squid Catch (MT)

Total Squid Catch (MT)

Week

Year

Subarea 3

Subarea 4

Subaieas 3 and 4

Week

Year

Subarea 3

Subarea 4

Subareas 3 and 4

1977
1978
1979

255.1
61.0

975.2
666.3

3,234.5

975.2

921.4

3,295.6

1977
1978
1979

557.3
362.3

1.726.3
1,715.7
2,351.1

1,726.3
2,273.0
2,713.4

1977
1978
1979

0.4
368.4
137.5

1.344.3
1,413.3
3.588.6

1,344.7
1,781.7
3,726.1

1977
1978
1979

0.1
255.8
294.8

1,551.3

829.4
2,024.4

1,551.4
1,085.2
2,319.2

1977
1978
1979

128.7
189.3

441.8
1,279.1
2,026.2

441.8
1,407.8
2,215.5

1977
1978
1979

0.2
93.9
67.9

598.4
1,389.2
1,580.0

598.6
1,483.1
1,617.8

1977
1978
1979

0.1

97.0

292.8

854.7
1,249.2

1,434.6

854.8
1,346.2

1.727.4

1977
1978
1979

10.0
121.3

853.9

585.4

1,154.0

853.9

595.4

1.275.1

1977
1978
1979

10.0
1.5

592.9

420.4

1,171.8

592.9

430.4

1.173.3

1977
1978
1979

47.4

71.0

722.2

1,415.5

71.0

769.6

1,415.5

1977
1978
1979

137.3

28.5

967.5

1,190.3

28.5

967.5

1,327.6

1977
1978
1979

—

106.9

778.3

1,074.3

106.9

778.3

1,074.3

1977
1978
1979

85.8
0.02

75.2
388.3
732.6

161.0

388.3
732.6

1977
1978
1979

53.3

164.3

98.0

227.0

164.3

98.0

280.3

1977
1978
1979

—

128.8
8.0

128.8
8.0

1977
1978
1979

13.0

37.7

50.7

1977
1978
1979

6.3

6.3

1977
1978
1979

220.7
2,922.3
2,144.8

40,715.0
26,647.7
42,365.2

40,935.7
29,570.0
44,510.0

16

1977
1978
1979

0.3

17

1977
1978
1979

1.0

18

1977
1978
1979

8.7

19

1977
1978
1979

18.0

7.2

20

1977
1978
1979

10.2

31.3

0.3

21

1977
1978
1979

—

171.8
21.5

4.2

22

1977
1978
1979

19.4
0.4

480.6
19.7

3.5

23

1977
1978
1979

1.0
8.2

955.2
35.1

23.5

24

1977

1978
1979

4.0

2.6

1,706.5
38.9
61.6

25

1977
1978
1979

—

2,295.4

28.5

196.6

26

1977
1978
1979

2.0

215.2

9.8

3,942.9

74.6

393.7

27

1977
1978
1979

23.3

67.9

5.0

3,476.4
201.4
392.5

28

1977
1978
1'979

210.1
14.2

2,828.8

213.6

1,493.4

29

1977
1978
1979

35.0
196.6
108.5

3,849.9

358.8

1.965.7

30

1977
1978
1979

16.4
47.7
98.1

3,753.1
3,286.3
2,926.4

31

1977
1978
1979

21.0

70.9

144.2

3,967.9
6,848.1
4,591.8

32

1977
1978
1979

3.0

136.1

32.8

2,054.2
2,001.1
3,862.8

33

1977
1978
1979

141.6
10.6

1,636.6

971.3

3.244.3

0.3

1.0

8.7

18.0
7.2

10.2

31.3

0.3

171.8

21.5

4.2

500.0

20.1

3.5

956.2

43.3
23.5

1,706.5
42.9
64.2

2,295.4

28.5

196.6

3,944.9
289.8
403.5

3,499.7
269.3
397.5

2,828.8

423.7

1,507.6

3,884.9

555.4

2,074.2

3,769.5
3.334.0
3,024.5

3,988.9
6,919.0
4,736.0

2,057.2
2,137.2
3,895.6

1,636.6
1,112.9

3,254.9

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

Total

148

AMARATUNGA

§ 30

o

X 20'

o

(-
<

<

10.

A 1977
■ 1978
• 1979

* *

10 20 30 10 20 30 10 20 30 10 2(

APRIL

20 3^ if3 2TJ 35 10 2TJ 30 i^ 2% 30 iE 2(5 35 i!) 25 3b
JULY AUGUST SEPTEMBER OCTOBER NOVEMBER DECEMBER

Figure 3. Cumulative catch (MT) of /Ilex in ICNAF Subareas 3 and 4 in 1977, 1978, and 1979 as reported to FLASH.

Short-Finnld squid fishery in Eastern Canada

149

7000 r

6000

Directed
Non ■ directed
Effort

3000

X

u

2000

1000

_

15
MAY

SUBAREA 4

V'x

400

300

o

<

en

200

100

30 15 30 15 30 15 30 15 30 15 30 15

JUNE JULY AUGUST SEPTEMBER OCTOBER NOVEMBER

30

Figure 4. Directed and nondiiected squid catch and effort as reported to FLASH for 1978.

3000

2000

x
u

1000

Directed

■ — — Non- directed
' Effort

n200

o

100

>

15

30

15

30

15

30

15

30

15 30

15

30

15

MAY

JUNE

JULY

AUGUST

SEPTEMBER

OCTOBER

NOVEMBER

Figure 5. Directed and nondirected squid catch and effort as reported to FLASH for 1979.

150

Amaratunga

TABLE 3.

Estimated number of fllex illecebrosus removed by the international-directed squid fishery in Subarea 4, 1978 and 1979.

1978

1979

Directed

Directed

Squid

Estimated

Estimated

Cumulative

Squid

Estimated

Estimated

Cumulative

Catch

Mean Weight

Number

Estimated

Catch

Mean Weight

Number

Estimated

Date

Week

(MT)

(gm)

of Squid

Number

Date

Week

(MT)

(gm)

of Squid

Number

lun

25

26

36.5

Jul

2

27

161.4

137.9

1.17x

10 6

1.17 x 10 6

Jul

1

27

5.0

137.12

3.65 x

10 4

3.65 x 10 4

9

28

164.5

134.8

1.22 x

10 6

2.39x 10 6

8

28

852.6

133.95

6.37 x

10 6

6.41 x 10 6

16

29

357.2

138.4

2.58 x

10 6

4.97 x 10 6

15

29

1,559.8

138.08

1.13 x

10 7

1.77 x 10 7

23

30

3,905.1

189.6

2.06 x

10 7

2.56 x 10 7

22

30

2,354.8

149.90

1.57 x

10 7

3.34 x 10 7

30

31

6,828.8

159.9

4.27 x

10 7

6.83 x 10 7

29

31

3,209.1

159.78

2.01 x

10 7

5.35 x 10 7

Aug

6

32

1,899.5

171.1

1.11 X

10 7

7.94x 10 7

Aug

5

32

2,587.0

169.66

1.52 x

10 7

6.87 x 10 7

13

33

924.3

179.8

5.14 x

10 6

8.45 x 10 7

12

33

2,517.0

179.54

1.40 x

10 7

8.27 x 10 7

20

34

650.9

189.8

3.43 x

10 6

8.80 x 10 7

19

34

2,719.0

189.42

1.44 x

10 7

9.71 x 10 7

27

35

1.572.7

199.3

7.89 x

10 6

9.59 x 10 7

26

35

2,198.1

199.30

1.10 x

10 7

1.08 x 10 8

Sep

3

36

1,413.3

209.4

6.75 x

10 6

1.03 x 10 8

Sep

2

36

3,496.1

209.18

1.67 x

10 7

1.25 x 10 8

10

37

818.1

219.3

3.73 x

10 6

1.06 x 10*

9

37

1,952.5

219.06

8.91 x

10 6

1.34 x 10 8

17

38

1.157.5

229.2

5.05 x

10 6

1.11 x 10 8

16

38

1,965.8

228.94

8.59 x

10 6

1.42.x 10 8

24

39

1,389.2

239.1

5.81 x

10 6

1.17 x 10 8

23
30

39

40

1,555.9
1,329.2

238.83
248.71

6.51 x

5.34 x

10 6

10 6

1.49.x 10 8
1.54 x 10 8

Oct

1

40

1,249.2

248.8

5.02 x

10 6

1.22 x 10 8

Oct

7

41

1,079.2

258.59

4.17 x

10 6

1.58 x 10 8

8

41

582.1

258.7

2.25 x

10 6

1.24 x 10 8

14

42

1,158.1

268.47

4.31 x

10 6

1.63 x 10 8

15

42

378.8

268.7

1.41 x

10 6

1.26 x 10 8

21

43

1,340.6

308.18

4.35 \

10 6

1.67 x 10 8

22

43

716.9

309.0

2.32 x

10 6

1.28 x 10 8

28

44

1,085.4

311.49

3.48 x

10 6

1.70 x 10 8

29

44

955.6

312.3

3.06 x

10 6

1.31 x 10 8

Nov

5

45

748.6

314.5

2.38 x

10 6

1.34 x 10 8

Nov

4

45

1,024.8

313.75

3.27 x

10 6

1.74 x 10 8

12

46

327.4

277.5

1.18 x

10 6

1.35 x 10 8

11

46

671.6

275.54

2.44 x

10 6

1.76 x 10 8

19

47

97.3

292.2

3.33 x

10 6

1.35 x 10 8

18

47

220.1

291.82

7.54 x

10 s

1.77 x 10 8

26

48

8.0

—

—

—

History of Illex illecebrosus Resource Management

Year

Total Allowable Catch

(TAC)

(x 10 3 MT)

Catch
(x 10 3 MT)

Remarks
(Catch x 10 3 MT)

1974

1975

No TAC

No TAC

SA2-4 = 0.4 1973 catch: 9.9 in SA2-4; 15.2 in SA5 and SA6.

SA5 and SA6 = 16.7 Catch constitutes both Illex and Loligo.

Commercial catches incidental and not taken in a directed

fishery.
Pilot whale-consumption study suggests potential catch
could be substantially greater.

SA2— 4 = 17.8 1974 catches considered commercially unimportant.

SA5 and SA6 = 13.8 Catches suggest Illex forms a stock complex from

SA2- 6, with a spring migration northward from
SA5 an