Full text of "Proceedings of the National Shellfisheries Association"

See other formats

PROCEEDINGS

NATIONAL SHELLFISHERIES
ASSOCIATION

OCT 1 7 1978

VOL. 68

PROCEEDINGS

OF THE

NATIONALSHELLFISHERIES ASSOCIATION

OFFICIAL PUBLICATION OF THE NATIONAL

SHELLFISHERIES ASSOCIATION;

AN ANNUAL JOURNAL DEVOTED TO

SHELLFISHERY BIOLOGY

VOLUME 68

Published for the National Shellfisheries Association, Inc. by
The Memorial Press Group, Plyniouth, Massachusetts

JUNE 1978

PROCEEDINGS

OF THE

NATIONAL

SHELLFISHERIES

ASSOCIATION

CONTENTS Volume 68 - June 1978

List of Abstracts by Author of Technical Papers Presented at 1977 NSA
Annual Meeting, Hunt Valley, Maryland, and NSA Coast Section,
Tumwater, Washington v

Gordon Gunter and W. David Burke

Further Notes on How Oysters Land When Planted 1

Frederic Lipschultz and George Krantz

An Analysis of Oyster Hatchery Production of Cultched and Cultchless

Oysters Utilizing Linear Programming Optimation Techniques 5

Herbert Hidu, William G. Valleau and Fletcher P. Veitch

Gregarious Setting in European Oysters - Response to Surface

Chemistry vs. Waterbone Pheromones 11

Richard A. Lutz and Herbert Hidu

Some Observations on the Occurrence of Pearls in the Blue Mussel,

Mytilus edulis L 17

George E. Krantz and John F. Chamberlin

Blue Crab Predation on Cultchless Oyster Spat 38

Jack M. Whetstone and Arnold G. Eversole

Predation on Hard Clams, Mercenaries mercenaries by Mud Crabs,

Panopeus herbstii 42

Paul A. Haefner, Jr.

Seasonal Aspects of the Biology, Distribution and Relative Abundance
of the Deep-Sea Red Crab, Geryon quinquedens Smith, in the Vicinity
of the Norfolk Canyon, Western North Atlantic 49

Hubert J. Squires and G. Riveros

Fishery Biology of Spiny Lobster (Panulirus argus) of the Guajira

Peninsula of Colombia, South America, 1969-1970 63

Abstracts

NSA Annual Meeting

NSA Pacific Coast Section 75

LIST OF ABSTRACTS BY AUTHOR OF TECHNICAL PAPERS

PRESENTED AT THE 1977 NSA ANNUAL MEETING

HUNT VALLEY, MARYLAND

Erik Baqueiro and Craig B. Kensler

Mexican Molluscan Fisheries of the Gulf of Mexico and the

Caribbean: 1970-1975 75

Robert S. Brown

A Disease Survey of New England Soft-Shell Clams, Mya arenaria 75

Robert S. Brown and Carole J. OToole

Histochemical Analyses of Pigment Accumulations in Mercenaries

mercenaria L. and Mya arenaria L 76

H. Arnold Carr

Culture of Hatchery-Spawned Mercenaria mercenaria in Massachusetts 76

Melbourne R. Carriker

Ultrastructural Evidence that Gastropods Swallow Shell Rasped

During Hole Boring 76

Keith Cooper, Sammy Ray and Jerry Neff

The Interaction of Water Soluble Fractions (WSF) of South Louisiana

Crude Oil and Dermocystidium (Labyrinthomyxa) marina at Varying

Temperatures in the American Oyster, Crassostrea virginica Gmelin 77

N. Dean Dey and Ellis T. Bolton

Tetracycline as a Bivalve Shell Marker 77

William J. Eckmayer

Oyster Reef Cultivation for Cultch Material 77

Arnold G. Eversole

Marking Clams with Rubidium 78

RegGillmor

Suspension Culture of European Oysters (Ostrea edulis L.) 78

Reg Gillmor

Growth Responses of European and American Oysters (Ostrea edulis L

and Crassostrea virginica G.) to Intertidal Exposure 79

Harold H. Haskin

The Onshore Surf Clam Resource along the Southern New Jersey Coast 79

Harold H. Haskin and Susan E. Ford

Mortality Patterns and Disease Resistance in Delaware Bay Oysters 80

Dexter S. Haven, William J. Hargis, Jr. and Paul C. Kendall

The Oyster Industry of Virginia 1931 to 1975 80

Mary T. Hickey

Age, Growth, Reproduction and Distribution of the Bay Scallop,

Aequipecten irradians irradians (Lamarck), in Three Embayments

of Eastern Long Island, New York as Related to the Fishery 80

Herbert Hidu, Richard D. Clime and Samuel R. Chapman

Oyster Setting - Evolution of Commercial Hatchery Technique 81

Sewell H. Hopkins

An Oyster Family Tree: Ancestry of Crassostrea virginica 81

Louis Leibovitz

Bateriologic Studies of Long Island Shellfish Hatcheries 81

Louis Leibovitz and John Hamlin Gordon II

Water Quality Studies of Long Island Shellfish Hatcheries 81

Richard A. Lutz

A Comparison of Hinge-Line Morphogenesis in Larval Shells of
Mytilus edulis L. and Modiolus modiolus (L.) 83

K. S.Naidu

Culture of the Sea Scallop, Placopecten magellanicus in Newfoundland 83

Bruce J. Neilson

Engineering Considerations in the Design of Oyster Depuration Plants 84

George S. Noyes, Harold H. Haskin and Cindy Van Dover

Oil and the Oyster in Delaware Bay 84

Linda Plunket

The role of Uronema marinum (Protozoa) in Oyster Hatchery Production 85

Edwin E. Rhodes and Ronald Goldberg

The Use of Pumped Raceway Systems for the Intermediate Grow-Out

of Hatchery Reared Bivalves 85

R. J. Rhodes, M. Wolff and J.L. Music

Status Report on the Commercial Blue Crab Fishery of

the Carolinas and Georgia 85

VII

Scott E.Siddal

The Development of the Hinge Line in Tropical Mussel Larvae

of the Genus Perna .. . . . 86

Robert S. Steneck, Richard A. Lutz and Robert M. Cerrato

Age and Morphometric Variation in Subtidal Populations of Mussels 86

ABSTRACTS OF TECHNICAL PAPERS PRESENTED AT NSA
1977 WEST COAST SECTION MEETING, TUMWATER, WASHINGTON

John H. Beattie, William K. Hershberger, Kenneth K. Chew and Conrad Mahnken

Breeding Disease Resistance into the Pacific Oyster 88

Rick D. Cardwell

Oyster Larvae Mortality in South Puget Sound 88

Darrell Demory

Helicopter Crabbing 89

Richard A. Eissinger

Disease Control in a Molluscan Shellfish Hatchery 89

Jim Glock

Squaxin Island Manila Clam Reseeding Studies 90

William K. Hershberger

Oyster Breeding: Where Can It Go 90

Chris R. Jones

A Comparison of Survival, Growth, and Yield of Pacific Oysters

(Crassostrea gigas) from Different Sources 90

Mark Miller, Kenneth Chew, Charles D. Magoon, Lynn Goodwin and Chris Jones
Preliminary Report on Manila Clam Reseeding Program at Five Puget
Sound Beaches 91

Thomas L. Richards

Seed Oyster Production in the Salton Sea, California 91

M. A. Toner

Preliminary Studies on the Development of a Synthesized Diet for

Juvenile Oysters, Crassostrea gigas 91

VI11

J. R. Vanderhorst and P. Wilkinson

Clam Resource Measurement for Estimation of Pollution Damage 91

Paul Waterstrat

Musseling in on a New Market 91

Anthony Weaver

Pigeon Point Shellfish Hatchery: Past, Present and Future 93

Ronald Thurber Zebal

Vibrio anguillarum and Larval Mortality in a California Coastal

Shellfish Hatchery 93

Cover

Pearls in the blue mussel, Mytilus edulis.

Photo by R. A. Lutz (See page 17).

Proceedings of the National Shellfisheries Association
Volume 68-1978

FURTHER NOTES ON HOW OYSTERS
LAND WHEN PLANTED1

Gordon Gunterand W. David Burke

GULF COAST RESEARCH LABORATORY
OCEAN SPRINGS, MISSISSIPPI 39564

ABSTRACT

Woodward, Huxley and Moebius saw that oysters always set on the left valve. Later
Stafford, Prytherch and Ranson observed cementation by the left prodissoconch (lar-
val shell). However Cunningham and Ortou stated that Ostrea edulis often come to lie
on the right valve. Apparently this is of little consequence on hard bottom, but in mud
the situation is considered to be harmful for reasons summarized by Needier. Gunter
and McGraw found that oysters culled from clumps landed upside down when planted
in water 59% of the time. This is attributed to poor shape of the oysters.

Natural single oysters numbering 1,423, which had been dredged from wild reefs,
were selected or culled to singles and shovelled overboard into fresh water 1.5 to 3
meters deep. Oysters were seen to stabilize in about the first half meter when thrown
into the water and then fall unchanged, upside down or not, to the bottom.

Out of 4,269 shovel-tosses of the 1,423 oysters (3 each) 2,447 (57%) landed on the
left valve and 1,822 (43% ) landed on the right valve. In three replications of the experi-
ment the preponderance of the total sample came to rest normally on the left or lower
valve, and of the total 488 individuals (34%) consistently settled normally whereas on-
ly 108 individuals regularly came to rest on the dextral valve.

INTRODUCTION AND REVIEW

In an attempt to analyze some of the aspects of
oyster culture a little closer, the writers have con-
tinued work on how single oysters land on the
bottom when thrown overboard. This appears to
be a simple and overly pedestrian matter but it has
an interesting history in the literature, with some
examples of how disagreements and misunder-
standings can occur over simple matters.

The early conchologists showed that the oysters
come to rest on the left or convex valve by attach-
ment (Cf. Woodward 1878), and generally lie that
way, contrary to Anomia and Pecten which rest
on the right valve. Nevertheless, Cunningham
(1885) of the Scottish Marine Station disputed this
view and said that most oysters in the Firth of

Presented at 1976 Annual Meeting of the National Shell-
fisheries Association.

Forth rest on the right valve and are heavily fouled
only on the upper (left) valve. This was quickly
disputed by Hunt (1885), who said that all oysters
attach by their convex (left) valves as stated by
Woodward, Jeffrey and Huxley. Moebius (1885)
quickly affirmed that oysters set with the nucleus
of the left valve attached to the substrate. It is now
well known through the observations of Huxley
(1883), Stafford (1910) and Prytherch (1934) that
the larvae always cement the left valve down. The
"nucleus" of Moebius is the left valve of the pro-
dissoconch or late larval shell stage, which Ran-
son, (1960) found attached even in fossil oysters.
Thus, how oysters set and how they come to lie on
the bottom became confused, at least in the minds
of some people.

And so it would appear that the natural position
of oysters was well settled years ago. Even so,
modern workers have caused further discussion

G. GUNTER AND W.D. BURKE

and according to Orton (1937, p. 14), "In life the
flat or right valve usually rests on the sea-bottom
and is often referred to as the lower one." This
caused Galtsoff (1964, p. 16) to say that "Orton's
(1937) statement... is an obvious oversight." But
Galtsoff overlooked Orton's deferred explanation
on p. 27 which says, "When oysters are thrown in
the water they usually settle with the flat valve on
top. In this position the shell is liable to be washed
about by any water-current and eventually to top-
ple over to rest on its flat side." In short Orton ex-
plains the observations of Cunningham (1885)
while verifying the general ideas and observations
of zoologists concerning setting on the left valve.

With regard to the turning over of the European
oyster, Ostrea edulis L., by currents as observed
by Cunningham (1885) and Orton (1937), we call
attention again to the observations of Emery
(1°68) on the same phenomenon regarding empty
pelecypod shells on the continental shelf.

How Oysters Come to Lie When Planted in the
Water

Orton (1^37, p. 27) said merely in passing that
when oysters are thrown into the water they
usually settle with the flat (right) valve on top.

Needier (1938) applied himself to this question
and came to several conclusions, some of which
confirmed our observations independently, be-
cause we never acquired his paper until the last
moment. They may be summarized as follows:
The normal position of an oyster on firm bot-
tom is with the curved (left valve) down. On
soft bottom they sink by the hinge end with
the "lip" up. In upside down oysters the "lip"
grows upward, producing distortion. For the
best shape oysters should lie in the normal
position.
Oysters smother more readily when upside

down.
About 95% of well-shaped oysters landed right
side up in water over three feet deep. The
same percentage righted themselves within a
foot or two when let in the water upside
down.
Crooked oysters more often land upside down.
Loose shells or other oysters caused oysters to
turn over. Water helps in positioning oysters
and it is better to plant with a tide than on
bare ground.

Galtsoff (1964, p. 16) touched upon this ques-
tion with his statement, "In C. virginica the left
valve is almost always thicker and heavier than
the right one. When oysters of this species are
dumped from the deck of a boat and fall through
water they come to rest on their left valves. I
observed this many times while planting either
small oysters not greater than 2 inches in height,
or marketable adults of 5 to 6 inches."

Other authors seem to have used estimates.
Gunter and McGraw (1974) seem to be the only
workers who have presented quantitative data on
this question. They found in Mississippi that wild
reef oysters separated from clusters and culled into
singles landed right side up only 41% of the time.
However, the oysters used in these trials were
essentially misshapen from having been grown
together and lingering doubts over these results
caused us to re-examine the situation. We might
say here briefly and quickly that we have come to
the conclusion that these results are an example of
what Needier was talking about when he said,
"Crooked oysters more often land upside down."

PRESENT WORK AND RESULTS

The writers carried on a further series of simple
experiments using 1,423 oysters of which 937 were
seed oysters under 50 mm in length. These were
collected from natural reefs in Mississippi Sound
by dredge and most of them were selected as
singles, but some were culled. They were shovel-
led overboard into clear fresh water in swimming
pools 1.5 to 3 meters in depth. Observation was
then made by scuba diving and picking up all the
oysters that landed right side up. Then the upside
down oysters were collected and both sets
counted. This whole process was repeated three
times. The results are given in Table 1 .

The departure of these results from a predic-
table norm based on mere chance is given in Table
2. Actually when this is calculated as the prob-
ability function of a binomial distribution, the
chances that the type of distribution shown here
would occur naturally intrinsically in a 50-50
distribution is less than one in a billion. Translated
from statistical terms to the vernacular, this means
that there is practically no chance that these
results are matters of chance.

HOW OYSTERS LAND

TABLE 1. Resti)ig positions of 1423 "planted" oysters during each of three consecutive trials.

▼ = At rest on right valve
A= At rest on left valve

Total Oysters

Run I.

Run. II.

Run III.

1423

108V

16t>A

101T

155A

126Y

488A

125V

154A

39%

61%

39%

61%

20%

80%

44%

56%

TABLE 2. Comparison of calculated and
observed orientation of 1423 "planted" oysters.

Dextral Sinistral

(Chi Right Valve) (On Left Valve)

Calculated Observed Calculated Observed

712 530 712 893

712 553 712 870

712 460 712 963

Run I.
Run II.
Run III.

Totals

2136

1543

2136

2726

DISCUSSION AND CONCLUSIONS
This all means, as several writers have stated
before, that well-shaped natural oysters do have a
very strong tendency to land right side up when
planted single in the water. One might say that
well-shaped oysters are fitted to fall through the
water in a way that is most likely to lead to sur-
vival after the oyster strikes the bottom. We might
wonder what circumstances throughout the ages
would cause a natural oyster to fall through the
water and what would cause these helpless in-
vertebrates to be so attuned to the environment in
this respect. But whatever the situation, they are
obviously among the most successful marine
animals on Earth being present in all continents
except Antartica, at depths from the surface to

two kilometers, and in such abundance that they
leave organic remains such as the Point au Fer
Reef in Atchafalaya Bay in Louisiana which was
30 miles long in its heyday. As relicts of one single
animal these are probably the largest conglomera-
tions on Earth, for the sometimes larger coral reefs
are formed from the remains of many species of
animals and plants.

Observations made by the scuba divers (W. D.
Burke, Ron Lukens and lohn DeMond) showed
that oysters thrown overboard with a shovel
stabilized themselves within two feet and then
continued to fall in the same way to the bottom.
This confirms the previous statement of Needier
who implies that oysters were held in various posi-
tions at the surface and then released. Looked at
another way, our results indicate that well-shaped
oysters have a 36% better chance of survival on
soft mud where they would die less quickly than
misshapen oysters which might fall wrong 59% of
the time as indicated by Gunter and McGraw
(1974).

Examination of Table 1 shows that oysters fall-
ing through the water in the proper stance, so to
speak, have a tendency to do so on repeated trials,
whereas oysters that fall upside down have a
similar tendency to continue to fall upside down

G. GUNTER AND W. D. BURKE

with repeated trials. This is the conclusion we
would expect if the shape of the oysters modifies
its manner of falling through the water.

The matter of how well oysters survive on
various bottoms when they fall upside down or
right side up is another question and although at
first blush it might seem to be simple, easy and
clearcut, it is a bit more complicated than it first
appears. Be that as it may, we hope to treat that
subject in a subsequent study.

ACKNOWLEDGEMENTS

We thank Mr. Ronald Lukens and Mr. John De-
Mond for assisting us with the diving and Mrs. C.
E. Rasor and Mr. Anthony Becker for the use of
their swimming pools.

LITERATURE CITED

Cunningham, T. J. 1885. The resting position of

oysters. Nature, London 32:597.
Galtsoff, P. S. 1964. The American oyster

Crassostrea virginica Gmelin. U. S. Fish Wildl.

Service. Fish. Bull. 64:1-480.
Gunter, G. and K. A. McGraw. 1974. Basic

studies on oyster culture 1. How do single

oysters land on the bottom when planted? Proc.
Nat'l Shellfish. Assoc. 64:122-123.

Hunt, A. R. 1885. The resting position of oysters.
Nature, London 33:8.

Huxley, T. H. 1883. Oysters and oyster question.
Eng. Illustrated Mag. London 1:47-55, 112-121.

Moebius, Karl. 1885. The resting position of
oysters. Nature, London 33:52.

Needier, A. W. H. 1938. How do oysters land on
the bottom under water? Fish. Res. Bd. Can.,
Oyster Farming Circ. No. 1.

Orton, 1. H. 1937. Oyster biology and oyster-
culture being the Buckland Lectures for 1935.
211 pp., 57 fig. Edward Arnold and Co. Lon-
don.

Prytherch, H. F. 1934. The role of copper in the
setting, metamorphosis and distribution of the
American oyster, Ostrca virginica. Ecological
Monographs 4(1): 47-107.

Ranson, G. 1960. Les prodissoconques (coquilles
larvaires) des Ostreides vivants. Bull. Inst.
Oceanogr. 1(183):1-41.

Stafford, J. 1910. The larva and spat of the Cana-
dian oyster. II. The spat. Amer. Nat.
44:343-366.

Woodward, S. P. 1878. Manual of Mollusca. 3rd
ed. London.

Proceedings of the National Shellfisheries Association
Volume 68-1978

AN ANALYSIS OF OYSTER HATCHERY PRODUCTION

OF CULTCHED AND CULTCHLESS OYSTERS

UTILIZING LINEAR PROGRAMMING TECHNIQUES

Fredric Lipschnltz * and George Krantz

UNIVERSITY OF MARYLAND

CENTER FOR ESTUARINE AND ENVIRONMENTAL STUDIES

CAMBRIDGE, MARYLAND 21613

ABSTRACT

Manpower and operational requirements for cultched and cultchless oyster pro-
duction schedules in a large-scale hatchery were compared using a system of linear
equations and a computer optimization program. The matrix of equations defined
the operational sequence within the oyster hatchery, the resource requirements, and
restrictions, if any. The optimization program minimized a cost objective function
within the constraints defined by the system matrix.

Data for the calculations of the matrix coefficients were taken from records of the
University of Maryland small-scale hatchery and from Dupuy (1973). The hatchery
data provided estimates of manpower requirements for each activity, oyster mor-
tality rates, and equipment costs. Dupuy's paper provided space and density re-
quirements. The temporal sequence of oyster development stages was based on well-
documented literature and observations at the model hatchery.

Results show that labor was the major cost component in all types of hatchery
schedules. The optimal solution involved purchase of large amounts of equipment
which remained idle most of the year, being fully utilized in two pulses during the
year. Constant maximal use of equipment required less equipment but more labor
and therefore increased production costs. Use of the cultched mode of hatchery
operation as opposed to the cultchless resulted in approximately 45% savings in pro-
duction costs.

This study represents the first phase of a long- term project to optimize production
scale oyster hatchery operations. Several problem areas indicated by this model will
be investigated and changes incoporated into a revised formulation.

INTRODUCTION cultched spat to cultchless spat; and (3) test the
This paper describes a mathematical model of design of a production scale oyster hatchery just
the operation of a commercial oyster hatchery. completed at the UMCEES Horn Point En-
Through linear programming (LP) techniques the vironmental Laboratories Cambridge, Maryland,
model has been used to: (1) determine an optimal The goal of this paper is to demonstrate the utility
production schedule and equipment mix for oyster of LP as a tool for economic analyses in produc-
hatcheries, (2) compare hatchery production of tion aquaculture.

•Present Address: Ecosystems Center. Marine Biological LineaI" Programming is a mathematical tech-

Laboratory. Woods Hole, Mass. 02543. nique which determines optimal levels of activity

F. LIPSCHULTZ AND G. KRANTZ

within given resource restrictions, using well-
documented theory (Gass, 1969) and readily
available computer programs. As an analytical
tool, linear programming has been used in a varie-
ty of biological applications (Arroyo, 1965;
Davis, 1967; Swartzman, 1973.) The model form
is a matrix of linear equations describing the pro-
duction or use of restricted resources. The use of
linear equations assumes all functions modelled to
be linear, thereby precluding economies of scale
and exponential cost curves. Since matrices of this
form generally have a large number of possible
solutions, an additional equation, the objective
function, can be defined which is maximized
within the given set of possible solutions to the
matrix. For example, an objective function could
be a series of terms relating the profit in all of the
activity levels, thereby determining the most pro-
fitable solution consistent with the imposed con-
straints.

METHODOLOGY
The temporal sequence used in the model con-
sisted of a 360-day year divided into a 300-day
production period, a 30-day maintenance period,
and 30 days of vacation. The oyster life-cycle was
divided into 15-day periods to consolidate the
model activity into units closely approximating
life stages of oysters in the hatchery culture pro-
cedure. The life-cycle activities and their durations
(Table 1) for cultchless hatchery operation are
based on observations at the University of
Maryland Horn Point hatchery. Each of the life-
cycle activities could be initiated in any of 20

TABLE 1. Definitions and Durations of Life-cycle
Activities Available for Initiation during the Pro-
duction Year.

Duration

No. Activity (Periods)

Grow 1 carboy of algae

Condition 1 oyster

Fill 1 Larval Cone

(600,000 larvae/cone)

Set and harden 1 Mylar sheet

of oysters

Fill 1 trough with oysters for

final hardening

Heat water to condition
oyster for 1 period

periods, although the developmental biology in
the oyster life-cycle obviously precluded certain
choices such as initiating spat set prior to the con-
ditioning and larval stages.

Listed in Table 2 is a set of activities through
which the model could purchase resources, such as
labor and equipment, necessary to conduct the
hatchery operations. Initiation of these activities
(i.e. purchasing of resources) took place prior to
the production year and permitted use of the pur-
chased items throughout the year. This restriction
precluded purchase of additional equipment or
temporary labor during the production year.
Labor to install purchased items is included in the
cost.

TABLE 2. Purchasing Activities and Associated
Costs Initiated Prior to the Production Year.

Cost U.S.
Activity Dollars

Hire labor to work 8 hrs/day

for 15 days

10,000

Buy 1 carboy

Buy 1 Larval cone

250

Buy 1 spat tank and set of

associated Mylar trays

1,180

Buy 1 sq. ft. of hardening trough

Buy 1 conditioning tank

(9 sq.ft.)

100

The resource equations for a period in mid-year
are shown in Table 3. The matrix coefficients are
the levels of the resource (manpower, equipment
or energy) required per unit of hatchery activity.
For example, growing a carboy of algae (activity
1) would require 1 carboy, 30 hours of labor and
produce 55.8 liters of algae with a mean cell con-
centration of 107 cells/ml. The negative sign in-
dicates production as is illustrated in the following
equation:

-55.8X! +84X2 +240X3 + 75X4 < 0

Addition of 55.8 to both sides produces an
equation which limits utilization of algal food to
less than or equal to the algal production. Produc-
tion in successive periods is linked by use of this
convention. Thus, larvae initiated in period 5 and
grown for 15 days would add to the supply of spat
for use in the period 6 activity of hardening the
spat on Mylar sheets.

ANALYSIS OF HATCHERY PRODUCTION

TABLE 3. Matrix Coefficients for Cultchless Hatchery Production Activity Initiated During a Mid-Year
Period.

Resource

No. of carboys

Sq. ft. conditioning space

No. of larval cones

No. of spat tanks

Sq. ft. of trough

Labor (hours)

Liters of food supply (Algal)

Larval supply (Individuals)

1st hardening spat supply

(Individuals)
Final hardening spat supply

(Individuals)
Hot water (gpm)
Oysters (Individuals)

Activity
X, X.

.25

.004

65.25

.625

•55.8

84
—60,000

240
600,000

—240,000

120,000
—60,000

-30

— 1

X, = Grow 1 carboy of algae
X2 = Condition 1 oyster
X3 = Grow larvae

X4 = 1st hardening
X5 = Final hardening
X6 = Heat water

The coefficients in Table 3 were calculated from
the records of a small scale oyster hatchery that
was operated for one year at Horn Point En-
vironmental Laboratories. Labor coefficients were
developed on the assumptions of U.S. union labor
(i.e. 40 hr work week and 30 day annual leave).
The design of a cultchless hatchery and its re-
quisite space, oyster density requirements, and
flow rates for water were taken from Dupuy
(1973). The costs for purchase of equipment sup-
plies and expendible materials are actual figures
for (1976) construction of a pilot production hat-
chery currently in operation at Horn Point.

A cost objective function was chosen for this
model utilizing the costs for purchasing the
resources listed in Table 2. The life-cycle activities
also had associated costs, though they were small
compared to the costs of materials, labor, and
energy.

RESULTS

The initial computer run of the model was made
to optimize the production schedule and minimize
the amount of labor, space, and equipment re-
quired to produce 50 million oysters in the 10-
month cultchless production period. The resource

requirements and production schedule to meet this
constraint are shown in Figure 1. Since the initial
high level of conditioning activity (labelled A),
propagates through subsequent life stages, fully
utilizing the purchased resources, new condition-
ing activity (labelled B,C,D) during the first 10
periods is either low or non-existent. After the
pulse of activity passes out of the system, (e.g.
oyster spat are planted on natural bottom), a new
high level of activity (labelled E) is initiated.

A typical pattern of equipment utilization
shows an initial maximal use followed by several
periods where the equipment is largely idle. This
seemingly non-optimal solution on closer ex-
amination was found to be soundly based. Since
labor to use the equipment was by far the greatest
cost element in the objective function, the model
utilized a mobile labor force shifting from equip-
ment types as it followed the oyster life-cycle.

It is possible within the LP framework to restrict
the level of an activity within a given range,
thereby obtaining a solution in which the hatchery
equipment was more fully utilized in all periods.
The oyster conditioning was therefore constrained
to a level of activity currently used in the HPEL
pilot production hatchery. This restriction limited

F. LIPSCHULTZ AND G. KRANTZ

1 —

2 ....

3 --
4

NUMBER OF CONDITIONED OYSTERS
NUMBER OF LARVAL CONES
NUMBER OF SPAT TANKS
SQUARE FEET OF TROUGH

4 3 2 1

2 5,000 |
20pOO

500
400

250 •
200;

1 5,00 0

300

150 :

10,0 00

200

ioo :

5,000

100

so :

1000

500

2 I-
-+ I

H I-

0 2 4 6 8 10 11 14

FIFTEEN DAY PERIODS

FIGURE 1. Time sequence and activity levels for 50 million oysters/year.

1500

V X X

1/1

§ 1200

CC
<

1/1
a:

LU
CD

900

600

300o

UNCONST RA I NED
CONSTRAINED

15 16

3 5 7 9 11 13

FIFTEEN DAY PERIODS
FIGURE 2. Carboy utilization for algal culture.

all subsequent life stages and activities. Figure 2 ed is less for the constrained mode and the number

compares the time sequence of a particular of periods in full use is longer than the un-

resource for the constrained and unconstrained constrained mode. Table 4 lists all of the equip-

modes of operation. The number of carboys utiliz- ment and labor needs for these two possible hat-

ANALYSIS OF HATCHERY PRODUCTION

TABLE 4. Resource Requirements for Constrained
and Unconstrained Brood Stock in a Theoretical
Hatchery Design to Produce 50 Million Oysters
Per Year by the Cultchless Hatchery Process.

Resource

Not Constrained

Constrained Brood Stock

Cost

($1000)
Carboys

(#)
Condition

(sq.ft.)
Cones

(#)

Spat Tanks

(#)
Troughs

(#)
Manpower

2,688

1,469

195

407

1,017
291

2,968

1,531

191

995
376

chery production schedules. The constrained solu-
tion costs more because of the increased labor
costs associated with conducting several opera-
tions simultaneously as opposed to shifting the
labor force from activity to activity as the produc-
tion pulse passes through the system.

The cultched mode of hatchery operation was
modeled by removing the first hardening activity
(X4) and putting all newly set spat directly into the
hardening troughs. The number of periods re-
quired for maturation was increased to 90 days (6
periods). Table 5 compares the results of this run
with the requirements for production of 50 million
oysters by the cultchless production method. The
total cost for production of spat on cultch was
44% less than by the cultchless method partially
because of space economies and greater survival
after setting, but mostly as a result of the lower
labor requirements.

Finally, the cultched and cultchless modes were
compared using the actual equipment and space
available for the operation of a full scale produc-
tion hatchery at Horn Point. An unrealistic
assumption allowed the hatchery program to hire
unlimited labor, though the cost of the labor to
conduct the various specific procedures remained
constant. An oyster selling activity ($100/1000
oysters) (10c each) was added to replace the pro-

duction quota as a motivating force for the model.
The results in Table 6 indicate a non-optimal pur-
chase of equipment when the hatchery was de-
signed. The non-starred equipment remained idle,
limited by the starred resource. The model output
permits calculation of the percent of idle equip-

TABLE 5. Resource Requirements for Comparison
of Cultchless and Cultched Hatchery Procedures.
Production of 50 Million Oysters Per Year.

Resource

Cultchless

Cultched

Cost

($1000)
Carboys

(#)

Condition
(sq. ft.)
Cones

(#)

Spat Tanks

(#)
Troughs

(#)
Manpower

2,688

1,469

195

407

1,017
291

1,503

753

100

1,042
195

TABLE 6. Comparison of Resources in HPEL
Hatchery Under Cultched and Cultchless Opera-
tion Using a Profit Objective Function.

HPEL Hatchery Design
Resource Cultchless Cultched

Profit

($1000)

175.4

366.9

Carboys

(#)

103

101

Condition

(sq.ft.)

Cones

(#)

Spat Tanks

(#)

12*

Troughs

(#)

140*

Manpower

Oysters

(X1000)

4,320

6,720

"Limiting Constraints

F. LIPSCHULTZ AND G. KRANTZ

ment thereby providing guidance for the optimal
hatchery design. Within the given resource restric-
tions the cultched mode again was more efficient
than the clutchless mode producing more oysters
(48%) than the cultchless mode.

CRITIQUE OF THE MODEL

This model represents the first phase of a long
term project to determine the economic and
biological feasibility of using hatchery-raised
oysters to sustain public and private oyster
fisheries. The modeling effort, in conjunction with
existing conventional biological research pro-
grams, has demonstrated some uses as a tool in
determining the future of aquaculture in the
Maryland portion of Chesapeake Bay. These uses
include satisfying the initial objectives of optimiz-
ing a production schedule and equipment mix for
oyster hatchery production, pointing out con-
trasts between cultched and cultchless hatchery
operation and identifying potential production
bottlenecks due to design errors. Beyond these im-
portant products, modeling efforts can benefit
research by clearly and formally organizing data
on hatchery operation, and indicating where
carefully planned new research or technical im-
provements could be of greatest benefit.

Analysis of the output from this initial modeling
effort suggests several areas which need more
refined equations and/or more data from the ac-
tual operation of a production scale shellfish
hatchery which produces both cultched and
cultchless oyster spat. Operational manpower and
production calculations were based on figures
from a laboratory scale hatchery which set only 10
million spat in 1976. A great economy of scale
which the linear program framework cannot
model, is expected in the operation of a larger
facility in 1977 which should produce 100 million
spat during its first year of operation. Therefore,

during 1977, the HPEL facility is being devoted to
collection of the types of data necessary for the
reformulation of the model. The reformulated
model in addition to performing tasks illustrated
in this report can then be used as a predictive tool,
allowing production modifications to be tested
without disrupting hatchery operation.

ACKNOWLEDGEMENTS

This project was jointly supported by the Uni-
versity of Maryland and by the Fisheries Admini-
stration of the Maryland Department of Natural
Resources.

Current studies at HPEL are also being support-
ed by the NOAA Office of Sea Grant.

Computer time and facilities were provided by
the University of Maryland Computer Service
Center.

We wish to thank Dr. Filmore Bender, Depart-
ment of Agricultural and Resource Economics for
his constructive advice, technical assistance, and
review of the manuscript.

BIBLIOGRAPHY

Arroyo, G.J. 1962. Fish Pond Development Plan-
ning with the help of Linear Programming. FAO
Fisheries Technical Paper 21p.

Davis, L.S. 1967. Dynamic Programming for Deer
Management Planning. J. Wildlife Mgmt.
31(4):667-679.

Dupuy, J.L. 1973. Translation of mariculture
research into a commercial oyster seed hatch-
ery. Proc. World Mariculture Soc. p677-685.

Gass, S.I. 1969. Linear Programming Methods
and Applications. 3rd ed. McGraw-Hill Book
Co.

Swartzman, G.L. 1973. Dynamic Programming
Approach to Optimal Grazing Strategies using a
succession Model for a Tropical Grassland.
Appl. Ecol. ll(2):537-548.

Proceedings of the National Shellfisheries Association
Volume 68-1978

GREGARIOUS SETTING IN EUROPEAN AND

AMERICAN OYSTERS — RESPONSE TO

SURFACE CHEMISTRY vs. WATERBORNE PHEROMONES1

Herbert Hidu, William G. Valleau, and Fletcher P. Veitcli

HERBERT HIDU
DEPARTMENT OF OCEANOGRAPHY

IRA C. DARLING CENTER

UNIVERSITY OF MAINE AT ORONO

WALPOLE, MAINE 04573

WILLIAM G. VALLEAU

DEPARTMENT OF ZOOLOGY

UNIVERSITY OF MAINE AT ORONO

ORONO, MAINE 04473

FLETCHER P. VEITCH

DEPARTMENT OF CHEMISTRY

UNIVERSITY OF MARYLAND

COLLEGE PARK, MARYLAND 20742

ABSTRACT
Action of a waterborne pheromone in gregarious setting was demonstrated by ex-
posing European oyster larvae to extrapallial fluid (EPF) prior to and during exposure
to cultch shell. Both treatments resulted in significant increase in larval setting over
controls, indicating that the setting response can be released without contact with a
treated cultch surface. Cross reactivity of EPF between American and European oysters
was also indicated. Additional experiments should investigate the role of the
pheromone in planktonic movements of larvae.

INTRODUCTION 1965, 1974; Bayne, 1969). Various test materials,
In 1949, Cole and Knight-Jones discovered Le" fractionated oyster tissue extracts and ex-
"gregarious setting" in the European oyster trapalhal fluid (oyster shell liquor), they state,
Ostrea edulis L. larvae. The presence of were effective only when applied to surfaces,
postmetamorphic oysters stimulated, in some When test chemicals were administered in suspen-
manner, the setting of larvae near the site The s.on or solution there was no observable modifica-
authors surmised that a waterborne material tion of the behavior of the larvae and a change in
released by the juveniles stimulated the mature Settmg rateS dld not result- They sPeculate that it
larvae to set. Since that time British workers have WOuld be imProbable that a larva could respond
held the strong opinion that gregarious setting is t0 a waterborne material because of very low con-
mediated by the direct contact of larvae with com- centratloris or the material in all but the immediate
pounds adhered to the setting surface (Crisp, SOurce area (boundry laVer theory). Further, they

hypothesize that a small animal, such as an oyster

1 IraC. Darling Center Contribution No. 119 larva, could not sense a concentration gradient

H. HIDU, W.G. VALLEAU AND F.P. VEITCH

and that their swimming speeds are so low that
they could not effectively approach the source
(Crisp, 1965).

Our developing information with the American
oyster (Crassostrea virginica), however, indicates
the action of a waterborne pheromone (Hidu,
1969; Keck et al., 1970; Veitch and Hidu, 1971).
Spat enclosed in bags of plankton mesh too small
for passage of larvae stimulated setting on cultch
outside the bags. Addition of extrapallial fluid
(EPF) or seawater which had contained adult
oysters significantly increased setting rates within
one to two hours. Of course, there is the possibili-
ty that the administered materials became adhered
to the cultch surfaces and the larvae responded to
surface contact after all, as suggested by Crisp
(1974).

To really understand and manipulate recruit-
ment in oysters it is important that we determine
the mechanisms of action in gregarious setting,
i.e., response to surface attached molecules
and/or response to waterborne materials. A set-
ting response released only after surface contact
would mean that mature larvae are benthic and
undergo extensive random "searching" of the bot-
tom until the "proper" substrate is encountered.
With the relatively low current velocities just at
the bottom and feeble swimming speeds of larvae,
it is difficult to conceive how a surface contact
response alone could be of significant benefit in in-
creasing the efficiency of setting of larvae. Rather,
the response would be highly adaptive if pelagic
mature larvae could sense the presence of a large
adult population and then become benthic and set
in the immediate area. Indeed Welch (1930) and
Crisp (1965) suggested such a mechanism; the
response to a dissolved chemical being coupled to
a second sense, i.e., a light response. Photoposi-
tive larvae would turn photonegative, thus caus-
ing the larvae to reach a desirable setting area.
This behavior, possibly coupled with the response
to specific surface chemistry, would be more ad-
vantageous to the setting larvae. Thorson (1964)
suggested that oyster larvae were photopositive
throughout their larval life, but then turned
photonegative and set in response to environmen-
tal stimuli such as increased temperatures en-
countered in the intertidal zone. The sudden ap-
pearance of the larval eyespot just prior to setting

is highly suggestive that this receptor is functional
in setting in some manner.

In the present experiments, European oyster lar-
vae were exposed to extrapallial fluid applied in
suspension prior to and during exposure to cultch
shells in order to demonstrate the release of a set-
ting response through the waterborne action of the
setting pheromone. Further, the cross reactivity of
EPF of American and European oysters has been
determined for these species.

This study was supported in part by National
Science Foundation Grant No. GA-28741 and by
NOAA, Office of Sea Grant, Project No.
NG-40-72.

MATERIALS AND METHODS

All tests determining effects of EPF on setting
were conducted in a similar manner. European
and American oyster larvae were first reared by
methods described by Walne (1966) and Loosanoff
and Davis (1963).

Trials were run with eyed larvae which had in-
itiated setting in large 400-liter culture vessels.
Larvae were concentrated from the larger vessels
and then aliquoted into a series of 1-liter beackers
which each contained five bay scallop, Ae-
quipecten irradians, shells as cultch. Each beaker
contained approximately 5000 larvae with five to
ten replicates per treatment. Twenty-five mis of
EPF was added to 1-liter of larval suspension in
the appropriate series. The experiment was then
held for one to two hours to allow significant
numbers of larvae to attach to the shell cultch. All
vessels were then emptied at the same time and the
cultch shells were gently dipped in clear seawater
to remove larvae from the shells that had not set.
This process, no doubt, removed some newly set
larvae; however, all repetitions were carried out in
a uniform fashion to permit a valid measurement
of the effect of the treatment on setting. Cultch
shells were dried and the total number of larvae
that set were counted under a binocular micro-
scope. The results were analyzed by calculating
the 95% confidence limits of the mean, ±2 SE„,,
or by subjecting results to a single classification
ANOVA where appropriate (Steel and Torrie,
1960).

Extrapallial fluid, intra-and interspecies trials. The
effects on setting of EPF administered in suspen-

GREGARIOUS SETTING OF OYSTERS

sion, was determined first at the intraspecies level
and then at the interspecies level. With American
oysters, an initial series of 12 experiments tested
the effects of American oyster EPF by comparing
setting rates with untreated controls. Later, a
single experiment determined the effects of Euro-
pean oyster EPF on American oyster setting by
comparing its performance with American oyster
EPF and untreated controls. Similarly, with Euro-
pean oysters, 7 experiments were performed to
determine the effects of intraspecies EPF and two
with interspecies EPF. Significant differences in
oyster set between control and EPF treated
cultures within each experiment were determined
by a "t" test (Steel and Torrie, 1960).

American oyster EPF was procurred by first
holding in-season scrubbed oysters out of water
for two to three hours. The shells were then gently
pried open with an oyster knife and the EPF
removed. This procedure generally produced
several mis. of a rather viscous yellow fluid with a
protein concentration of 90 to 100 ug/ml. This
procedure was not possible with European oysters
because this species retains less EPF and prying of
the fragile shells resulted in damage to our
valuable brood stock animals. An alternate
method was devised, that of allowing 36 air-dried
oysters to pump in a single 3-liter volume of sea
water for two hours. Oysters readily transferred
EPF to this medium; however, the protein concen-
trations were much lower, approximating 20
ug/ml.

Extrapallial fluid — action of waterborne vs. at-
tached chemicals.

We felt that waterborne action could be further
demonstrated if prior exposure of oyster larvae to
EPF in suspension resulted in increased setting
rates after transfer to experimental cultures con-
taining only seawater and cultch, but no EPF. A
series of four experiments was thus set up to deter-
mine setting rates for European oyster larvae
which were pretreated in two ways (Figure 4). The
first group was held in a 60-liter vessel with the ad-
dition of 6 liters of EPF from European oysters
(procurred as above). Larvae were stirred to pre-
vent prolonged contact with container surfaces.
After 10 minutes, larvae were decanted onto a
sieve, thoroughly washed with filtered seawater
and placed in a second 60-liter vessel made up to

the same volume with EPF-free seawater. A se-
cond 60-liter vessel with larvae served as a con-
trol. Concentrations of larvae in the vessels ap-
proximated 5000 per liter.

Three experimental treatments were initiated,
i.e.,

a. Control larvae with no EPF (10 reps)

b. Control larvae with 25 mis EPF added to
experimental cultures

c. Experimental larvae pretreated with EPF but
with no addition of EPF to experimental
cultures. (EPF released).

Results from each of the four repetitive ex-
periments were analyzed with a single classifica-
tion ANOVA. Significant differences among
treatments were determined with an lsd test (Steel
and Torrie, 1960).

RESULTS

Intraspecies response to EPF. Extensive trials with
American and European oysters indicate that
there is a very rapid response to EPF administered
in suspension (Figure 1). One to two hours of ex-
European oyster larvae

H r-

©O© ©

European oyster ex <r opolhal fluid

0 30 60 90 120 150

Total Set per Experiment
American oyster larvae

H h

©@® @© © © I

American Oy

r a pa 1 1 ia • i u - J

■12 ' i ' I

-no odd.t m

40 60 80 100

Total Set per Experiment

FIGURE 1. Setting of European and American
oyster larvae in response to intraspecies extrapal-

H. HIDU, W.G. VALLEAU AND F.P. VEITCH

Hal fluid administered in suspension. Seven ex-
periments were run with European oyster larvae
and 12 with American oysters, with ten replicate
cultures in each experiment. "T" tests revealed
significant differences in all experiments at least
at the 95% level.

posure resulted in over twice the setting in ex-
perimental cultures. Gross examination revealed
that setting behavior is activated within 10
minutes of application of EPF. Shells extracted
from experimental cultures at this time had greater
numbers of larvae loosely attached in a swim-
crawl phase preparatory to setting.

Additional trials with both species indicated a
possible interspecific response, although the
results were variable for unknown reasons. With

European oyster larvae Expt.

1 1

Cor

trol -

ropol

trapol
ioi f I

■ al f

Uld

American oysler ei
no additive

0 I 2 1

5 6 7 8 9 10 i

Set per Culture

European oyster larvae Expt. 2

1
1 *

, 1 _,
1

Europeon oyster extrapal

Amencon oyster ex trapaiiiai fluid
I - no additive

ial

luid

■:.

6 10 12 14 16 16 20 22 24

Set per Culture

FIGURE 2. Setting of European oyster larvae in
response to extrapallial fluid of American and
European oysters. Points indicate replicate cul-
tures within each experiment. Mean values of rep-
licates and 95% confidence limits (±2 SEm) are
indicated.

European oyster larvae, for example, a first trial
with American oyster EPF (Figure 2) resulted in a
very significant increase in setting rates. A second
trial, however, resulted in a very little increase
over untreated controls. A preliminary trial with
American oyster larvae indicated increased setting
in response to European oyster EPF (Figure 3) .

American oyster larvae

1 ,

ial r

Uld

4).

Cont

Europeon oyster enlropol

American oytler eitrapoliial tluid
no additive

0 2

B 10 12 14 16 IB 20 22 24

Set per Culture

FIGURE 3. Setting of American oyster larvae in
response to extrapallial fluid of American and
European oysters. Points indicate replicate cul-
tures with mean value and 95% confidence limits
indicated.

Exposure of European oyster larvae to EPF prior
to exposure to cultch shells resulted in significant
increases in setting, demonstrating a waterborne
action of the pheromone (Figure 4). Two of four
repetitions of the experiment resulted in significant
differences between treatments, with controls be-
ing significantly lower than the groups exposed to
EPF and rinsed, which were in turn lower than the
groups exposed to EPF during the exposure to
cultch shell. Two other experiments, although
they showed similar numerical trends showed no
overall significant differences as revealed by the
ANOVA.

Thus, oysters of both species are immediately
stimulated to set in response to EPF administered
in suspension. The response appears to be in-
terspecific. The action of a waterborne material is
indicated with European oysters because the larval
setting response was released by exposure to
suspended EPF prior to exposure to cultch shells.

GREGARIOUS SETTING OF OYSTERS

EUROPEAN

OYSTER SET

Expt.

Control

EPF

Released

EPF

121 **

(Total of 10 cultural

100

)

141

130 NS

124 NS

114

**
414

Total

218

437

789

OtSTER EXTRA PA LLIAL FLUID

HOLD LARVAE
10 MIN

CONTROL WATER
WITH TREATED LARV*

E XTRAPAL LI A L
FLUID

,,.0 b",ebb LJ»"> Q»'o

^ ' COUNT SET

FOUR EXPTS

FIGURE 4. Setting of European oyster larvae in
response to intraspecies extrapalhal fluid adminis-
tered prior to and during exposure to cultch shells.
An appropriate ANOVA analyzed significance of
differences in each of four experiments.

DISCUSSION

These experiments add evidence that oyster set-
ting is initiated through action of waterborne
chemicals. Thus there appears to be an additional
component to the gregarious setting response not
generally recognized by the British workers.
However, the mechanism of action of waterborne
materials is obscure, again by reasons stated
previously. The attractive option is that water-
borne pheromones present in the vicinity of very
large concentrations of oysters act to draw larvae
from the plankton by modifying their photo- or
geotaxis. American oyster populations, in the
American mid-Atlantic region at least, in their un-
disturbed state are, or were, concentrated on huge
bars of many acres surrounded by vast expanses

of mud bottom. It would be quite expedient for
larvae to "recognize" these areas, drop from the
plankton, and begin exploring the bottom, with
then at least some chance of encountering a
favorable attachment surface.

We have tried to measure change in larval geo-
and phototaxis by administering EPF under condi-
tions of light and dark in small-scale water col-
umns. Results were interesting but inconclusive
because of inadequate experimental apparatus.
Needless to say, it would be very instructive to
demonstrate positive geotaxis or negative
phototaxis which is released by the presence of
waterborne chemicals from oysters. Realistic-sized
experimental water columns with precise control
of environmental factors would be a necessity.

These experiments indicated considerable cross
reactivity of EPF between Crassostrea and Ostrea,
and this suggests that chemicals emitted from
oyster populations may modify recruitment rates
in other species; that is, act as kairomones as
described by Kittredge et al (1974). It is not hard
to imagine the adaptive value of such evolution;
predators may locate prey (Welch, 1930; Crisp,
1965); larvae of epifaunal species may detect a
substrate favorable for epifauna; finally the most
intriguing possibility, interspecies setting re-
sponses may be the biological basis for the
establishment of many marine benthic com-
munities. The British (Meadows and Campbell,
1972) appear to have considerable evidence for in-
terspecies response for many groups but tend to
dismiss its importance in favor of the dominant in-
traspecies response. Much remains to be ac-
complished in determining the ecological
significance of the chemical senses in marine
meroplankton, but their potential diversity of
form and function cannot be disputed at this
point.

LITERATURE CITED

Bayne, B. L. 1969. The gregarious behavior of the
larvae of Ostrea edulis L. at settlement. J. Mar.
Biol. Assoc. U.K. 49:327-356.

Cole, H. A. and E. W. Knight-Jones. 1949. The
setting behavior of larvae of the European
oyster, Ostrea edulis L., and its influence on
methods of cultivation and spat collection. Fish.
Invest., Lond. Ser. II 17(3):39 pp.

H. HIDU, W.G. VALLEAU AND F.P. VEITCH

Crisp, D. J. 1965. Surface chemistry, a factor in
the settlement of marine invertebrate larvae.
Botanica Gothoburgensia III, Proc. of the Fifth
Marine Biological Symposium, Goteburg, 1965,
pp. 51-65.

Crisp, D.J. 1974. Factors influencing the settle-
ment of marine invertebrate larvae. In: P. T.
Grant and A. M. Mackie (eds.), Chemorecep-
tion in Marine Organisms, Academic Press,
London, pp. 177-265.

Hidu, H. 1969. Gregarious setting in the American
oyster, Crassostrea virginica Gmelin. Chesa-
peake Sci. 10(2):85-92.

Keck, R., D. Maurer, C. Kauer, and W.A. Shep-
pard. 1970. Chemical stimulants affecting larval
settlement in the American oyster. Proc. Nat.
Shellfish. Assoc. 61:24-28

Kittredge, J.S., F.T. Takahashi, J. Lindsey and R.
Lasker. 1974. Chemical signals in the sea:
marine allelochemics and evolution. Fishery
Bull. 72(1):1-11.

Loosanoff, V. L. and H. C. Davis. 1963. Rearing
of bivalve mollusks. In: F. S. Russell (ed.), Ad-

vances in Marine Biology, Academic Press,
London, 1:1-136.

Meadows, P.S. and J. I. Campbell. 1972. Habitat
selection by aquatic invertebrates. In: F.S.
Russel (ed.), Advances in Marine Biology,
Academic Press, London, 10:271-382.

Steel, R. G. D. and J. H. Torrie. 1960. Principles
and Procedures of Statistics. McGraw-Hill
Book Co., Inc. New York. 481 pp.

Thorson, G. 1964. Light as an ecological factor in
the dispersal and settlement of larvae of marine
bottom invertebrates. Ophelia 1:167-208.

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

Walne, P. R. 1966. Experiments in the large scale
culture of the larvae of Ostrea edulis L. Fish. In-
vest. Lond., Ser. II 25(4):l-53.

Welch, J. H. 1930. Reversal of phototropism in a
parasitic water mite. Biol. Bull. Woods Hole
59:165-169.

Proceedings of the National Shellfisheries Association
Volume 68-1978

SOME OBSERVATIONS ON THE OCCURRENCE OF
PEARLS IN THE BLUE MUSSEL,

MYTILUS EDULIS L.'

Richard A. Lutz2 and Herbert Hidu

DEPARTMENT OF OCEANOGRAPHY
UNIVERSITY OF MAINE
WALPOLE, MAINE 04573

ABSTRACT

Pearl incidence in raft and shore populations of mussels (Mytilus edulis L.) of
similar lengths was quantitatively compared in four separate experiments in the
Damariscotta River and Boothbay Harbor, Maine. Highly significant differences be-
tween the two population types were found in each of the experiments, with fewer and
smaller pearls occurring in raft-based individuals. A positive correlation was observed
between the number of pearls in mussels of similar lengths sampled from each of the
rafted populations and the amount of time the rafted substrate had been in the water.
The relationship between number of pearls per mussel and age was qua)itified for one
rafted and one shore population of mussels in South Bristol, Maine. No significant age-
independent differences were found between the two populations with regard to the
quantity of pearls present. Quantification of differences in pearl incidence between
geographically isolated Mytilus edulis populations should facilitate correlation of the
presence and quantity of pearls with the presence and abundance of the definitive
and/or intermediate host(s) of the digenetic trematode parasite reputedly responsible
for the initiation of pearl formation.

INTRODUCTION isolated pearls from specimens of M. edulis

According to Giard (1907), the first documented sampled from certain areas along the Gaspe' coast

account of the presence of pearls in mussels of Canada. More recently, Scattergood and

(Mytilus edulis L.) was given by Olaus Worm in Taylor (1949) have reported pearls in various

1655 upon examination of mussels taken near mussel populations along the northeast coast of

Copenhagen. Since that time, various workers the United States from Eastport, Maine, to Cape

have commented on the presence of pearls in Cod, Massachusetts. In all of the studies above,

isolated M. edulis populations. European in- considerable variation in both number and size of

vestigators have reported pearl-infested mussels in pearls with geographical location has been

a number of localities along the coasts of Den- reported. Such variable incidence has resulted in

mark, France, and England (Garner, 1857; d'Ham- the designation of distinct pearl-producing areas

onville, 1894; Dubois, 1901, 1909; Jameson, 1902; and is of considerable biological interest. Factors

Herdman, 1904; Giard, 1907). Stafford (1912) responsible for the observed differences have been

the research subject of several workers (Garner,

' Contribution number 110 of the Ira C. Darling Center. 1872; Dubois 1901, 1909; Jameson, 1902; Scat-

Umversity ot Maine at Orono, Walpole, Maine 04573. , , .

■ Present address: Department of Geology and Geophysics, Yale tergood and 1 aylor, 1949).

University, New Haven, Connecticut 06520 The independent studies of Garner (1872) and

R.A. LUTZANDH.HIDU

Dubois (1901) showed pearl incidence in M. ednlis
to result from infection by a parasitic trematode.
Jameson (1902) described the organism which, ac-
cording to Odhner (1905), is probably Gytn-
nophallus bursicola. Since Jameson's description,
considerable work has been done to ascertain the
life cycle of the distome parasite (Odhner, 1905:
Nicoll, 1906; Giard, 1907; Dubois, 1907a, b,
1909). Thus far, the suggested life cycle involves
either the common eider duck, Somateria
mollissima, and/or the black scoter, Oidemia
nigra, as the definitive host(s) and the blue mussel,
M. edulis, as the intermediate host (Dubois,
1907b; Jameson and Nicoll, 1913; Stunkard and
Uzmann, 1958). Whether a second intermediate
host is required remains uncertain (Nicoll, 1906;
Dubois, 1909; Stunkard and Uzmann, 1958). In
general, therefore, the life cycle of the trematode is
not well established and attempts at further
unravelling the cycle have been frustrated largely
because of taxonomic chaos. This is emphasized
by the statement of Stunkard and Uzmann (1958,
p. 298), "specific identification (of gymnophallids)
is so uncertain that we prefer to list the worms by
host and location rather than propose names that
might further confuse the taxonomic situation.''

During the past century, various workers have
speculated on factors responsible for the presence
or absence of pearls in various populations of
mussels (and, hence, factors controlling the
distribution patterns of the trematode initiating
pearl formation). Of these, salinity has been allud-
ed to by two workers. Jameson (1902, p. 143)
stated that the "most favorable places (for pearl
formation) seem to be estuaries or landlocked
channels", while Dubois (1909) observed that
pearl-bearing populations were frequently located
at the mouths of rivers. d'Hamonville (1894), stu-
dying a bed of "rnoulieres perlieres" in Billiers (a
borough in Brittany, France near the mouth of the
Vilaine), could detect no differences between
various environmental parameters (sediment, cur-
rent velocity, seaweed distribution, and plankton)
of the pearl-infested area and those of an adjacent
area harboring "rnoulieres sans perles". Lack of
contact of the mussel with the sediment has been
suggested as contributing to reduced pearl in-
cidence by both Jameson (1902) and Nicoll (1906)
based on studies of the creeping motion of the sup-

posed cercaria of the gymnophallid responsible for
initiation of pearl formation. Furthermore,
Jameson (1902) observed reduced pearl incidence
in mussels taken from stakes or floating objects,
although Dubois (1909) found pearls within
Mytilus galloprovincialis on ropes in the ex-
perimental culture operations at the University of
Lyon. A final factor, and one which has received
only limited attention, is that of age. d'Hamon-
ville (1894) commented that pearls were only
found in the largest and less regularly formed
mussels {"celles qui sont le mains regulierement
formees") at Billiers, while Jameson (1902) ob-
served that pearls were seldom found in mussels
less than 40 mm in length. These stunted and
larger individuals may well have been the older
members of the population. Jameson (1902) at-
tributed the relatively small size of pearls in the
Billiers population to the active mussel fishery in
the area which prevented individual mussels from
reaching "a great age". The effect of age is sum-
marized by Jameson's (1902, p. 162) statement
that the "general experience of everybody ac-
quainted with pearl-fisheries is that the largest
pearls were found in the oldest and thickest shells,
which proves how intimately the growth of pearl
and shell are associated." Despite this realization,
no workers have attempted to quantify the rela-
tionship between the presence of pearls and age.
Furthermore, it has never been demonstrated that
age-independent differences exist between various
populations with regard to the size and quantities
of pearls present. The lack of such quantitative
data in these studies renders conclusions concern-
ing factors responsible for the presence or absence
of pearls highly speculative. It is the purpose of
this study to compare quantitatively the size and
number of pearls in rafted and shore-based M.
edulis populations and to establish if age-
independent differences actually exist between
these two population types.

MATERIALS AND METHODS

Preliminary Studies

1. Pearl Removal and Sorting

Throughout the following studies, pearls were
removed from individual mussels using the
following modification of the potassium hydrox-
ide technique employed by Scattergood and

PEARLS IN BLUE MUSSEL

Taylor (1949). The soft tissues of each mussel were
carefully removed from the shell and placed in a
5% solution of boiling KOH for a period of 10
min. This resulted in complete maceration of the
tissues. The solution was diluted with water and
carefully decanted, leaving the pearl-containing
residue at the bottom. The residue was then
poured through a specially constructed set of
sieves which was rotated and gently shaken under
running water for a period of 3 min. This resulted
in the separation of pearls into one of the follow-
ing six size categories (in microns):

(A) > 1050 (D) 308-471

(B) 602-1050 (E) 153-308

(C) 471-602 (F) 102-153
The total number of pearls per size category was
determined by examination of individual sieves
under a dissecting scope. The selection of the
smallest mesh (102 ^m) was based on two con-
siderations. First, the smallest diameter recorded
for 486 pearls from 10 mussels was 120 pm.
Secondly, no pearls were found on a 50 ^m screen
attached to the bottom of the sieve set during
analyses of 165 mussels which contained a total of
1574 pearls.

2. Homogeneity of Shore Population
A preliminary study was undertaken in Clark
Cove on the Damariscotta River in Lincoln Coun-
ty, Maine, to determine the variability in the
number of pearls per mussel and to test the
homogeneity of a shore population with regard to
pearl incidence. Five stations with dimensions of 1
m2 were established at the mean low water level
(MLW) over a distance of 100 m, with 25 m be-
tween stations. Eleven mussels were gathered from
each station, sampling only those with lengths be-
tween 63.5 and 76.2 mm (2V2 -3"). These were
considered representative of the size mussels nor-
mally gathered commercially. Numbers of pearls
were determined for individual mussels and the
results subjected to a one-way classification
ANOVA.

Shore vs Raft

Pearl incidence in raft and shore populations of
mussels of similar lengths was quantitatively com-
pared in four experiments in the Damariscotta
River and Boothbay Harbor, Maine. Shell lengths
of specimens sampled from the two population
types in Experiments #1 - #3 were restricted to the

size range 63.5 - 76.2 mm. Lack of a sufficient
quantity of rafted mussels with lengths greater
than 63.5 mm in Experiment #4 necessitated the
use of a smaller size range (50.1 - 63.5 mm) for
adequate comparison of the two populations.
1. Experiment #1: Clark Cove Raft (31 2 years)

Specimens of M. edulis obtained from a raft left
in the water approximately 31 -2 years (June, 1968 -
December 17, 1971) were quantitatively compared
with shore specimens of similar lengths with
regard to the size and number of pearls present in
the soft tissues. The raft, which was located in the
Darmariscotta River (Clark Cove), is depicted in
Figure 1. A site with dimensions corresponding to
those of the raft was chosen on the shore at MLW
within 50 m of the raft. The shore site and the
underside of the raft were divided into five sta-
tions (Figure 1). The vertical distance between the
intertidal and subtidal shore stations was less than
0.2 m. On December 7, 1971, 11 mussels were
gathered from each station. The total number of
pearls in each size category was determined for in-
dividual mussels and these numbers combined to
arrive at station and location (shore and raft)
totals. Prior to statistical analysis, a logarithmic
transformation [log (x + 1)] (Steele and Torrie,
1960) was applied to all data since the variance
was found to be approximately proportional to
the square of the mean. Nested analyses of
variance (mussels within stations, within loca-
tions) were run on the transformed values.
2. Experiment #2: Boothbay Harbor Raft (5 years)

Pearl incidence in mussels obtained from a raft
left in the water for approximately 5 years was
quantitatively compared with that in mussels of
similar lengths sampled from an adjacent shore
population. As in Experiment #1, a one-way
hierarchial classification (mussels within stations,
within locations) served as the experimental
design for the following study. The raft, which
had been in the water of Boothbay Harbor since
July, 1967, consisted of a floating wooden bumper
approximately 13 m in length. Five stations with
dimensions of 1 x 0.75 m were selected on the
underside of the raft. Each station was separated
from the adjacent one by approximately 2 m and
numbered consecutively R4A - R4E. The depth of
water under the raft at mean low water varied
from approximately 1 m at the inshore station

R.A. LUTZANDH.HIDU

3 m

EXPERIMENTAL RAFT

MLW

INTERTIDAL

SHORE SAMPLE PLOT

FIGURE 1. Raft and shore stations (Clark Cove, Damariscotta River, Maine) for Experiment §1. MLW
mean low water level.

(R4E) to 7 m at the offshore station (R4A).
Similarly, five stations with dimensions of 1 x 0.75
were located on a mussel bed at MLW on the adja-
cent shore. Again, the stations were spaced at in-
tervals of approximately 2 m. On August 4, 1972,
11 mussels were gathered from each of the 10 sta-
tions. The total number of pearls in each size
category was determined for individual mussels
and the numbers combined to arrive at station and
location (shore and raft) totals. The data were
transformed [log (x + 1)] and the two populations
compared using nested analyses of variance.
3. Experiment #3: Manila Rope (21 months)

A 5/8" diameter Manila rope (2 m in length)
was hung from a floating dock in Clark Cove in
May, 1971. On January 4, 1973, a 0.5 m section of
the rope, suspended 1 m beneath the dock, was

stripped of all attached mussels. Of these, 55
specimens, varying in length from 63.5 - 76.2 mm,
were sampled and subjected to the potassium
hydroxide treatment. The total number of pearls
in each size category was determined for the in-
dividual mussels. Through calculation of Stu-
dent's t values, the transformed [log (x + 1)] data
were compared with the transformed values for
the 55 mussels from the adjacent shore population
described in Experiment #1.
4. Experiment #4: Asbestos Panel (7 months)

An asbestos panel measuring approximately 0.3
m: was placed at a depth of 1 m beneath a floating
dock on the Damariscotta River (Wentworth
Point) in May, 1972. On December 2, 1972, 55
mussels (from natural larval settlement) were
removed from the panel and an additional 55

PEARLS IN BLUE MUSSEL

specimens sampled from an adjacent shore
population at MLW. The total number of pearls in
each size category was determined for each
specimen and the transformed (log (x+1)] values
for both populations compared through calcula-
tion of Student's t values.
Comparison of Rafted Environments

Transformed [log (x+1)] pearl counts from
mussels sampled from each of the rafted en-
vironments assessed in the preceding four ex-
periments were quantitatively compared. Seven
separate analyses of variance were run comparing
totals per mussel and totals for each of the six size
categories. For analyses indicating a difference
among a set of population means, Tukey's w-
procedure was used to judge the significance of
differences between the individual population
means within the set. This test is more conser-
vative than Duncan's multiple range test as the en-
tire experiment is the unit used in stating the
number of errors of the type where an observed
difference is falsely declared to be significant. The
test criterion is

w =q.05(p.n2)(sr)
where q.os is a tabulated value (Steele and Torrie,
1960, p. 445) for p treatments and n2 degrees of
freedom and sr is estimated from the error mean
square, w is used to judge the significance at the
0.05 level of each of the observed differences (Steel
and Torrie, 1960).

Shore vs Raft (Age-Independent Studies)
1. Transplantation

Pearl incidence in mussels left in a rafted en-
vironment for 14 months was quantitatively com-
pared with that in mussels left on an adjacent
shore for the same period of time. On October 19,
1972, 250 mussels with lengths varying from 13.0 -
17.0 mm were gathered from the underside of the

1 Engle and Loosanoff (1944) found the season of setting of
mussels in Milford, Connecticut, to be of comparatively short
duration, extending from the early part or middle of June to the
middle or end of August. Plankton samples of McAlice et al.
(unpublished data) suggest that the vast majority of M. edulis
larvae within the Damariscotta River are present between the
months of May and September. It follows that the greatest pro-
portion of larval settlement in this estuary should be restricted
to these warmer months. In light of these considerations, the
majority of mussels from the two sampled populations are ex-
pected to be restricted to summer year classes. Age estimates in
this study are. therefore, generally considered accurate to
within 1 year.

raft described earlier in Experiment #1. These were
individually notched for subsequent identifica-
tion. Twenty-five individuals were placed in each
of the 10 sections (20 cm long) of cylindrical 5 mm
VEXAR plastic netting with a layflat diameter of
10 cm. Five sections were hung from a raft off
Wentworth Point at a depth of 0.5 m below the
surface. The remaining five stations were placed in
contact with sediment at the mean low water level
on the shore within 50 m of the raft. On December
19, 1973, 65 of the original 125 mussels were
recovered from the shore station and all 125
mussels from the raft. The pearls were removed
from 65 of the 125 rafted specimens and all of the
shore mussels. These were separated into size
categories as previously described. Pearl counts
from the two populations were quantitatively
compared.

2. Regression of Pearls on Age

The regression of the number of pearls per
mussel on age for a rafted M. edulis population
was quantitatively compared with a similar
regression for an adjacent shore population. On
July 26, 1973, 85 mussels of 25 - 96 mm length
were sampled from a raft placed in the water at
South Bristol, Maine in June, 1964. Similarly, 102
mussels varying in length from approximately 19-
92 mm were gathered on the same date from an
adjacent shore population. The pearls were
removed as described earlier and the total number
per individual recorded. One shell valve of each
specimen was embedded in epoxy and
longitudinally sectioned along the antero-
posterior axis. The exposed shell surfaces were
polished and etched and acetate peels prepared for
examination with both compound and dissecting
microscopes. Age estimates were based on counts
of annual growth patterns within the inner shell
layer [See Lutz (1976) for a detailed description of
annual growth patterns within the shell of both
shore and raft-based specimens].1 Occasional sub-
jectivity associated with the counting of lines may
somewhat reduce the accuracy of age estimates for
certain specimens. Such subjectivity, however, is
expected to be equal for both populations and
should have little effect on the interpretation of
differences between the two. As the variance of
pearl counts for individual year classes was found
positively correlated with the mean, actual counts

R.A. LUTZANDH.HIDU

were logarithmically transformed [log (x + 1)1
(Steel and Torrie, 1960). A regression of trans-
formed pearl counts on age was run for each
population, using a total of 78 rafted and 82 shore
specimens. Five of the original 85 rafted mussels
and seven of the original 102 shore specimens were
discarded because of poorly preserved peels or
suspected subjectivity associated with the count-
ing of lines. Two 1-year-old rafted and 13 shore
specimens ranging in age from 10 - 16 years were
also excluded because of the lack of corresponding
age classes in the other population. Differences in
slope and elevation between the two regression
lines were assessed using an analysis of covariance
(Steel and Torrie, 1960; Sokal and Rohlf, 1969).

RESULTS

Preliminary Studies

The Clark Cove shore population (at MLW)
was found to be relatively homogeneous with
regard to the quantity of pearls present in the soft
tissues. Table 1 shows the results of the ANOVA,
with the null hypothesis that no difference exists
between station means other than that due to
chance. The null hypothesis was accepted, sug-
gesting that a sampling site at MLW could be
located randomly at any point along the 100 m
stretch with confidence of obtaining a represen-
tative sample of the population.
Shore vs Raft

Highly significant differences in pearl incidence
were found between rafted and shore-based
populations of mussels. In each of the four ex-
periments, rafted individuals contained fewer and
smaller pearls than mussels of similar length ob-
tained at MLW from an adjacent shore popula-
tion.

1. Experiment #1: Clark Cove Raft (31 2 years)

Specimens of M. edulis obtained from the raft
left in the water for approximately 31 2 years con-
tained significantly fewer pearls than specimens of
similar length obtained from an adjacent shore
population (Table 2). The nested ANOVA in-
dicates a highly significant difference (F =188.83)
between the raft population mean (2.2 pearls per
mussel) and that of the adjacent shore population
(14.3 pearls per mussel). The null hypothesis of no
significant difference between stations means was
accepted.

TABLE 1. Total pearl counts and analysis of vari-
ance for mussels sampled from each of five sta-
tions at the mean low water level in Clark Cove,
Damariscotta River, Maine.

Station

Specimen

Total

190

145

169

Mean

17.3

13.2

8.0

6.6

15.4

Source of

Variation

Among stations

948. 9C

) 237.20 0.84 n.s.

Within stations

14957.11

282.06

Total

15906.01

In addition, pearls found in the rafted mussels
were significantly smaller than those obtained
from the examined shore specimens. Results of the
six separate analyses of variance (Table 3) il-
lustrate that the shore population mean number of
pearls in any size category is significantly greater
at the 0.01 level than the mean for the raft popula-
tion in any corresponding size category. Further-
more, no pearl was found in this study with a
diameter greater than 1 mm in any raft-based in-
dividual. No significant differences between sta-
tion means (experimental error) were shown in
any of the size category analyses.
2. Experiment §2: Boothbay Harbor Raft (5 years)

Pearl incidence in mussels obtained from the
raft left in the water for approximately 5 years was
significantly lower than that in specimens of
similar length from the adjacent shore population
(Table 4). The null hypothesis (for the nested
ANOVA) of no significant difference between
locations (shore and raft) was rejected, with the
shore population mean (27.7 pearls per mussel)
considerably greater than the mean of the rafted

PEARLS IN BLUE MUSSEL

TABLE 2. Total pearl counts and analysis of variance for raft and shore mussels in the Damariscotta
River (Clark Cove)."

Raft"

Station

Shorec

Specimen

Total

170

L69

155

122

170

Raft

mean =

2.25

Shore mean =

14.29

Source of Variation

Among stations

11.78

1.31

Locations

11.33

L88.83**

Among stations w

ithin li

jcations

0.45

0.0b

0.38 n.s.

(experimental

error

Among mussels w

thin stations

100

16.33

0.16

(sampling error)

Total

109

28.11

"The results of the analysis of variance are based on transformed [log(x + 1)] pearl counts.
'Rafted specimens were obtained from a raft left in the water approximately 31 2 years (June, 1°68
December 17, 1971).

'Shore specimens were gathered at the mean low water level within 50 m of the raft.
* indicates significance at the 0.01 level.

TABLE 3. Analyses of variance for individual size category pearl counts from raff and shoreb mussels in
the Damariscotta River (Clark Cove).'

Size

Transformed

category

Population

mean

dev.

>1050fjm

Raft"

Shoref

0.66

0.1426

0.2231

4.7375**

602-1050 Mm

Raft

Shore

0.71

0.1765

0.2130

6.1498**

471-602 Mm

Raft

Shore

0.64

0.1560

0.2140

5.3979**

308-471 Mm

Raft

0.02

0.0055

0.0406

Shore

1.38

0.2746

0.2892

6.9000**

153-308 Mm

Raft

0.07

0.0219

0.0789

Shore

3.09

0.3848

0.3648

7.3760**

102-153 Mm

Raft

Shore

1.05

0.1861

0.2818

4.8974**

"Student's t values were calculated using transformed [log(x + 1 )] pearl counts.

"Rafted specimens were obtained from an asbestos panel suspended at a depth of 1 m beneath a float-
ing dock for approximately 7 months (May-December 2, 1972).
cShore specimens were gathered at the mean low water level within 50 m of the raft.
* 'Indicates significance at the 0.01 level.

TABLE 10. Analyses of variance and results of Tukey's w-procedures for total and individual size cate-
gory pearl counts."

Source of Variation

Total Number of Pearls
df

Among Rafts
Within Rafts

Total

3
216

4.7677
22.8338

1.5892
0.1057

219 27.6015

w = q 05(4,216)sr = 3.63(0.0438) = 0.0438

Raft Rl" R2< R3" R4<

Mean

0.0274

0.0770

0.3402

0.3487

15.0353*

Source of variation

Size category >1050 Mm
df

Among Rafts
Within Rafts

3
216

0.0012
0.0890

0.0004
0.0004

.0000 n.s.

Total

219

0.0902

PEARLS IN BLUE MUSSEL

Source of variation

Size category: 602-1050 f^rn

df SS

Among Rafts
Within Rafts

Total

3
216

219

0.1795
2.3123

2.4918

W = q 05(4,216)5* = 3.63(0.0140) = 0.0506

Raft

Mean

R2
0.0109

R4
0.0274

0.0748

0.0598
0.0107

5.5888**

Source of variation

Size category: 471-602 ^m

df SS

Among Rafts
Within Rafts

Total

Source of variation

3
216

219

0.3259
3.4878

3.8137

0.1086
0.0162

w = q 05(4,216)sr + 3.63(0.0172) = 0.0623

Size category: 153-308 /^m

df SS

6.7058'

Raft
Mean

Rl R2 R3

0 0 0.0455

0.0930

Size category: 308-471 /jm

Source of variation

Among Rafts
Within Rafts

3
216

0.7538
9.8919

0.2513
0.0458

5.4869**

Total

219

10.6457

= q 05(4,216)sj = 3.63(0.0289)

= 0.1048

Raft
Mean

Rl R2 R3

0.0055 0.0164 0.1122

R4
0.1400

Among Rafts
Within Rafts

Total

3 1.3038

0.4346

216 14.2086

0.0658

219 15.5124

= q 05(4,216)sF = 3.63(0.0346) = 0.1255

Raft

Rl R2 R3 R4

Mean

0.0219 0.0524 0.1680 0.2064

6.6069*

R.A. LUTZANDH.HIDU

Source of variation

Size category: 102-153 ^m

df SS

Among Rafts

3 0.6160

Within Rafts

216 7.8973

Total

219 8.5133

= q 05(4,216)sr= 3.63(0.0258) = 0.0936

Raft

Rl R2 R3 R4

Mean

0 0.0055 0.0917 0.1212

0.2053
0.0366

5.6093*

"Mussels were sampled from substrates left in the water for varying lengths of time.

"Rl = Asbestos Panel (May, 1972 - December 2, 1972)

•R2 = Clark Cove Rope (May, 1971 - January 4, 1973)

JR3 = Clark Cove Raft (June, 1968 - December 17, 1971)

<R4 = Boothbay Harbor Raft (July, 1967 - August 4, 1972)

"Indicates significance at the 0.01 level.

#4 and the amount of time for which the rafted
substrate had been in the water (Table 10). The
null hypothesis of no significant difference be-
tween pearl counts in mussels from the four rafted
substrates was rejected for six of the seven
analyses of variance (Table 10), the only non-
significant difference occurring for pearls with
diameters greater than 1050 ^m. Although
Tukey's w-procedure failed to show a significant
difference (at the 0.05 level) between each of the
individual population means, examination of the
transformed means for the totals indicates a
general trend for an increasing number of pearls
per mussel with increasing length of submergence
of the substrate from which the specimens were
collected. With the exception of minor discrepan-
cies, this same general trend holds true for the
population means calculated for each individual
size category.

Shore vs Raft (Age-Independent Studies)
1. Transplantation

No significant difference in pearl incidence was
found between mussels left in a rafted environ-
ment for 14 months and specimens left on an adja-
cent shore for the same period of time. The 65 in-
dividuals which had been on the shore contained a
total of two pearls. These were in two individuals
and the two size categories, 102-153 and 309-471
|im. The 65 individuals examined from the raft
population also contained a total of two pearls in
two individuals. These were found in the two size
categories, 154-308 and >1050 ptm. The pearl

found in the latter size category had a diameter of
approximately 1100 ^m. The identical number of
pearls found in each population rendered
statistical analysis of the data superfluous.
2. Regression of Pearls on Age

No significant age-independent difference in the
number of pearls within the soft tissues was found
between rafted mussels in South Bristol and
specimens obtained from the adjacent shore
population. The total numbers of pearls within in-
dividual mussels in each year class are shown in
Tables 11 and 12 for the raft and shore popula-
tion, respectively. The regression lines and 95%
confidence belts for the regression of the
transformed [log (x + 1)] counts on age are
depicted in Figure 2 for each population. The
regression equations for the raft and shore popula-
tions are, respectively,

ind

Y = 0.1540X — 0.3765

Y = 0.1217X — 0.3266,

where Y is the estimated mean of the transformed
[log (x+1)] pearl counts for a mussel of age X (in
years). An estimate (Y) of the mean number of
pearls per mussel of age X is given in the following
formula from Elliot (1971):

Y = antilog[1.15sr + Y] — 1,

where s,. is the standard error of Y for a given
value of X. Following the procedure outlined by

PEARLS IN BLUE MUSSEL

TABLE 11. The total number of pearls within individual mussels in each year class (raft)."

Raft
(Number of pearls per individual)

Specimen

Year Class

3
0

5 6
0 3

7
7

113

1 9

0 1

0
8

Total

23 13

130

Mean

0.3

1.0

2.6 4.3

2.6

43.3

5.0

"Mussels were samples from a

South B

ristol rafted

population.

Sokal and Rohlf (1969), an estimate of s, for the
raft and shore populations are provided by the
equations

s,. = JO. 1521 [0.0128 + (X — 3.9872)- 1

1447

and

s, = /0.0277 [0.0122 + (X — 5.4268)2]

2739
respectively. Once again, X is the age in years of

the specimen. Insertion of these estimates into
Elliot's formula and substitution of the ap-
propriate values of Y for each population provides
an estimate (Y) of the mean number of pearls per
mussel for both the raft and shore population. The
equations are, respectively,

Y = antilog (1.15 s2 + 0.1540X — 0.3765) — 1
and

Y = antilog (1.15 s,2 + 0.1217X — 0.3266) — 1

R.A.LUTZANDH.HIDU

TABLE 12. The total number of pearls within individual mussels in each year class (shore).

Shore
(Number of pearls per individual)

Specimen

Year

Class

0
11

Total

Mean

0.1

0.7

1.0

3.9

5.1

5.9

7.2

"Mussels were sampled from a South Bristol shore

population at the mean

low water

level.

However, in consideration of the relatively small
magnitude of sj, the comparatively wide 95% con-
fidence intervals, and the subjectivity associated
with the counting of the annual lines on acetate
peels, a relatively accurate estimation of Y for
each population is provided by substitution of ap-
propriate values in the equation

Y = antilogY— 1.

For both populations the linear regression on
age was found to remove a highly significant por-
tion of the variation of the transformed pearl
counts (Table 13). The deviations from regression
were not significant. Table 14 shows the results of
the analysis of covariance comparing the two
regression lines. No significant difference between
the slopes of the regression lines nor between the
adjusted transformed means of the two popula-
tions (elevation of lines) was detected in this
study.

Finally, no pearls with diameters greater than 1
mm were found in mussels less than 5 years old.
Two pearls (one from each population) with
diameters greater than 1 mm were found in 5-year-
old specimens.

DISCUSSION

The results of this study suggest that, with
regard to the size and quantity of pearls in the
mantle tissue, no difference exists between raft-
based mussels and those of comparable age ob-
tained from adjacent shore populations. The dif-
ferences found between mussels of similar lengths
obtained from rafts left for varying periods of time
are probably a reflection of age differences be-
tween the individuals sampled. Similarly, the dif-
ferences observed between raft and shore popula-
tions in this study are probably a reflection of a
difference in the age distribution of specimens
from the two environments. Lutz and Porter
(1977) have shown that a 50 mm mussel is ob-

PEARLS IN BLUE MUSSEL

RAFT

Y= I540X - .3765

•3 '

SHORE

Y= 1217 X - 3266

-l 1 1 1 1— rlXH — S

2 345678902

AGE (years)

FIGURE 2. Regressions of logarithmically transformed pearl counts on age for raft and shore based
mussels. Dashed lines represent 95% confidence belts.

tained in at least one Maine environment in a
period of 12 months from settlement using rafting
techniques. Reported estimates of the average
growth rate of mussels (using length measure-
ments) in natural populations (submerged and in-
tertidal - the North Atlantic region) vary from 1.9
- 16.0 mm per year (Mossop, 1922a, b; Field,
1922). Thus, the rafting of mussels may increase
linear growth rate as much as 3-25 fold over that
of natural benthic populations. Therefore,
although the age structure of the two population
types (raft and shore) in most of the experiments
conducted is not known, the average age of the
shore mussels is suspected to be considerably
greater than that of the rafted specimens.

If the rate of pearl formation and pearl growth

remains relatively constant throughout the life of
a mussel, one might expect little or no difference
between old and young individuals with regard to
the number of pearls in the smallest size category.
The results of Experiments #1 - #4 and the com-
parison of rafts left for varying lengths of time in-
dicate that this is generally not the case. The
greater number of small pearls in shore-based in-
dividuals and in mussels sampled from the rafts
left longest in the water suggest that there is a
general increase in the number of pearls being
formed and/or a decrease in the growth rate of
pearls as the individual ages. Both of these are
probably occurring to some extent. As the in-
dividual ages, there is generally an increase in the
surface area of the mantle epithelium. If, as has

R.A. LUTZANDH.HIDU

TABLE 13. Analyses of variance for regressions of transformed pearl counts on age.

Source of variation

Among year classes
Linear regression
Deviations from regression
Within year classes
Total

Raft

5.8213

0.8316

12.3934**

4.9086

32.2722**

0.9127

0.1521

2.2335 n.s

4.7667

0.0681

10.5880

Shore

Source of variation

Among year classes
Linear regression
Deviations from regression
Within year classes
Total

4.9670

0.7096

6.5945**

4.8010

173.3213**

0.1660

0.0277

2.2574 n.s

8.0720

0.1076

13.0590

"An analysis is shown for each of two populations (raft and shore) in South Bristol, Maine.
* 'Indicates significance at the 0.01 level.

TABLE 14. Analysis of covariance comparing the regressions of transformed pearl counts on age."

Analysis of Covariance

Transformed adjusted raft mean = 0.2375
Transformed adjusted shore mean = 0.3338

Within
Raft
Shore

Pooled, W

Between, B

df x: xy y2 b

77 206.9872 31.8750 10.5880 0.1540
81 324.0610 39.4440 13.0390 0.1217

Total
158 531.0482 71.3190 23.6270 0.1343
Difference between slopes
1 82.8518 5.5404 0.3705

613.9000 76.8594 23.9976 0.1252
Between adjusted means

df SS MS F

7b 5.6794 0.0747

80 8.2379 0.1030 1.3788 n.s.

156 13.9173 0.0892

157 14.0490 0.0895

1 0.1317 0.1317 1.4765 n.s.

158 14.3749

1 0.3259 0.3259 3.6413 n.s.

The analysis compares the regression lines for two populations (raft and shore) in South Bristol, Maine.

been suggested by numerous workers (Garner,
1972; Dubois, 1901, 1909; Jameson, 1902;
Jameson and Nicoll, 1913), pearl formation is a
result of trematode infection, this increased sur-
face area may offer a greater number of sites for
penetration by the parasite, and, hence, would
result in an increased number of pearls. As the ma-
jority of pearls in M. edulis are nacreous, the same

processes controlling thickening of the inner shell
layer may control the growth of pearls. This was
recognized by Jameson (1902, p. 161) who stated
in reference to pearls, "their growth is, in fact,
regulated by the causes which control the thicken-
ing of the shell." Examination of the polished shell
sections and corresponding acetate peels presented
by Lutz (1976) reveals that there is a general

PEARLS IN BLUE MUSSEL

decrease in the width of annual increments with
increasing age of the specimen. A similar decrease
in the growth rate of pearls probably occurs.

Jameson (1902) and Nicoll (1906) claim that the
gymnophallid trematode responsible for pearl for-
mation in M. edulis from French and English
waters enters the mussel as a tailless cercaria.
This, in turn, led Jameson (1902, p. 160) to con-
clude that "in order to be abundantly infected,
Mytilus must be on the bottom." Dubois (1909)
disagrees, claiming to have found all larval stages
of the trematode within the mantle of M. edulis. If
pearls in mussels from Maine waters are also a
result of infection by the trematode, Gym-
nophallus, the results of the present study appear
to discredit the claims of Jameson (1902) and
Nicoll (1906). If a larval stage of Gymnophallus
enters M. edulis, it is a stage that is not restricted
to a bottom habitat.

Dubois (1907b) conducted an experiment to test
the effect of increased temperatures on the
metamorphosis of metacercariae larvae of the
gymnophallid trematode responsible for the initia-
tion of pearl formation. Based on the acquisition
of adult characteristics at higher temperatures (35
- 40°C), he concluded that larval metamorphosis
to the adult form must take place in a warm-
blooded animal. Jameson and Nicoll (1913) sug-
gest that the common eider duck, Somateria
mollisima, and/or the black scoter, Oidemia
nigra, serve(s) as the definitive host(s). Stunkard
and Uzmann (1958) fed metacercaria-infected
mussels from Long Island to newly hatched eider
chicks and recovered adult gymnophallids, pro-
bably G, bursicola (Odhner, 1905), from the in-
testines of the chicks. Both Oidemia nigra and
Somateria mollissima are abundant in certain
areas throughout the Gulf of Maine and either one
or both may serve as the adult host(s) for this
trematode. If pearl formation in these waters is a
result of gymnophallid infection, it is reasonable
to expect the presence and quantity of pearls in
mussels to be somewhat correlated with the
presence and abundance of eiders and/or scoters
in the surrounding waters. Before such a correla-
tion can be made, however, age-independent dif-
ferences (if existent) in pearl incidence between
geographically isolated populations of M. edulis
must be quantified. The results of this study sug-

gest a method of obtaining such quantification.

Several workers (Jameson, 1902; Nicoll, 1906;
Lebour, 1906) have suggested that a second in-
termediate host may be required for completion of
the life cycle of the trematode responsible for pearl
formation. Jameson (1902) found sporocysts con-
taining larvae, almost identical with those which
occur in M. edulis, within the mantle margins of
the bivalves, Tapes decussatus and Cardium
edule. Nicoll (1906), in his examination of
numerous specimens of Cardium edule, failed to
find such sporocysts in the mantle margin, but
noted (P. 149) their frequent occurrence in "one
well-defined, somewhat oval-shaped mass
situated in the middle line dorsally just over the
posterior border of the liver." Neither Tapes
decussatus nor Cardium edule are found within
the Gulf of Maine. Thus, if the trematode
(probably Gymnophallus bursicola) responsible
for the initiation of pearl formation in Maine
waters requires a second intermediate host for the
completion of its life cycle, such a host remains to
be found. Furthermore, if this trematode is
responsible for the initiation of pearl formation in
Maine waters and if one and only one additional
intermediate host is required, the presence and
quantity of pearls in mussels should be correlated
with the distribution patterns of this host. Again,
the results of this study suggest a method of quan-
tifying differences (independent of age) between
geographically isolated M. edulis populations
with regard to pearl incidence, facilitating correla-
tion of the presence and quantity of pearls with
the presence and abundance of such a host.

ACKNOWLEDGEMENTS

This work was supported by NOAA Grants
1-36099, NG-40-72, 04-3-158-63, 04-3-158-38,
04-5-158-50, 04-6-158-44056, SGI-77-17, and
04-7-158-44034. We thank Drs. David Dean,
Franklin Roberts, and Michael Mazurkiewicz for
their guidance and critical reviews of initial drafts
of the manuscript; Dr. Bernard J. McAlice and
Mr. William Soule, Jr. for their advice and direc-
tion with the statistical aspects of this work; Mr.
Barnaby Porter for his helpful suggestions and
assistance, particularly in the design and construc-
tion of numerous experimental rafts used

R.A. LUTZANDH. HIDU

throughout this study; Mr. Keith Leeman and Mr.
Kenneth Fossett for assistance in setting up
lapidary equipment; Miss Phyllis Coggins and Mr.
Richard D. Smith for their assistance with graphic
illustrations; Miss Patricia Higgins for typing the
manuscript; and especially Miss Sarah E. Hurlburt
for constantly reminding the senior author that
there are more important things in life than
Mvtilus edulis L.

LITERATURE CITED

d'Hamonville, B. 1894. Les moules perlieres de
Billiers. Bull. Soc. Zool. France 19:140-142.

Dubois, R. 1901. Sur la mecanisme de la forma-
tion des perles fine dans le Mytilus edulis. Com-
pt. Rend. Hebd. Seances Acad. Sci., Paris
133:603-605.

Dubois, R. 1907a. Sur les metamorphoses du
Distome parasite des Mytilus perliers. Compt.
Rend. Seances Soc. Biol. 63:334-336.

Dubois, R. 1907b. Action de la chaleur sur le
distome immature de Cymnophallus margar-
itarum. Compt. Rend. Seances Soc. Biol.,
63:502-504.

Dubois, R. 1909. Contribution a l'etude des perles
fines de la nacre et des animaux que les produi-
sent. Ann. Univ. Lyon n. s., 29:1-126.

Elliot, J. M. 1971. Some methods of the statistical
analysis of samples of benthic invertebrates.
Freshwater Biol. Assoc. Sci. Publ. No. 25, 144

P-
Engle, J. B. and V. L. Loosanoff. 1944. On the

season of attachment of larvae of M. edulis

Linn. Ecology 25:433-440.
Field, I. A. 1922. Biology and economic value of

the sea mussel, Mytilus edulis. Bull. U. S. Bur.

Fish. 38:127-259.
Garner, R. 1857. On the pearls of the Conway

River, North Wales, with some observations on

the natural productions of the neighboring

coast. Brit. Ass. Adv. Sci., Part 2, p. 92-93.
Garner, R. 1872. On the formation of British

pearls and their possible improvement. J. Linn.

Soc. 11:426-428.
Giard, A. 1907. Sur les Tre'matodes margar-

itigenes du Pas-de-Calais (Gymnophallus

somateriae Levinsen et G. bursicola. Odhner).

Compt. Rend. Seances Soc. Biol. 63:416-420.

Herdman, W. A. 1904. Recent investigations on

pearls in shellfish. Proc. Trans. Liverpool Biol.

Soc. 17:88-97.
Jameson, H. L. 1902. On the origin of pearls.

Proc. Zool. Soc, London 1:140-165.
Jameson, H. L. and W. Nicoll. 1913. On some

parasites of the scoter duck (Oedemia nigra)

and their relation to the pearl-inducing

trematode in the edible mussel (Mytilus edulis).

Proc. Zool. Soc, London, p. 56-63.
Lebour, M. V. 1906. Notes on Northumbrian

trematodes. Rep. Scient. Invest. Northumb. Sea

Fish. Comm. 1905, p. 100-105.
Lutz, R. A. 1976. Annual growth patterns in the

inner shell layer of Mytilus edulis L. J. Mar.

Biol. Ass. U. K. 56:723-731.
Lutz, R. A. and B. Porter. 1977. Experimental

culture of blue mussels (Mytilus edulis L.) in

heated effluent waters of a nuclear power plant.

Proceedings of the Eighth Annual Meeting,

World Mariculture Society, January 9-13, San

Jose, Costa Rica, Louisiana State University

Press (in press).
Mossop, B. K. E. 1922a. A study of the sea mussel

Mytilus edulis Linn. Contr. Canad. Biol.

2:17-48.
Mossop, B. K. E. 1922b. The rate of growth of the

sea-mussel (Mytilus edulis L.) at St. Andrews,

N. B., Digby, N. S. and in Hudson Bay. Trans.

Roy. Canad. Inst. 14(3):3-22.
Nicoll, W. 1906. Notes on trematode parasites of

the cockle (Cardium edule)and mussel (Mytilus

edulis). Ann. Mag. Nat. Hist. 17:148-155.
Odhner, T. 1905. Die Trematoden des arktischen

Gebietes. In: Romer u. Schaudinn, Fauna Artica

4(2):291-372.
Scattergood, L.W. and C. C. Taylor. 1949. The

mussel resources of the North Atlantic region.

Part II. Observations on the biology and the

methods of collecting and processing the

mussel. Comm. Fish. Rev. ll(10):ll-23.
Sokal, R. R. and F. J. Rohlf. 1969. Biometry. W.

H. Freeman and Company, San Francisco,

776p.
Stafford, J. 1912. On the fauna of the Atlantic

coast of Canada, third report-Gaspe,

1905-1906. Contrib. Canad. Biol. 1906-1912, p.

45-67.
Steel, R. G. D. and J. H. Torrie. 1960. Principles

PEARLS IN BLUE MUSSEL 37

and procedures of statistics. McGraw-Hill Book on digenetic trematodes of the genera Gym-
Company, Inc. New York, 481p. nophallus and Parvatrema. Biol. Bull.
Stunkard, H. W. and J. R. Uzmann. 1958. Studies 115:276-302.

Proceedings of the National Shellfisheries Association
Volume 68-1978

BLUE CRAB PREDATION ON CULTCHLESS OYSTER SPAT

George E. Krantz and John V. Chamberlin

UNIVERSITY OF MARYLAND

CENTER FOR ENVIRONMENTAL AND ESTUARINE STUDIES

HORN POINT ENVIRONMENTAL LABORATORIES

BOX 775

CAMBRIDGE. MARYLAND 21613

UNIVERSITY OF MARYLAND

DEPARTMENT OF AGRICULTURE ENGINEERING

COLLEGE PARK, MARYLAND

ABSTRACT

Many cultchless oyster spat (Crassostrea virginica) planted experimentally on
natural bottoms in Maryland portions of the Chesapeake Bay in 1975 and 1976 have
been destroyed by blue crabs (Callinectes sapidus). High mortalities (79 to 99%) were
observed within one month after oysters ranging from (3 mm-40 mm) in diameter were
placed directly on natural bottom or in trays without closed tops. Oysters in enclosed
trays at these locations exhibited no unusual mortality. Several patterns of shell
destruction (chipped shell edges, a single puncture over the adductor muscle, broken
area of original spat attachment, and opposing notches on the shell edges) were observ-
ed among the oyster shells collected from the field. The same destruction patterns were
observed when cultchless oyster spat were placed in aquaria containing adult blue
crabs. Cultchless oyster spat which produce high quality half-shell oysters if grown in
protected containers, may be of little value when planted on natural bottom in
Maryland to sustain native oyster stocks, or to obtain an economical return from a
planted private lease.

INTRODUCTION

Crabs of various species are important
predators on oyster spay. Stone crabs (Menippe
mercenaria) are a serious problem in the States
bordering the Gulf of Mexico. So are green crabs
(Carcinus maenas) and mud crabs (Neopanope
texana) in New England states (Galtsoff, 1964).
Mud crabs were incriminated in very high mor-
talities (as high as 50 percent) of Connecticut
oyster spat less than 10 mm long by MacKenzie
(1970). Several authors have also noted that the
blue crab, Callinectes sapidus. can cause high
levels of mortality in natural oyster and clam
populations in the Middle Atlantic and Gulf States
(Lunz, 1947; Menzel & Hopkins, 1955). Menzel &

Hopkins (1955) observed the feeding behavior of
blue crabs in floating cages and found that a single
crab can consume up to 19 oyster spat per day.

Castagna (1970) suggests that predation by blue
crabs is the major constraint in the culture of hard
clams on natural bottoms. Without some form of
protection, clam mortality can approach 100 per-
cent (Menzel et al, 1976; Castagna et al, 1970).

The same constraint — predation by crabs —
has been encountered in our attempts to grow
cultchless oyster spat on the natural bottom in the
Chesapeake Bay. It is obvious that large popula-
tions of blue crabs in our coastal waters could
completely neutralize oyster mariculture opera-
tions, especially if spat are too small when planted
or if the spat are not protected. We have planted

BLUE CRAB PREDATIONS

cultchless oyster spat of various sizes to determine
the optimum size at which to plant hatchery-
reared spat and to insure enough survival for a
positive economic return from the cost of the spat.

FIELD STUDIES

Our studies were conducted on the upper
Eastern Shore of the Maryland portion of the
Chesapeake Bay. Mean annual salinity of this
region ranges from 8 to 12 ppt. This area has no
significant populations of oyster drills, Urosalpinx
cinerea and Eupleura caudata. The most probable
predators on oyster spat in this region are the flat
worm, Stylochus ellipticus; the mud crab,
Rithropanopeus harrisii; the blue crab; and some
fish species: oyster toadfish, Opsanus tau;
croaker, Micropogon undulatus; spot, Leiostomus
xanthorus; cow-nosed ray, Rhinoptera bonasus.

Our first planting study utilized 4 1/10 acre
plots on hard sandy bottom. The bottom had very
little habitat for mud crabs or other members of
the oyster bed community. The plots were planted
with 125,000 cultchless spat in late September,
1975, each plot receiving oysters of \ :", ' : ", V
and 1" (6mm, 12 mm, 20 mm, 25 mm) in length.
The spat were produced by the Dupuy (1973)
technique, were removed from Mylar sheets when
they were about 1 1" (5 to 15 mm), and grown in
fiberglass trays in the hatchery until planted.

After two weeks on the bottom, the spat were
observed by scuba divers. All of the 6 mm spat
were missing and very little shell remained. Mor-
tality in the other plots ranged from 30 to 60 per-
cent in sample locations. By the following spring
(May 1976) no live oysters could be found. All of
the recovered shells had broken margins with
large portions of the shell missing. We thought
severe storm conditions might have tumbled the
shells on the bottom, broken the edges of the shell
and killed the oyster spat.

In 1976 ten different locations where the bottom
was protected from wave action were planted with
clutchless spat.

One such area was planted in July with
cultchless oysters ranging from 19 to 38 mm long.
Ten thousand spat were planted on a 100 sq. ft.
area marked by stakes on an active commercial
oyster bed. Within two weeks, all the clutchless
spat were dead. Blue crabs were observed to be

abundant at this location whereas mud crabs were
not found. Broken shells from the clutchless spat
were found in the planted area.

In another location, trays of cultchless oysters
ranging from 3 to 40 mm in length were placed ad-
jacent to a natural oyster bar. Half the trays had
fine-mesh wire tops, while half were unprotected.
Within one month 99.7 percent of the unprotected
cultchless spat were dead, while the protected had
no detectable mortality. The shells of the dead
spat had the same type of damage that was
observed at previous planting locations.

These are two of the most severe cases of preda-
tion we have observed but significant losses were
incurred at other planting sites even though spat
were planted in early November, 1076, after most
blue crabs had become dormant.

PATTERNS OF SHELL DAMAGE
BY THE BLUE CRABS

To confirm the hypothesis that blue crabs were
involved in the losses of oysters in the field we fed
cultchless oysters of various sizes to crabs in
aquaria. Blue crabs from 4" to 6" (100 mm to 150
mm) carapace width were found to be capable of
consuming cultchless oysters up to 40 mm in
length. Blue crabs from 65 mm to 80 mm in
carapace width were unable to consume cultchless
oysters larger that 1" (25 mm) in length.

Methods used by blue crabs to break oyster
shells vary from oyster to oyster. Small oyster
spat (3 mm to 15 mm) were simply crushed and
the meat separated from shell as the oyster was
eaten. Frequently the entire crushed oyster was in-
gested and no shell fragments could be found.

The next most common feeding strategy was to
chip the shell margin with the chelae so that the
mouth parts and chelae tips could extract the
oyster meat. Figure 1 is a scale drawing to show
this type of damage. Note that the spat shell has
very irregular edges and most of the recent shell
growth was removed, often in large chips. These
oysters look as if they had been damaged by
tumbling along a hard bottom. This was the
predominant pattern of damage observed in our
1975 bottom planting of cultchless oysters.

A characteristic of cultchless spat produced by
the Dupuy mylar technique is thinness of the shell
over the area where the lower valve of the spat

G.E. KRANTZ AND J.V. CHAMBERLIN

FIG. 1. Shells of cultchless oyster spat showing
blue crab damage to shell margins.

FIG. 2. Shells of cultchless oyster spat showing
blue crab damage to soft, flattened areas produced
on lower valves by the Mylar technique of spat
collection.

was attached to mylar. This area is easily broken
by the human fingernail and contributes to mor-
tality while handling small spat in oyster hatch-
eries. Blue crabs frequently crushed this area
(Figure 2) in their attempts to open the cultchless
oysters. Another approach was to crush the um-
bo, or hinge area (Figure 3), which then permitted
the crab to extract the oyster meat. A fairly com-
mon type of observed damage was the removal of
large chips from opposite sides of the oyster shell
as if the crab compressed the shell laterally be-
tween the digits of the chelae (Figure 4).

The most puzzling damage we observed in the
planting studies, were spat with a single round
hole in the shell (Figure 5). Up to 10 percent of the

shells in some samples had this type of damage.
Initially we thought that another predator was in-
volved in the losses of the hatchery-reared spat.
However, feeding studies in the laboratory show-
ed that blue crabs were quite effective at punching
holes. Occassionally we found shells which had
multiple holes. Figure 5 shows that the holes are
not round but are slightly irregular. Frequently the
inner shell surface of the hole and the "walls"
showed irregular fractures on the margins. The
damage differs from the more regular, smooth and
slightly conical holes made by oyster drills.

Perhaps the most important observation made
during the study was that to damage the cultchless
oyster spat all that was required was that blue

FIG. 3. Shells of cultchless oyster spat with umbo
area crushed by blue crabs.

FIG. 4. An example of chips removed by blue
crabs from opposite edges of cultchless oyster
shells.

FIG. 5. Holes punched through the shell of oyster
spat by blue crab.

BLUE CRAB PREDATIONS

crabs pick up and manipulate the oyster spat in
their claws. In this situation the edges of the
cultchless spat were accessible, in contrast to spat
on oyster shell cultch. The fragile shell edges of
cultchless oysters were easily chipped even by
small blue crabs and clutchless spat were easily
manipulated to the mouth of the crab.

Laboratory feeding studies showed that blue
crabs had much greater difficulty manipulating a
large piece of cultch to which oyster spat were at-
tached. Frequently the crab's claws were unable to
contact the spat in a manner that would damage
the shell. Manipulation to the mouth was definite-
ly impaired by cultch of any size.

MacKenzie (1970) noted that mud crabs in Con-
necticut rarely attacked an attached spat over 10
mm (about Vz in.) but they readily consumed
unattached spat up to 25 mm. His field observa-
tions were confirmed by our laboratory studies.

Our present mariculture strategy is to determine
what size of spat on various types of cultch best
survives the blue crab predation in Maryland por-
tions of Chesapeake Bay. Hopefully a combina-
tion of cultch type, size of cultch, and size of
oyster spat can be found that will reduce mortality
to a level where a positive economic return can be
realized from planting hatchery-reared spat on the
natural bay bottom.

ACKNOWLEDGEMENTS

The authors wish to acknowledge Dr. John
Dupuy for culturing some of the oysters used in
this study, Donald Meritt for assistance in field
work and for oysters he raised for the study, and
Mrs. Deborah Kennedy for her drawings of
damaged oyster spat.

This study was supported by Maryland Depart-
ment of Natural Resources Fisheries Administra-
tion.

BIBLIOGRAPHY

Castagna, M. A. , G. W. Mason, and F. C. Biggs.
1970. Hard clam culture method developed at
VIMS. Va. Inst. Mar. Sci. Sea Grant Advisory
Pgt. No. 4. 3 p.

Dupuy, J. L. 1973. Translation of Mariculture
Research into a Commercial Oyster Seed Hatch-
ery. Proc. World Mariculture Soc. 677-685.

Galtsoff, R. S. 1964. The American oyster
Crassostrea virginica Gmelin: Fishery Bulletin
No. 64. U. S. Fish & Wildlife Service, 480 p.

Lunz, G. R. Jr. 1974. Callinectes versus Ostrea, J.
Elisha Mitchell. Sci. Soc. 63: 81

MacKenzie, C. L. 1970. Causes of oyster spat
mortality, conditions of oyster setting beds, and
recommendations for oyster bed management.
Proc. Nat. Shellfish. Assoc. 60:59-67.

McDermott, J. J. 1960. The predation of oysters
and barnacles by crabs of the family Xanthidae.
Proc. Penn. Acad. Sci. 34:199-211.

McDermott, J. J. and F. B. Flower. 1952.
Preliminary studies of the common mud crabs
on oyster beds of Delaware Bay. Conv. Addr.
Nat. Shellfish Assoc. 47-50.
Menzel, R. W. and S. H. Hopkins. 1955. Crabs as
predators of oysters in Louisiana. Proc. Nat.
Shellfish Assoc. 46:177-182.

Menzel, R. W., E. W. Cake, M. L. Haines, R. E.
Martin and L. A. Olsen. 1976. Clam
Mariculture in Northwest Florida: Field Study
on Predation. Proc. Nat. Shellfish Assoc.
65:59-62.

PREDATION ON HARD CLAMS,

MERCENARIA MERCENARIA,
BY MUD CRABS, PANOPEUS HERBSTIP

Jack M. Whetstone mid
Arnold G. Eversole

DEPARTMENT OF ENTOMOLOGY AND

ECONOMIC ZOOLOGY

CLEMSON UNIVERSITY

CLEMSON, SOUTH CAROLINA 29631

ABSTRACT

Predation on hard clams planted in protected trays was studied by examination of
empty clam shells and the stomach contents of potential predators gaining entry to the
trays. Decapod crustaceans comprised 88.5% of the predators collected. Panopeus
herbstii was the most abundant species while Callinectes sapidus and Menippe
mercenaria were only occasionally found. Gastropods were collected, but examination
of empty clam shells revealed no evidence of gastropod predation. Stomach analysis
revealed clam shell bits in four crab species. Shell bits were found in 15.8% of the 279
P. herbstii analyzed. Occurrence of shell bits varied but were more often found in
stomachs of larger crabs.

The abundance and mean size of P. herbstii in trays varied from a peak in summer to
a low in winter. Clam mortalities decreased with increases in clam size and with
decreases in water temperature. Frequency of shell bits in the stomachs of P. herbstii
paralleled clam mortality. Some size selection process appeared to be operating in this
predator-prey system.

INTRODUCTION
The potential exists for improving the hard
clam, Mercenaria mercenaria, industry in South
Carolina. Rapid growth of clams, vast amounts of
suitable tidelands, increased market for southern
clams, and recent success of the Santee fishery are
some of the reasons for this optimism (Eldridge,
Waltz, Gracy and Hunt, 1976; Gracy, 1974;
Gracy and Keith, 1975). Clam mariculture has
also been demonstrated to be feasible in pilot
studies in Virginia (Castagna, Mason and Briggs,
1970), but more work remains to be done. A ma-
jor problem in culturing clams is predation. The

1 Technical contribution no. 1524, published by permission of
the Director. South Carolina Agricultural Experiment Station.

objectives of this study were to investigate preda-
tion in protected trays in an estuary in South
Carolina and to identify some important factors
influencing predation.

MATERIALS AND METHODS

Hatchery clams (X= 13 mm shell length, SL)
were planted in 20 protected oyster trays (10 inter-
tidal, 10 subtidal) containing natural sediment in
May, 1975. Basket compartments (118 x 61 x 14
cm) in the trays were enclosed with 9 mm plastic
netting and lined with fiberglass insect screens to
retain sediment. Each tray was covered with 9 mm
plastic netting to help protect against predation.
This was not completely successful because poten-
tial predators apparently could enter trays

PREDATION ON CLAMS

through the crack between the cover and basket
compartment. The trays were located near Clark
Sound, S. C. (Lat. 32° 42' 5" N, Long. 79° 52' 2"
W) in an area characterized by a soft sand
(20-30% silt-clay) bottom and a salinity range of
25-30%0atlowtide.

Fifteen collections of potential predators were
made from May, 1975 to December, 1976. All
potential predators were saved except for the col-
lections in June and July, 1975, when represen-
tative samples were taken from each tray.
Members of other feeding groups (e.g. filter
feeding polychaetes) were not collected. Field col-
lections were preserved in 10% formalin until
specimens could be sorted and counted. Crusta-
ceans were sexed and measured to the nearest 0.1
mm. The stomach contents of each crustacean
and, in most cases, all the specimens collected
were examined to determine the food types.
Samples of the abundant crustaceans, Panopeus

herbstii and the snapping shrimp (Alpheus spp.),
were selected for examination. Samples of P. herb-
stii included representatives from each sample
date, tidal location, and three class intervals of
carapace widths (CW): small crabs <15 mm CW;
medium crabs 15.1-25.0 mm CW; and large crabs
>25 mm CW. Cardiac stomachs were excised,
and the individual food items were sorted as clam
shell bits, arthropod parts, plant material and grit.
Finely ground food items which could not be iden-
tified and sediment were classified as grit. The fre-
quency of each food item was expressed as percent
occurrence in individuals containing food. The
quantity of a food item was estimated by the
points' method (Hynes, 1950).

Clam growth and mortality in each tray was
determined during the sampling period. Clam den-
sity was maintained in the individual trays by
replacing dead or sacrificed clams with marked
clams of comparable size. Empty clam shells were

TABLE 1. Potential predators collected from
centages represent totals for 15 sampling dates
in stomachs is represented by + ; the absence 0

20 protected trays containing clams. Numbers and per-
from 5/75 through 12/76. The presence of clam shell bits
and not examined ne.

Presence

% of

%of

Clam Shell

Number

Order

Class

Total

Bits

CRUSTACEA
Decapoda
Panopeus herbstii
Callinectes sapidus
Menippe mercenaria
Eurypanopeus depressus
Neopanope texana
Uca pugilator
Eurytium limosum
Pachygrapsus transversus
Alpheus heterochaelis
Alpheus armillatus
Alpheus normanni
Stomatopoda
Squilla empusa
GASTROPODA
Neogastropoda
Urosalpinx cinerea
Nassarius vibex
Nassarius obsoleta
Eupleura caudata
TOTAL

1746

—

100.0

88.9

1740

100.0

99.7

88.5

1465

84.2

83.9

74.6

0.5

0.4

0.5

0.4

0.7

0.1

0.5

0.1

184

10.6

10.5

9.4

2.2

2.0

0.5

100.0

0.3

100.0

0.3

219

—

100.0

11.1

219

100.0

11.1

150

68.5

7.6

4.6

0.5

25.6

2.8

1.4

0.2

1965

J.M. WHETSTONE AND A.G. EVERSOLE

collected to determine the size of dead clams and
possible cause of mortality. Materials and
methods not detailed above were described
previously (Eldridge et al., 1976).

RESULTS

The number of potential predators found in the
trays are presented in Table 1. P. herbstii, a mud
crab, was the most abundant (75%) species col-
lected. Predators of clams which are generally
suspected, Callinectes sapidus and Menippe
mercenaria, comprised less than 1% of the
specimens found. Gastropods were common, but
empty clam shells did not exhibit the borehole
characteristic of gastropod predation. Cracked
and crushed clam shells were abundant in the
trays indicating forced entry, probably by crusta-
ceans.

Fourteen percent of the 362 crustaceans ex-
amined contained clam shell bits in their cardiac
stomachs. Only four species (i.e., P. herbstii, C.
sapidus, Menippe mercenaria and Eurypanopeus
depressus) of the 12 species of crustaceans ex-
amined contained shell bits (Table 2). There was
no significant difference (PX3.05) between the oc-
currence of shell bits in the four species.

Clam shell bits were more frequent in stomachs
of large crabs (Table 2). Shell bits were found in
significantly greater (P<0.05) percentage of large
P. herbstii than were found in medium and small
ones. Although percent occurrence of shell bits in
P. herbstii were significantly different between
sizes, volumes (i.e. point method) were not.
Variation in this trend among the less abundant
species can be accounted for by the number and
temporal differences of the crab populations in the
trays. No shell bits were observed in medium-
sized E. depressus (15.1-25.0 mm CW), however
crabs this size were absent until May, 1976 when
clams had a 36.6 mm mean shell length. Small
sample sizes also limited statistical analyses of
data on the less abundant species.

Prey size, as well as predator size, apparently
affects clam mortality levels. The mean shell
lengths (SL in mm) of live and dead clams (i.e.
empty shells) increased linearly after time of plant-
ing (x = time in months). The regressions are:

live clams x SL = 1.69x + 4.76; and

dead clams x SL = 1.31x + 3.37,

with r values of 0.99 and 0.96 respectively. These
linear regressions are significantly different

TABLE 2. Analysis of crab stomach contents containing clam shell bits. Percent occurrence is based on
those crabs with food. Crab size class intervals are small < 25.0 mm carapace width (CW), medium
15.1-25.0 mm CW and large > 25.0 mm CW.

Carapace

Number

Clam

% Occurrence

Crab Species Width

Examined

Food

Shells

Arthropods

Plants

Grit

Panopeus herbstii Small

76.1

10.0

20.0

44.3

100.0

Medium

119

87.4

15.4

18.3

38.5

100.0

Large

97.1

31.8

43.9

100.0

Total

279

86.0

18.3

22.5

41.7

100.0

Callinectes sapidus Small

100.0

33.3

100.0

Medium

100.0

Large

100.0

50.0

25.0

100.0

Total

100.0

25.0

100.0

Menippe mercenaria Small

71.4

20.0

40.0

20.0

100.0

Large

100.0

Total

75.0

33.3

16.7

100.0

Eurypanopeus depressus Small

100.0

25.0

50.0

100.0

Medium

83.3

40.0

100.0

Large

100.0

66.7

33.3

66.7

100.0

Total

92.3

25.0

8.3

50.0

100.0

PREDATION ON CLAMS

50.

% 40J
WITH
CLAM
SHELLS

20.

LJ Large Crabs 0250mm)
(ZI Medium Crabs( 15 I -250mm)
Ul Small Crabs(il5.0mm)

A S
1975

0 N D

J F

M A M J J A

97«

S 0 N D

FIGURE 1. Percent P. herbstii containing food with clam shell bits plotted against sampling month. At
any date the percentage of crabs containing food with shell bits is represented by the entire histogram.
Representatives of each size class interval were found in all collections except 6/75 when no large crabs
were found.

(P<0.01) suggesting clam size as an integral com-
ponent of predation. As clam size increased the
percentage of P. herbstii containing clam shell bits
decreased (Figure 1). Also the proportion of large
P. herbstii with shell bits increased from 40% in
1975 to 67% in 1976. Only large P. herbstii con-
tained shell bits one year after planting. Over the
same period, mortality of clams decreased from a
high of 30.2% to a relatively constant low mor-
tality of approximately 0.5% per month by
March, 1976. (Figure 2).

The abundance and mean size of P. herbstii
varied throughout the experimental period (Figure
3). This variation could be due to several cohorts

in the crab population. The mean size of crabs was
greatest in the warmer months (i.e. June - Oc-
tober). Laboratory observations indicate that in P.
herbstii 20.0 mm CW was the minimum size
necessary for successful predation upon clams
above 11.5 mm SL (the approximate planting
size). The percentage of the crab population above
this minimum successful predator size changed
significantly (P<0.05) throughout the year with
the greatest percentage in the summer (i.e. June,
July, and August). Also the average number of P.
herbstii above 20 mm CW was significantly
(P<0.05) greater during the summer than fall,
winter and spring. This seasonal variation of P.

J.M. WHETSTONE AND A.G. EVERSOLE

jIjIaIsIoInId

1975

' 2
2

20£

I0IX

JlFlMlAlMlJ |J lAlSlOlNlO
1976

FIGURE 2. Percent mortality of clams and mean shell length of live clams grown in 20 protected trays
plotted against sampling date. (P. ]. Eldridge and A. G. Eversole, unpublished data).

herbstii allows speculation into some methods of
predator control.

DISCUSSION
Callinectes sapidus, Carcinus maenas, and
Menippe mercenaria have been documented as
major predators of the hard clam, Mercenaria
mercenaria (Belding, 1912; Carriker, 1951; God-
win, 1968; Haven and Andrews, 1957; Loosanoff,
1946; Menzel, Cake, Haines, Martin and Olsen,
1976; Menzel and Sims, 1962). Callinectes sapidus
and Menippe mercenaria have been suspected of
causing 100% mortality in hard clams planted in
unprotected plots in Georgia and Florida (God-
win, 1968; Menzel and Sims, 1962). Haven and
Andrews (1957) reported C. sapidus as the major
predator of hard clams planted in suspended trays
in Virginia. Other decapods have been proposed
as predators of hard clams. Eldridge et al. (1976)
suggested mud crabs, members of the Xanthidae

family, were important predators of clams in
South Carolina.

Callinectes sapidus and Menippe mercenaria
comprised less than 1% of the potential predators
collected and could not be the major cause of mor-
tality in our culture system. Clam shell bits were
found in only four species of predators, three of
which were xanthid crabs. The xanthid crab, P.
herbstii. appeared to be the most important
predator in this system. To date no specific men-
tion has been made of P. herbstii as a predator of
the hard clam, although McDermott (1960) cited a
predator-prey interaction between P. herbstii and
Crassostrea virginica. Carriker (1959) and Landers
(1954* also cited Neopanope texana. a xanthid
crab, as an effective predator of seed clams.

Prey and predator size appear to be major fac-
tors in the Panopeus herbstii - Mercenaria
mercenaria interaction. Menzel and Hopkins

PREDATION ON CLAMS

(1956) observed that the size of the Menippe
mercenaria limits this xanthid crabs ability to
prey on oysters. Our findings indicate that larger
P. herbstii preyed more successfully on clams
than smaller crabs. Also, the proportion of small
and medium crabs containing clam shell bits
decreased as clam size increased. A major decline
in mortality was observed as clams grew larger,
and the percent of P. herbstii containing shell bits
declined from 50% when clams averaged 15.5 mm
SL to less than 5% after clams reached an average
size of 38.4 mm SL. Carriker (1959) observed that
a larger initial planting size significantly reduced
mortality of clams in unprotected plots. Assuming
that predatory activity of P. herbstii was limited
by clam size, planting larger clams should reduce
mortalities.

Crabs may be selecting the smaller clams in the
trays. The regression for mean shell lengths of live
clams against time (months) was significantly
greater than the regression for the mean shell
lengths of dead clams. Furthermore this regression
for live clams was significantly greater than a
regression representing the projected sizes of dead
clams if the dead clams had the opportunity to
grow throughout each sampling interval. The pro-
jected size was computed by adding the mean shell
length of dead clams and an increment equivalent
to shell growth of live clams for the appropriate
sampling interval. McDermott (1960) suspected
that P. herbstii selected thinner-shelled oysters.
Cake (1970) found no prey size selectivity by C.
sapidus and Menippe mercenaria when offered
sunray venus clams, Macrocallista nimbosa.
Smaller species of crabs may not have the ability
to open the larger and /or thicker-shelled molluscs.
Smaller species of crabs such as P. herbstii may
therefore exhibit more prey size selection than
larger crab species. If the larger crabs are more
capable of preying on a wide variety of clam sizes
or thicknesses, then prey size selectivity probably
will not be pronounced. This may explain, in part,
why Cake (1970) observed no size selectivity with
C. sapidus and Menippe mercenaria.

Menzel and Hopkins (1956) found lower mor-
talities in oysters in Louisiana during the winter,
and predation by Menippe mercenaria was not
observed below 10 °C. Similarly we observed
lower mortalities in the winter months when water

%
S

-14

j 1 j Ia Is lo In lo jIfImIaImIjIjuIsIoInId
1973 1976

FIGURE 3. Smoothed means of carapace widths
(in mm) of P. herbstii from trays plotted against
mean sampling dates. Histograms show percen-
tages of sampled crabs with carapace widths larger
than 20 mm.

temperatures approached 8°C. Less activity by the
crabs in the winter would contribute to this lower
observed mortality. Lower mortality also cor-
responded to the presence of fewer P. herbstii and
a smaller percentage above the minimum effective
predator size during winter.

Time of planting and clam size should be con-
sidered in formulating any management program
for extensive clam culture operations. Planting
clams in the late fall should improve survival of
seed because predator populations are then at
lower levels. Also, there are fewer large predators,
and predators are generally less active during
cooler months. In addition, during this period
clams have an opportunity to grow to a size that

J.M. WHETSTONE AND A.G. EVERSOLE

will limit predation by the smaller crabs. If
selected planting times and clam sizes were used
with other techniques such as aggregate protection
to effectively reduce predation, clam culture can
be successful and profitable even in areas where
predators abound.

ACKNOWLEDGEMENTS
The senior author wishes to thank Drs. P. J.
Eldridge (South Carolina Wildlife and Marine
Resources Department) and A. G. Eversole for the
unpublished data on clam growth and mortality.
Special thanks are also due Wayne Waltz and
George Steele for their assistance in field collec-
tions.

LITERATURE CITED

Belding, D. L. 1912. The quahog fishery of
Massachusetts. Comm. Mass. Dept. Conserv.
Mar. Fish. 2:1-41.

Cake, E. W., Jr. 1970. Some predator-prey rela-
tionships involving the sunray venus clam,
Macrocallista nimbosa (Lightfoot) (Pelecypoda:
Veneridae) along the gulf coast of Florida. M.S.
Thesis, Florida State University, Tallahassee,
Florida, 169 pp.

Carriker, M. R. 1951. Observations on the
penetration of tightly closing bivalves by
Busy con and other predators. Ecology 32:73-83.

Carriker, M. R. 1959. The role of physical and
biological factors in the culture of Crassostrea
and Mercenaria in a salt-water pond. Ecol.
Monogr. 29:219-266.

Castagna, M. A., L. W. Mason and F. C. Briggs.
1970. Hard clam culture method developed at
VIMS. Va. Inst. Mar. Sci., Sea Grant Advisory
Ser. No 4, 3 pp.

Eldridge, P. J., W. Waltz, R. C. Gracy and H. H.
Hunt. 1976. Growth and mortality rates of
hatchery seed clams, Mercenaria mercenaria, in
protected trays in waters of South Carolina.
Proc. Natl. Shellfish. Assoc. 66:13-20.

Godwin, W. F. 1968. The growth and survival of
planted clams, Mercenaria mercenaria, on the

Georgia coast. Georgia Game and Fish. Comm.
Contrib. Ser. 9:1-16.

Gracy, R. C. 1974. Management and development
of the shellfish industry in South Carolina.
Ann. Rept. on Project 2-179-D in Coop, with
Natl. Mar. Fish. Sen/., Dept. of Commerce.
Under Public Law 88-309, 22 pp.

Gracy, R. C. and W. J. Keith. 1975. Management
and development of the shellfish industry in
South Carolina. Final Rept. on Project 2- 179-D
in Coop, with Natl. Mar. Fish. Serv., Dept of
Commerce. Under Public Law 88-309, 110 pp.

Haven, D. and J. D. Andrews. 1957. Survival and
growth of Venus mercenaria, Venus campech-
iensis. and their hybrids in suspended trays and
on natural bottoms. Proc. Natl. Shellfish.
Assoc. 47:43-49.

Hynes, H. B. N. 1950. The food of fresh-water
sticklebacks (Gasterosteus aculeatus and Pyg-
osteus pungitius). with a review of methods us-
ed in studies of the food of fishes. J. Anim. Ecol.
19:36-58.

Landers, W. S. 1954. Notes on the predation of
the hard clam. Venus mercenaria, by the mud
crab, Neopanope texana. Ecology 35:422.

Loosanoff, V. L. 1946. Commercial clams of the
Atlantic Coast of the United States. U. S. Fish
Wildlife Service Leaflet 13:1-13.

McDermott, J. J. 1960. The predation of oysters
and barnacles by crabs of the family Xanthidae.
Proc. Pa. Acad. Sci. 34:199-211.

Menzel, R. W., E. W. Cake, M. L. Haines, R. E.
Martin, and L. A. Olsen. 1976. Clam
mariculture in Northwest Florida: Field study
on predation. Proc. Natl. Shellfish. Assoc.
65:59-62.

Menzel, R. W. and S. H. Hopkins. 1956. Crabs as
predators of oysters in Louisana. Proc. Natl.
Shellfish. Assoc. 46:177-184.

Menzel, R. W. and H. W. Sims. 1962. Experimen-
tal farming of hard clams, Mercenaria
mercenaria in Florida. Proc. Natl. Shellfish.
Assoc. 53:103-109.

Proceedings of the National Shellfisheries Association
Volume 68-1978

SEASONAL ASPECTS OF THE BIOLOGY, DISTRIBUTION AND

RELATIVE ABUNDANCE OF THE DEEP-SEA RED CRAB

GERYON QUINQUEDENS SMITH, IN THE VICINITY OF THE

NORFOLK CANYON, WESTERN NORTH ATLANTIC1,2

Paul A. Haefner, Jr.3

VIRGINIA INSTITUTE OF MARINE SCIENCE
GLOUCESTER POINT, VIRGINIA 23062

ABSTRACT

Deep-sea red crabs were collected from demersal trawl surveys of Norfolk Canyon
and an adjacent open slope area in the Chesapeake Bight of the western North Atlantic
Ocean. The surveys were made in each of four seasons over a period of three years.
The 2539 red crabs caught ranged from 16mm to 143 mm in carapace length (CL). Rela-
tionships between CL and carapace width (CW) were derived for 308 males and for 269
females. Wet weight to CL relationships were derived for 238 males and for 142
females.

Red crabs were contagiously distributed within the total depth range of capture (200-
1800m) as well as within the 300-1000 m range of most consistent catches. They were
equally abundant in canyon and slope regions in the four seasons. The majority of the
population inhabits bottom water deeper than 400 m arid overlain by cold, well-
oxygenated water.

Over 50% of all red crabs were larger than 96 mm CL (114 mm CW), the minimum
size presently acceptable to processing plants. This proportion varied by sex, season
and depth. Potentailly marketable male crabs constituted 70% of total males caught,
whereas less than 25% of females exceeded 96 mm CL. Seasonally the proportions were
consistent for males, but varied for females. The proportion of large males was consis-
tent over most of the depth range (200-1600 m). Most of the larger females were cap-
tured in water shallower than 600 m.

An inverse relationship between water depth and crab size was evident for females
from 200-1500 m; for males only in the 200-500 m depth range. The mean size of males
caught deeper than 600 m was fairly stable.

Females were more abundant than males in samples shallower than 600 m: males
dominated catches in deeper water.

A spawning cycle is suggested although ovigerous females were captured in all
seaons. Peak incidence of ovigerous females occurs in November characterized by a
high percentage of late stage eggs and a peak incidence of recently extruded eggs. The

Research cruises supported by National Science Foundation Grant GA-37561, J. A. Musick. principal investigator, by the
University of Virginia Institutional Grant Program; and NOAA, Office of Sea Grant (NO. 04-3-158-49) tor P.A.H. participation.

Contribution No. 830, Virginia Institute of Marine Science.

Present Address: Department of Biology, Rochester Institute of Technology, Rochester, New York 14623.

P. A. HAEFNER, JR.

ovarian cycle of non-ovigerous females complements the spawning pattern. From June
through November, an increase in incidence of developing ovaries urns accompanied
by a decrease in advanced and mature ovaries. Absence of mature ovaries in
November complements the peak incidence of ovigerous females at that time.

Relative density of red crabs was estimated for the Norfolk Canyon area and com-
pared with values from other areas along the east coast of the United States.

INTRODUCTION

Interest in Geryon quinquedens Smith as a
marketable species has been slowly increasing. In-
itial explorations (Schroeder 1959; McRae 1961)
proved that red crabs were readily captured with
trawls off the east coast of the United States. More
recent surveys have been concerned with
estimating fishery potential and evaluating
harvesting methods, both in the United States
(Gray4; Haefner and Musick, 1974; Ganz and Her-
rman5; Wigley, Theroux and Murray, 1975) and
in Africa (Dias and Machado6; LeLoeuff, Intes and
LeGuen, 1974; Intes and LeLoeuff, 1976)
Technological and economic aspects of harvesting
have also been under investigation (Varga, Dewar
and Anderson, 1969; Meade and Gray, 1973;
Holmsen and McAllister, 1974)

Other than the data obtained by Haefner and
Musick (1974) and Wigley, et al. (1975), which
were restricted to one period of sampling, obser-
vations on the biology of Geryon have been super-
ficial. This paper supplements the survey of
Haefner and Musick (1974) by presenting seasonal
data on distribution, relative abundance and
reproductive biology of red crabs in the
Chesapeake Bight area of the western North
Atlantic Ocean.

MATERIALS AND METHODS
Deep-sea red crabs were collected during demer-
sal fish trawl surveys of Norfolk Canyon and an

4 Gray, G. W., Jr. 1969, Investigation of the basic life history
of the red crab (Geryon quinquedens). Rhode Island Div.
Cons. Completion Rep. (P.L. 88-309, Proj. 3-46-R), pp.36.

s Ganz, A. R. and J. F. Hermann, 1975. Investigations into the
southern New England red crab fishery. Rhode Island Dept.
Nat. Res. Div. Fish. Wild]. Mar. Fish. Sec. pp. 78.

6 Dias, C. A. and J. F. S. Machado. 1974. Preliminary report
on the distribution and relative abundance of deep-sea red
crab (Geryon sp.) off Angola, 8 p. In: Scientific papers pre-
sented to the second session of the International Commis-
sion for the Southeast Atlantic Fisheries (Madrid, December
1973), M. E. Bioceanol. Pescas, Angola, 12, pp. 75.

adjacent open slope area in the Chesapeake Bight
region of the western North Atlantic Ocean
(Figure 1.) Four surveys, one in each season, were
made during a period of three years using Univer-
sity of Miami vessels R/V Columbus O. Iselin and
fames M. Gilliss (Table 1). The sampling gear con-
sisted of 15.1 m (headrope) semi-balloon, 4- seam
shrimp trawls equipped with plastic mud- rollers
and steel China V-doors. The nets were nylon of
the following stretch mesh: 44 mm body, 37 mm
intermediate, 36 mm codend and 12 mm inner
liner. Thirty-minute tows were made in depth
strata less than 1000 m; tow time was one hour at
deeper stations.

Initially, an equal number of tows was to have
been made in each of four depth strata (75-150 m,
150-400 m, 400-1000 m, 1000-2000 m) in the can-
yon and slope areas. Variations in actual depth of
tows, encounters with bottom types prohibitive to
trawling and cruise time limitations combined to
alter the program. The realized effort is presented
in Table 1. Mean trawl depths were calculated
from depths recorded at start and finish and at 3-
minute intervals during each tow.

All red crabs were processed at sea. Carapace
width (CW, distance between the tips of the lateral
spines) and carapace length (CL, distance from the
diastema between the rostral teeth to the posterior
edge of the carapace, along the midline) were
measured to the nearest millimeter. The latter
measurement was emphasized based on recom-
mendations of Gray". Accuracy in weighing,
which was done aboard ship, depended on sea
state conditions. In most cases, weight was record-
ed to the nearest gram; some larger specimens
were weighed to the nearest decigram.

Females were examined for evidence of egg ex-
trusion and hatching. Color of eggs was noted for
most females. External eggs from selected
ovigerous females were examined microscopically
to relate developmental stage to egg color.
Developmental stages of ovaries of selected non-

SEASONAL DEEP-SEA RED CRAB

76c

75<

74'

73c

38c

37c

36°

76°

75°

74c

38c

37<

36<

73c

FIGURE 1. Chart of the Cheapeake Bight region of the western North Atlantic region showing shelf (SH),
canyon (C) and open slope (S) trawl survey areas in the vicinity of the Norfolk Canyon. Isobaths in
fathoms.

ovigerous females were classified as described in
Haefner (1977).

Temperature and salinity of near-bottom water
strata were monitored at trawl stations as well as
at independent hydrographic stations. A variety
of instruments was used including bathyther-
mographs, expendable bathythermographs, a
salinity-temperature depth recorder and reversing
thermometers. Dissolved oxygen concentration of
near-bottom water samples was determined by
Winkler titration.

RESULTS AND DISCUSSION

Profiles of near-bottom (within 5-100 m of
recorded depth) temperature and dissolved ox-
ygen concentration (D.O.) for the four cruises are

presented in Figure 2. In all cases the data for can-
yon and slope areas are combined. The June plot
reflects only data taken in conjunction with trawl
stations; the other three plots include data from
hydrographic and trawl stations. Only data from
stations shallower than 1600 m are included.

Throughout the year temperature of near- bot-
tom water was indirectly proportional to depth at
depths exceeding 100 m (Figure 2). A large
temperature gradient from 13 °C to 6 °C existed
between 100 and 500 m. Below 500 m,
temperature decreased gradually to 4° C at 1600
m.

Oxygen minima were associated with the ther-
mal gradient (Figure 2). They were particularly
obvious in June and November when D.O. values

P. A. HAEFNER, JR.

TABLE 1. Norfolk Canyon demersal trawl fishing effort, expressed as number of tows, in the ca)iyon (C)
and on adjacent open slope (S) by season and by depth strata between 200 m and 1800 m.

Depth

Stratum

(m)

Spring Summer Fall Winter

4-16 June 73 9-20 September 75 13-25 November 74 22-31 January 76
QS CS CS CS

201- 300
301- 400

401-
501-
601-

701-
801-

500
600
700
800
900

901-1000
1001-1200
1201-1400
1401-1600
1601-1800

TOTAL

of 4.6 mg/liter were detected in near-bottom
water within the 200-400 m depth range. Between
400 m and 800 m D.O. increased to 8 mg 'liter,
which persisted to a depth of 1600 m.

Except for shelf stations shallower than 200 m,
salinity of near-bottom water was consistently
between 35 % and 36 % .

The 2539 red crabs caught during these cruises
ranged from lb mm to 143 mm in carapace lenth
(CL). For purposes of comparing carapace length
with carapace width (CW) reported in other
papers, the following relationships were derived
for 308 males, CL range 18-138 mm:

CW = 8.74 + 1.09 CL, r = 0.98
and for the 269 females, CL range 23-116 mm:
CW = 11.04 + 1.0b CL, r = 0.98

Male crabs attain a larger size than females. The
largest male crab caught measured 143 mm CL
and weighed 1200 g; the largest female was 123
mm CL and weighed 510 g. The following wet
weight- length relationships were derived for 238
males ranging from 3 g to 1200 g:

log male weight = -3.58 + 3.14 log CL,
r = 0.99 and for 142 females ranging from 4 g to
510 g:

log female weight = -3.13 + 2.88 log CL,
r = 0.97.

Although the size frequency distributions
(Figure 3) indicate that the red crab is obviously
not vulnerable to the trawl gear, certain modal
groups (CL) were recognized in nearly every
season. The most obvious were the 90-130 mm
group for males and the 75-110 mm group for
females. Other modal groups, such as 50-90 mm
for males and 50-75 mm for females were less ob-
vious. Wigley, Theroux and Murray (1975), in a
survey extending from offshore Maryland north-
eastward to Corsair Canyon on Georges Bank,
observed similar modal groups for male crabs.
Their female size frequency curve, however, did
not indicate a well-defined intermediate group.
On the other hand, their well-defined peak for red
crabs less than 30 mm CL was missing from Nor-
folk Canyon samples.

Analysis of the Norfolk Canyon data using a
three-point moving average, with subsequent
calculation and plotting of percent cumulative fre-
quency on probability paper was encouraging.
Thirteen to fifteen smaller, less pronounced modes
were detected which suggest molt classes within
the larger modal groups. If, indeed, the smaller
modes were representative of molt classes, a 6 to
11 percent range in growth increment (CL) is sug-
gested. This range is comparable to four of the five

SEASONAL DEEP-SEA RED CRAB

TEMPERATURE (C) AND DISSOLVED OXYGEN (rug/liter)
4 6 6 10 12 14 16 .4 6 6 10 12 14

LONG CARAPACE WIDTH (mm)

FIGURE 2. Seasonal profiles of temperature (T)
and dissolved oxygen (D.O.) of near-bottom
water in relation to depth in the Norfolk Canyon
and adjacent shelf and slope area.

observations (6.7, 8.5, 8.9, 10.4, 18.1%) of Gray4
of crabs molting in the laboratory. One red crab
molting at VIMS increased in length by 13.8%.

FIGURE 3. Seasonal size frequency distributions
of Geryon quinquedens. Males are plotted above
the line; females below. Black areas indicate
ovigerous individuals and those with egg rem-
nants on the pleopods.

Vertical arrows indicate present acceptable
market size. Scales for carapace length and
carapace width are included for comparative pur-
poses.

Crabs less than 70 mm CL were poorly
represented in the June sample (3% of the catch),
but they made up an increasingly larger propor-
tion of the catch through September (13.8%) and
November (22.9%). The proportion in January
(16.4%) was largely due to the absence of crabs
less than 50 mm CL.

Over 50% of all Norfolk Canyon red crabs were
larger than 96 CL (114 mm CW), the minimum
size presently acceptable to processing plants
(Wigley, Theroux and Murray, 1975). This pro-
portion varied by sex, season and depth (Table 2).

P. A. HAEFNER, JR.

o»

«*'

^i"

r-i

>,
-G

PL,

—

— i

—

t-^.

r-4

r-)

O
H

t~^

•£

r 1

t-H

"^3

,—i

r-t

•^<

T—t

-c

tX)

>-■

PL,

T-*

CnJ

1<
00

nO
Pn)

1 ■

"3"

1"H

r-i

'S'

i — i

"-1

a
a

I V

■t

PL,

r-4

^1"

^t"

t— 1

— 1

r—i

T~i

r~t

r~*

K
0)

r—*

^-*

rs]

S3.

■*

■f

T-

UL,

!-H

r 1

r-*

— I

■*

'S1

"bo
3

r-<

^Oj

r-(

T—t

— ■

-a
i>

■^<

rr>

■3"

r-l

Ctf

'3
a*

■*

T—t

r-4

■^

t>!

— i

T—l

^—<

-a

—

-r

[ V

-r

_CJ

r-<

T—4

—

r~*

-T

■*

r-i

r-<

—

Potentially marketable male crabs constituted
70% of total males caught whereas less than 25%
of the females exceeded 96 mm CL, a reflection of
the larger ultimate size of male crabs. Seasonally,
the proportions were consistent for males, but
varied for females. A high proportion of females
(39%) in June reflected the absence of small modal
groups at that time; a low of 7.4% in November
was related to a reduced modal group of large
females.

These figures are markedly higher than the
percentage (24%) of harvestable crabs in the
northeast red crab survey (Wigley, Theroux and
Murray, 1975). However, any comparisons bet-
ween the two geographic areas must be qualified.
Differences in size frequency distributions of the
two populations are most likely related to the dif-
ferences in sampling methods.

Comparison with other geographic regions is
further complicated by difference in the acceptable
harvestable size as well as in method of catch. For
example, the minimum size of red crabs for the
Ivory Coast of Africa is 84 mm CL (100 mmCW)
(Intes and LeLeouff, 1976). In their survey 70% of
the total catch of red crabs (38% of all males) was
legal. If 84 mm CI instead of 96 mm CI was the ac-
cepted minimum market size in the Untied States,
the percentage of potentially marketable male
crabs caught in the Norfolk Canyon survey would
increase from 70% to 78% and the percentage of
marketable females would increase from 50% to
65%.

The proportion of large males in the population
was consistent over most of the depth range
(Table 2). Most of the larger females were found in
relatively shallow water, <600 m.

The inverse relationship between water depth
and crab size observed by Wigley, Theroux and
Murray (1975) was also evident for females from
200 m to 1500 m and for males only in the 200-500
m depth range in the Norfolk Canyon region
(Figure 4). The mean size of male crabs caught
deeper than 600 m was fairly constant. Apparent
seasonal variations shown in Figure 4 are due to
lack of samples (Table 1) and/or low number of
specimens in certain depth strata.

Red crabs were contagiously distributed within
the Norfolk Canyon survey area within the total
depth range of capture (220-1800 m), as well as
within the 300-1000 m range of most consistent

SEASONAL DEEP-SEA RED CRAB

I40t

I30--

I20--

<s>

£ iio-

Q.
<

<
a.
<

<
O

100
90 -
80--

100
90

o 80

70--

60-

50-

MALE

200

DEPTH (m)

FEMALE

X
o

200 400 600 800 1000

DEPTH (m)

1200

1400

400 600 800 1000 1200 1400 1600

--I60

-150 "g

E
--I40 -*

-130 q

--I20
ui
o

--no <

Q.
<

■-100$
o

110

M00 E

-90

--80

+ 70 <

Q-
<

cr
<

1600

FIGURE 4.
and for all
poses.

Geryon quinquedens. Relation of mean size of males and females to depth according to season
seasons combimed. Scales for carapace length and width are included for comparative pur-

catches. Because there was an excess of samples
with zero catch and the variance exceeded the
mean number of crabs per tow (X= 23.3 within
200-1800 m; X= 39.5 within 300-1000 m), catch
data were transformed (Elliott, 1971) as an index
of abundance: Y = "M'4|> where x is the

number of red crabs caught per 30 minute tow in
any given stratum and n is the number of tows at
any given depth. Data from the hour long tows
were adjusted to correspond to half hour tows.

Red crabs were significantly (P = 0.001) more
abundant on the adjacent slop than in Norfolk
Canyon proper (Figure 5). Although stratifying
depth by 100 m and 200 m intervals emphasizes
voids in actual sampling depth (Table 1), it is evi-
dent that the distributional depth range is broad,
from 200 to 1800 m (actual fishing depth range
was 210 m to 1725 m). Most hauls were successful
in catching crabs within the 400-1000 m zone (ac-
tual fishing depth 405 m to 1042 m) where relative

P. A. HAEFNER, JR.

B i

2/5 "-

3/ o

1/1

-B-£-

37/52

301- 401- 501- 601- 701- 801- 901- 1001- 1201- 1401- 1601- j

300 400 500 600 700 800 900 1000 1200 1400 1600 1800
DEPTH (m)

FIGURE 5. Relative abundance of Geryon quin-
quedens by area, expressed as index of trans-
formed mean number of crabs per half-hour tow
within each depth stratum. Fraction above or
below each bar is the ratio of the number of sta-
tions at which red crabs were captured to the total
number of stations in each stratum.

abundance was highest. The actual distributional
depth range is most likely 210-1565 m because the
single individual recorded for the 1601-1800 m
stratum is suspected to be a wash-down from a
previous sample.

In light of the temperature-dissolved oxygen-
depth relationship, it is clear that the majority of
the red crab population inhabits bottom waters
deeper than 400 m which are overlain by cold,
well-oxygenated water (Figures 2,5). A smaller
percentage of tows caught crabs in the shallower
«400 m) areas where warmer, oxygen minimum
water existed.

Females were more abundant than males in
samples from depths shallower than 600 m; males
dominated the catches in deeper water (Figures
6,7H). This segregation of the sexes by depth has

CANYON AND SLOPE

201- 301- 401- 501- 601- 701- 801- 901- 1001- 1201- 1401- 1601-

300 400 500 600 700 800 900 1000 1200 1400 1600 1800

DEPTH (m)

FIGURE 6. Relative abundance of Geryon quin-
quedens by sex, expressed as index of transformed
mean number of crabs per half-hour tow within
each depth stratum.

been observed in other areas. In Rhode Island
waters Ganz and Herrman (1975) observed a lack
of females between 700 m and 915 m; the greatest
percentage of males was caught in 685-1110 m.
The survey of Wigley, Theroux and Murray
(1975) indicated a marked reduction of the
number of females in water deeper than 500 m,
where males predominated. Basicallly the same
pattern was observed off the coasts of Angola

CARAPACE WIDTH (mm)
20 40 60 80 100120 140 160 170

CARAPACE WIDTH (mm)
20 40 60 80 100 120 140 160 1 70

100

TOTAL

"*\ /SEPTEMBER

20 40 60 80 100 120 140 160 20 40 60 80 100 120 140 160

.- '00

60-

CANY0N U> 40

< 20

"\ / N0VEMB

20 40 60 80 100 120 140 I60K 20 40 60 80 100 120 140 160

\ / SLOPE

SIUU1

£80-

O- 60-

/ JANUARY

20-

20 40 60 80 100 120 140 160 20 40 60 80 100 120 140 160

CARAPACE LENGTH (mm)

DEPTH (m)

FIGURE 7. Percentage of Male Geryon quin-
quedens by size and depth. Data expressed as
probability curves for total catch, area, season
and depth. Scales for carapace length and width
are included for comparative purposes.

(Dias and Machado") and Abidjan (Ivory Coast)
(LeLoeuff, Intes and LeGuen, 1974; Intes and
LeLoeuff, 1976): the largest male catch was
recorded from 600-700m; females were largely
restricted to 300-400 m. A 400-600 m zone of tran-
sition was recognized wherein males and females
occurred in variable, but nearly equal numbers.

The combined, four-cruise male: female ratio
was 1.28:1, significantly different from the

SEASONAL DEEP-SEA RED CRAB

theoretical 1:1 (Chi-Square, P = 0.01). The ratio
varied from cruise to cruise with significant dif-
ferences (M:F) in September (1.77:1), November
2.51:1) and June (0.73:1). The 0.88:1 ratio in
January was not significant.

The presentation of sex ratio data in the form of
probability curves (Wenner, 1972) is more mean-
ingful. Red crab data were tabulated into 10 mm
size classes and the sex ratio (as percent males)
calculated within each class and plotted. The
"anomalous" pattern shown for total red crab
catch (Figure 7A) is not appreciably different than
that for location (Figure 7B, C) or season (Figure
7D-G). Scatter about the curves is due to low
numbers of individuals in the smaller size classes.
The "anomalous" pattern is consistent with the
Fisher theory (Wenner, 1972) in which a 1:1 off-
spring production is favored by natural selection,
but a unique deviation from the 1:1 ratio is il-
lustrated for older or larger animals.

The observed pattern is principally a function of
physical size. The shape of the curve for red crabs
exceeding 100 m CL is determined by the larger
maximum size of male crabs. Although growth
rate and longevity are presently unknown for
Geryon, it is known that females reach maturity at
65-75 mm CL, (Haefner, 1977) and continue to
molt to eventually attain at least 116 mm CL.
Males most likely reach maturity near 65-75 mm
CL but attain a larger maximum size than females,
either by more frequent molts, larger molt in-
crements, living longer or by a combination
thereof.

The paucity of males and an accumulation of
females distributed about 85 mm CL (Figure 3)
shows up as a dip in the probability curve. The ac-
cumulation of females in the large modal size
group bracketing 85 mm CL could be due to
longer intermolt intervals, smaller growth in-
crements, terminal anecdysis or inhibition of
molting by vitellogenesis and spawning (oviposi-
tion). Such inhibition is known to occur in other
crustaceans (Adiyodi and Adiyodi, 1970: Swartz,
1976).

The study of the reproductive biology of
females was based on individuals exceeding 70
mm CL (85 mm CW), which includes most of the
mature females (Haefner, 1977). This manipula-
tion insures that most of the reproductively

mature segment of the female population is treated
and reduces data bias due to variations in catch of
smaller size classes. (Figure 3).

Wigley, Theroux and Murray (1976) related col-
or of the external egg to developmental stage.
Within the red-orange, brown, dark brown, pur-
ple and black spectrum, they judged newly
deposited eggs to be light red or orange; eggs
become darker as they ripen.

A microscopic examination of eggs from 11 ex-
truded egg masses (sponges) from Norfolk Can-
yon crabs indicated a large variation in color
within the earlier stages of development (Table 3).
Because of the obvious difficulty in assigning
specific development stage by color alone, the
observed colors were grouped into early (A-C;
orange-brown) and late (D; burgundy-purple-
black) categories according to the scheme in
Meredith (1952).

A spawning cycle is suggested for red crabs in
the Norfolk Canyon area although ovigerous
females were captured in all seasons (Figure 8).

35n

30-

o 25

E
O 20

395 176 126 282

E R

□ >

A-C

JUN SEP NOV JAN

FIGURE 8. Seasonal percentage of early (A-C) and
late (D) developmental stages of extruded eggs on
ovigerous individuals and of egg remnants (ER) on
total catch of female Geryon quinquedens >70
mm CL captured in the vicinity of Norfolk Can-
yon. Blank areas indicate unidentified egg stage.
Sample size indicated by numbers above the bars.
Egg stages are described in Table 3.

P. A. HAEFNER, JR.

TABLE 3. Developmental stages of external eggs of Geryon quinquedens. Size range based on measure-
ments of 10 eggs from each sponge. Modified from Meredith (1952).

Stage

Number of

Sponges

Examined

Description

Size Range
(Mm)

Color

B
C

Egg early to late blastoderm; nearly spherical.
Minute eyes visible in larger embryos.

Pre-larval embryo. Eyes large. Abdomen and ap-
pendages well-developed, free from head. Red-
brown pigmentation present, light over entire
body, intense in eyes, cardiac and gastric regions
of carapace, and in dorsal abdominal melano-
phores.

640-740

Eye V3-V2 size of Stage D embryo; eye the only 710-780
pigmented (brown) area. Yolk abundant. Abdo-
men free. Abdomen without melanophores.

720-820

Orange

Red-orange

Red-brown
Orange

Red-orange

Burgundy
Purple (black)

The presence of females bearing egg remnants and
the low incidence of ovigerous individuals in lune
suggests a high incidence of egg hatching between
January and June. This is based on the assumption
that the presence of egg remnants indicates recent
spawning. However, at the present time it is not
known how long egg remnants remain on the
pleopods. Hatching continues through the sum-
mer and is accompanied by an increase of
ovigerous females bearing early stage (A-C) eggs.
The peak incidence of ovigerous females occurs in
November. This is characterized by a high percen-
tage of females with late stage (D) eggs and a peak
incidence of recently extruded (A-C) eggs. The
percentage of ovigerous females in the population
remains high in January, and although it is
somewhat less than that observed in November, it
is similar in the proportional makeup of early and
late stage eggs.

Information on incidence and relative abun-
dance of red crab larvae in plankton samples
would help to resolve the presence or absence of a
spawning cycle, but such data are presently
unavailable or incomplete. Winter and spring
samples off the coast of New Jersey have revealed
very few first and second zoeal stages (P.O.
Smyth, VIMS, personal communication). This in-
dicates some hatching has occurred in winter and
spring. Analyses of summer and fall samples are
incomplete.

The ovarian cycles of non-ovigerous females
(Figure 9) complements the spawning pattern.
From June to September, there was no major
change in ovarian stage. In November, an increase
in the incidence of developing (intermediate)
ovaries was accompanied by a decrease in advanc-

I00n

E
6
O

40-

20-

24 49 30 53

MAT

-J ADV.

INT.

I I IMM.

JUN SEP NOV JAN

FIGURE 9. Seasonal proportion of ovarian
developmental stages (MAT, mature; ADV, ad-
vanced; INT, intermediate; IMM, immature)
among samples of non-ovigerous female Geryon
quinquedens >70 mm CL captured in the vicinity
of Norfolk Canyon. Sample size indicated by
numbers above the bars.

SEASONAL DEEP-SEA RED CRAB

ed/mature ovaries. The lack of mature (ripe)
ovaries in November complements the peak in-
cidence of ovigerous females at that time, sug-
gesting that most of the mature females have ex-
truded their eggs. Continued progressive develop-
ment results in the higher proportion of advanced
and mature gonads observed in January.

The temperature regime appears to determine
the distribution of ovigerous females, the majority
of which were captured in 400-800 m depths where
temperatures exceeded 5° C (Figure 2.) Ovigerous
females were captured over an extensive depth
range in Norfolk Canyon although the evidence
shown for the 1201-1400 m stratum is due to only
two individuals in a small sample (Figure 10). The
highest incidence of occurence clearly fell within
the 401-800 m depth range. Females with external
eggs in early stages of development were found
deeper than 300 m and were most frequently
found within the 401-700 m depth range. The late

£ 25

201- 301- 401- 501- 601- 701- 801- 901- 1001- 1201-

300 400 500 600 700 800 900 1000 1200 1400

DEPTH (m)

□ ■
■

□ ,

FIGURE 10. Depth distribution of ovigerous red
crabs by egg development stage (A-C, D) and of
females with egg remnants (ER) on pleopods, ex-
pressed as percentage of total catch of females
>70 mm CL. Blank areas indicate unidentified
egg stage. Numbers above the bars indicate
number of females in sample. Egg stages are
described in Table 3.

TABLE 4. Density of red crabs (no. /hectare) captured by 13.7 m trawl and standing crop (in thousands of
crabs) in vicinity of Norfolk Canyon (36°30' —37°10 'N).

Depth (m)

September
1975
No. /ha Crop
lOOO's

No. /ha

anuary

1976

Crop
lOOO's

No. /ha

All

Crop
lOOO's

200-300

8.5

67.0

4.3

33.9

300-400

31.1

199.2

5.6

35.9

14.5

92.9

400-500

—

60.7

35.6

60.7

35.6

500-600

—

125.4

793.8

125.4

793.8

600-800

18.1

210.0

16.3

189.2

17.5

203.1

800-1000

23.6

337.3

51.4

734.5

30.4

434.4

1000-1200

8.6

162.5

14.4

272.1

9.2

173.8

1200-1400

31.9

703.7

—

31.9

703.7

1400-1600

1600-1800

0.1

4.9

0.1

4.9

All

13.2

2599.1

19.6

3859.3

15.8

3111.1

stage of development was most abundant at
401-800 m depth, but it was the only stage present
in the 201-300 m depth stratum. Females with egg
remnants were caught within an extensive depth
range but were markedly more prevalent in
shallower water (201-400 m) than in any other
depth.

These data do, to a certain extent, corroborate
the findings of Wigley, Theroux and Murray
(1975) of an increase of spawning females with
depth (to 640 m for their northeast sample), but
there is no evidence from the Norfolk Canyon
data to indicate seasonal differences in the in-
cidence of early and late stage eggs with depth.

P. A. HAEFNER, JR.

The presence of stage D eggs at 201-300 m (Figure
10) is due to September collections only and the
high incidence at 701-800 m is due primarily to
June collections. Only the females with egg rem-
nants are restricted to two seasons, but the data
for June and September (Figures 8, 9) are consis-
tent with that shown in Figure 10. This
preponderance of females with egg remnants in
water warmer than 8° C (in June, they were cap-
tured in 300-400 m depth stratum) may not be
coincidence. The migration of ovigerous females,
with eggs in advanced stages (D) of development,
into shallower, warmer water may enhance egg
development and hatching. Although mortality of
eggs and larval development as a function of
temperature has not been determined, it is known
that eggs survive and hatch at 15° C and larval
development proceeds at temperatures as warm as
21 °C (Perkins, 1973).

Relative density of red crabs was estimated for
the September 1975 and January 1976 surveys
(Table 4) when tow distances could be determined
with reasonable accuracy from Loran C readings.
Area fished was then computed from tow distance
and the effective fishing width of the net,
estimated to be 7.6 m (Haedrich, Rowe and
Polloni, 1975). This accounted for 55.4% of
headrope length, a value near the lower end of the
range of values computed for other types of trawls
(Griswold, Kurlyandsky and Twohig, 1971).

The relative densities were then used to com-
pute standing crop estimates for the immediate
fishing zone (Table 4). Area of each depth stratum
within the zone was determined with a planimeter
using a base chart constructed by E.P. Ruzecki
(VIMS).

The relative densities of red crabs in the area of
Norfolk Canyon were 50-95% lower than those
observed for more northeasterly areas of the con-
tinental shelf and slope (Grassle et al., 1975;
Wigley, Theroux and Murray, 1975) although a
fair degree of overlap exists within the range of
values of these three studies.

The low red crab density in the Norfolk Canyon
area is most likely a reflection of the inefficiency
of the collecting gear. The ineffectiveness of trawl
nets in capturing contagiously distributed, motile
megabenthic invertebrates has been revealed in
certain gear comparison studies (R. Cooper and J.
Uzmann, NMFS, personal communication). Ad-

mittedly, crab density calculations based on trawl
catches are tenuous because of a number of
variables (Wigley, Theroux and Murray, 1975).
However, in order to compare their data with
mine, I converted their trawl catches to relative
densities (Table 5) and found that they fell short of
the values determined by photographic sled. Their
trawl densities, ranging from 19% to 78% of the

TABLE 5. Comparison of red crab densities de-
termined by photographic sled and those com-
puted for 4.° m trawl for total geographic zone.
Data source: Wigley, Theroux and Murray (1975).
Red Crab Density Percent of

Depth (m)

Sled

Trawl

Sled Density

229-320

21.1

16.5

78.4

320-412

258.3

190.2

73.7

412-503

273.2

136.5

50.0

503-640

282.0

53.8

19.1

640-914

91.4

45.5

49.8

914-1280

61.0

37.2

61.0

1280-1646

10.9

photographically estimated densities, were com-
puted from an assumed vessel speed of 1.75 knots
for a duration of 30 minutes, and an effective
fishing width of 3 m for the 4.9 m (16 ft) trawl
(Haedrich, Rowe and Polloni, 1975).

The small trawl is apparently more effective in
capturing red crabs than is the large trawl.
Although the larger net sweeps more than twice
the area of bottom in a given unit of time, it is
unable to capture twice the number of crabs,
assuming the same density of crabs is available
(vulnerable) to the gear. Although it is difficult to
accept the apparent superiority of the 4.9 m trawl
over the 13.7 m trawl in capturing red crabs (com-
pare Tables 4 and 5), the fact is that it yielded
larger catches on an equal effort basis (0-218, x =
33; 0-197, x = 23 crabs/30 minute tow, for small
and large trawl, respectively). The relative ineffec-
tiveness of the large net may be due to a number of
factors such as lift of the net from the bottom and
rolling over crabs in depressions. Net avoidance,
however, is not likely a factor; a small net could
be more easily avoided than a larger net.

There remains the possibility that the red crab
stock in the Norfolk Canyon area may be relative-
ly sparse compared with stocks distributed north-

SEASONAL DEEP-SEA RED CRAB

easterly along the shelf and slope. This dilemma
will not be resolved until the stocks are more effec-
tively evaluated by tagging, gear comparison and
calibration.

Other studies either cannot be compared to ours
or to that of Wigley, Theroux and Murray (1975)
because of variation in gear used (Schroeder,
1955, 1959). Furthermore, they present conflicting
values. For example, Grassle et al (1975) deter-
mined red crab densities using photographic tech-
niques in DSRV Alvin. Their values from two
dives (180 crabs/ha in 4^5-490 m depth; 19.4
crabs- ha in 992-1000 m) represented 64% and
22%, respectively, of the photographic sled den-
sities reported by Wigley, Theroux and Murray
(1975) within the same geographic zone.

ACKNOWLEDGEMENTS

Gratitude is expressed to the following person-
nel at VIMS who shared their time and expertise:
E.P. Ruzecki, hydrography; E.L. Wenner, R.K.
Carpenter and J.R. Bloom, Jr., data collection;
F.J. Wojcik, data reduction; M. Williams, art
work; W.A. Van Engel and M. Roberts,
manuscript review.

LITERATURE CITED

Adiyodi, K. G. and R. G. Adiyodi. 1970. En-
docrine control of reproduction in decapod
Crustacea. Biol. Rev. 45:112-165.

Elliott, J. M. 1971. Some methods for the
statistical analysis of samples of benthic in-
vertebrates. Freshwater Biol. Assoc. Sci. Publ.
No. 25, pp. 148.

Grassle, J. F., H. L. Sanders, R. R. Hessler, G. T.
Rowe and T. McLellan. 1975. Pattern and zona-
tion; a study of the bathyal megafauna using the
research submersible Alvin. Deep-Sea Res.
22:457-481.

Griswold, B. L., Y. Kurlyandsky and P. J.
Twohig. 1971. Performance of trawls used in
joint U.S.-U.S.S.R. groundfish studies, Int.
Comm. Northwest Atl. Fish. Res. Doc. 71/117,
pp. 26.

Haedrich, R. L., G. T. Rowe and P. T. Polloni.
1975. Zonation and faunal composition of
epibenthic populations on the continental slope
south of New England. J. Mar. Res.
33(2):191-212.

Haefner, P. A., Jr. 1977 Reproductive biology of
the female deep-sea red crab, Geryon quin-
quedens, from the Chesapeake Bight. Fish. Bull.
75(1):91-102.

Haefner, P. A., Jr. and J. A. Musick. 1974. Obser-
vations on distribution and abundance of red
crabs in Norfolk Canyon and adjacent con-
tinental slope. Mar. Fish. Rev. 35(l):31-34.

Holmsen, A. A. and H. McAllister. 1974.
Technological and economic aspects of red crab
harvesting and processing. Univ. Rhode Island
Mar. Tech. Rep. No 28. pp.35.

Intes, A. and P. LeLoeuff. 1976. Etude du crabe
rouge profond Geryon quinquedens en Cote
d'lvoire. I. Prospection de long du talus con-
tinental; resultats des peches. Doc. Scient. Cen-
tre Rech. Oceanogr. Abidjan. VII(1):101-112.

LeLoueff, P., A. Intes and J. C. LeGuen. 1974.
Note sur les premiers essais de capture du crabe
profond Geryon quinquedens en Cote d'lvoire.
Doc. Scient. Centre Rech. Oceanogr. Abidjan.
V(l-2):73-84.

McRae, E. E., Jr. 1961. Red crab explorations off
the northeastern coast of the United States.
Com. Fish. Rev. 23(5);5-10.

Meade, T. L. and G. W. Gray, Jr. 1973. The red
crab. Univ. Rhode Island Mar. Tech. Rep. Ser.
No. 11, pp.21.

Meredith, S. S. 1952. A study of Crangon crangon
L. in the Liverpool Bay area. Proc. Trans. Liver-
pool Biol. Soc. 58:75-109.

Perkins, H. C. 1973. The larval stages of the deep
sea red crab, Geryon quinquedens Smith,
reared under laboratory conditions (Decapoda:-
Brachyrhyncha). Fish. Bull. 71(l):69-82.

Schroeder, W. C. 1955. Report on the results of
exploratory otter trawling along the continental
shelf and slope between Nova Scotia and
Virginia during the summers of 1952 and 1953.
Papers Mar. Biol. Oceanogr. Deep-Sea Res.,
Suppl. Vol. 3:358-372.

Schroeder, W. C. 1959. The lobster, Homarus
americanus, and the red crab, Geryon quin-
quedens, in the offshore waters of the western
North Atlantic. Deep-Sea Res. 5:266-282.

Swartz, R. C. 1976. Sex ratio as a function of size
in the xanthid crab, Neopanope sayi. Amer.
Nat. 110:898-900.

62 P. A. HAEFNER, JR.

Varga, S., A. B. Dewar and W. E. Anderson. Wigley, R. L.. R. B. Theroux and H. E. Murray.

1969. Survival of red crabs held on ice and ■ 1975. Deep-sea red crab, Geryon quinquedens,

refrigerated air. Halifax Dept. Fish. For. Tech. survey off northeastern United States. Mar.

Rep. No. 2, pp.3 Fish. Rev. 37(8):1-21.
Wenner, A.M. 1972. Sex ratio as a function of size

in marine Crustacea. Amer. Nat. 106:321-350.

Proceedings of the National Shellfisheries Association
Volume 68-1978

FISHERY BIOLOGY OF SPINY LOBSTER

(PANULIRUS ARGUS) of the GUAJIRA PENINSULA OF
COLOMBIA, SOUTH AMERICA, 1969-1970

H. J. Squires1 and G. Riveros2

UNDP/FAO PROYECTO PARA EL DESARROLLO
DE LA PESCA MARITIMA EN COLOMBIA, BOGOTA, D.E.

ABSTRACT

The fishery for Panulirus argus of the Guarjira Peninsula of Colombia is reported to
average 550 tons (total weight) a year since 1969. However, an annual catch of 20 tons
from traps in an estimated area of 40 km2 in 1971 is evidence of a potential yield of
1,000 tons annually from the total area of about 2,000 km1 of smooth bottom where
turtle grass and coralline outcroppings occur in depths of 5-50 m. Spawning (and
possibly molting) in almost all mature females was estimated to occur every two mon-
ths. With molt increments of about 6mm cl. hypothetical gains from original weight on
molting are approximately 35% for one, 70% for two. 100% for three and 150%for
four molts on the average. The period of oogenesis (development of ova in ovaries) is
about equal to embryogenesis (development of embryos in eggs on pleopods) and most
females are ready to spawn again when eggs are hatched. About 300,000 eggs are car-
ried at 75 mm cl and 1 million at 110 mm cl. Females carry eggs as early as 64 mm cl but
about 50 % were immature at 71 mm cl. A minimum size of 76 mm cl (at least) is
recommended for this area where smaller ones are sometimes exploited.

INTRODUCTION

Spiny lobsters (Panulirus argus and P.
laevicauda) are found all along the coast of the
Guajira Peninsula, the eastern part of the Colom-
bian coast adjacent to Venezuela (Figure 1). A
commercial fishery for lobsters occurs west of
Cabo de la Vela where there is a shelf gradually
sloping to the 50 m contour and averaging 20 km
in width. Where lobsters are found is estimated to
be 130 km long and 15 km wide, an area approx-
imately 2,000 km2. All this area is not necessarily
fished by the Guajiros, a tribe of Arawak Amerin-
dians who dive reportedly to about 10 m deep (us-

Present addresses:

'122 University Avenue, St. John's. Newfoundland
Canada

2Departamento de Planacion, Ministerio de Agricultura,
Bogota D. E.

ing face masks only), nor by other coastal fisher-
men who use Florida-type wooden traps in depths
of 10-25 m. The landings reported since 1969
(Table 1) average about 550 tons (live weight) a
year, a small but significant amount when com-
pared with the total annual Caribbean catch of
13,000 tons (Gulland, 1970). The fishery provides
an important cash income for the coastal peoples
of the Guajira.

The coastlands of the Guajira Peninsula are
low-lying and semi-desert with several large
lagoons, some of which are used for solar salt pro-
duction and have rocky or sandy substrate, while
others are fringed at least partly by mangroves
and have mud substrate. Just offshore throughout
the area are extensive beds of turtle grass
(Thalassia testudinum) interspersed with smooth
sandy bottom and outcroppings of coralline rock

H.J. SQUIRES AND G. RIVEROS

3°W

R IOH ACH A
■'Camarones

11«

COLOMBIA

PENINSULA DE
LA GUAJIRA

VENEZUELA

Spmy lobster
t i shi ng area

'/W^fl© 6 8°

FIGURE 1. Map of the Guajira Peninsula of Colombia showing fishing grounds for spiny lobsters,
Panulirus argus and P. laevicauda, and place names used in the text.

or fossil oyster reef. Immediately west of Cabo de
la Vela is an indentation of the coast (Figure 1)
where large numbers of small lobsters are reported
throughout the year, and it is possible that current
patterns encourage settlement of lobster larvae
from the plankton. Navigation charts show cur-
rents of up to 1.2 knots setting westward off Cabo
de la Vela. These would be under the influence of
northeast and easterly trade winds in the area.
Also near the coast are weak counter currents (0.9
knots) setting eastward along the shore of the
Guajira Peninsula. It is likely, therefore, that a
weak anti-cyclonal gyre is set up just west of Cabo
de la Vela.

The present study of the spiny lobsters in this
area was undertaken to make an estimate of their

potential yield to a fishery and to determine some
essential features of their biology such as repro-
duction, growth and feeding habits. -

TABLE 1. Annual catches of Panulirus argus from
the Guajira Peninsula of Colombia, 1969-74.

Year

Total weight
tons

1969
1970
1971
1972
1973
1974

800
870
540
300
270
420

BIOLOGY OF SPINY LOBSTER

mJJ

$ 5

FIGURE 2. Histogram of monthly catches of
Panulirus argus handled by a processing com-
pany, including those caught by Florida-type
wooden traps and diving near Riohacha, Guajira
Peninsula of Colombia, 1971-72,

METHODS

Monthly trips were made to Riohacha (Figure 1)
where freezing and cold storage facilities were
located and the spiny lobster catch being process-
ed for export (total cold storage was about 20 tons
and freezing capacity about 3 tons daily in 1970).
Data on catch were supplied by the processing
company and INDERENA (Instituto de Desarrollo
de los Recursos Naturales Renovables).

Measurements and examinations of the spiny
lobsters were made from random samples of live
catches brought to the company for processing.
Samples were taken by setting aside all specimens
from a segment of a heap of lobsters emptied from
burlap bags on the concrete floor of the processing
room. Each lobster in the samples was measured
and examined as follows:
Lengths and weights to the nearest mm or g.

Each lobster was weighed whole (TW) on a
commercial balance (accurate to about 5 g);

carapace length (CL) from the anterior edge of the
carapace between the two large supraorbital
spines to the posterior edge in the mid-dorsal line
with vernier calipers; total length (TL) on a
measuring board (stretched with back against the
board) with the supraorbital spines against the
headboard (3 cm high) and the length read where
the tip of the telson reached on the board; the ab-
domen (tail) was then separated from the thorax
(head) and weighed on the balance (AW), then
stretched on the measuring board back down with
the anterior edge of the first segment pressed
against the headboard and the length (AL) read
where the tip of the telson reached on the board;
the greatest width of the abdomen (at the second
segment) was taken on the measuring board by
pressing the ventral edge of the pleuron of one side
against the headboard and reading the width
where the edge of the pleuron of the other side
reached on the board.
Examination for maturity, etc.

Ovaries were removed from the thorax and
their colour recorded. Greater diameter of a few
ova from part of the ovary was measured under
magnification (10X) on a transparent mm grid.
When eggs were carried on the pleopods they were
removed before weighing the abdomen. The color
of the egg mass was recorded and the phase of em-
bryo development noted under magnification
(10X). Hardness or newness of the shell, presence
of epifaunal growths, etc., were also recorded
(New shell was defined as recently molted but suf-
ficiently rigid to permit capture and handling. It
was bright in color and free from epifauna or
discoloration and buckled under light pressure).
Stomachs seen to contain food were taken out and
preserved in formalin for later examination.

Temperatures and salinities were taken with a
portable salinometer from a beach site, from the
head of the jetty at Riohacha and from lobster
fishing stations by the R/V CHOCO (March 9-16,
1970.

Landings from lobster traps and from diving for
one year were provided by one of the lobster pro-
cessing companies at Riohacha.

BIOLOGY

Length-weight relationships.

Regression equations for total length at each
carapace length in males and females were as
follows:

H.J. SQUIRES AND G. RIVEROS

Male TL = 2.34 CL + 39.4 (N = 500);
Female TL = 2.40 CL + 47.9 (N = 493).

The rate of increase in total length relative to
carapace length appeared to be greater in females
than in males over the range of commercial sizes
(Figure 3). However, in spite of the large numbers
used an appreciable overlap in the regression coef-
ficients is apparent in a "t" test (Spiegel, 1960)
showing a range of 2.24 - 2.44 in males and 2.29 -
2.51 in females so that both could be similar
(Table 2).

TL ■ 2-40CL* 39-4
N >493

%■

66 86 106 126

CARAPA I IENGIH-""

FIGURE 3. Regression of Total Length (TL) on
Carapace Length (CL) in male and female
Panulirus argus from the Guajira Peninsula of
Colombia.

Regression equations for abdomen length
relative to carapace length give divergent slopes as
follows (Figure 4):

Male AL = 1.34 CL + 32.1 (N = 500);

Female AL = 1.56 CL + 17.1 (N = 493).
The slope for females is the steeper indicating that
the increase in length of abdomen relative to
carapace length is greater in females than in males.
The ranges in coefficients shown by a "t" test sup-
port this, being 1.27 - 1.41 in males and 1.51- 1.61
in females (Table 2).

■ I. sec L + 17'1

1-34CL432 I
N> 600

66 «6 106

Carapace length min

FIGURE 4. Regression of Abdomen Length (AL)
on Carapace Length (CL) in male and female
Panulirus argus from the Guajira Peninsula of
Colombia.

TABLE 2. Regression equations and "t" test of re-
gression coefficients of length and weight relation-
ships of Panulirus argus from the Guajira Penin-
sula of Colombia. Calculation of "t" test from
Spiegel (1961):

Coefficient a, ±

^/N^I

N = 500 (M) or 493 (F); and s, , =

where t = 1.65;
S,2 — fl|Sxy

Sx =

Regression equations

Male TL = 2.34 CL + 39.4

Female TL = 2.40 CL + 47.9

Male AL = 1.34 CL +32.1

Female AL = 1.56 CL + 17.1

Male TW =3.29 AW -3.5

Female TW = 3.15 AW -20.9

Range of regression
coefficients at 95%
confidence limits
2.24—2.44
2.29 — 2.51

1.27 — 1.41
1.51 — 1.61

3.28 — 3.30
3.13 — 3.17

Regression equations for total weight (TW) at
each abdomen (tail) weight (AW) are useful for
converting the "tail" weight of commerce to total

BIOLOGY OF SPINY LOBSTER

weights for estimates of yields from lobster
populations. They are as follows:

Male TW = 3.29 AW -3.5 (N =500);

Female TW = 3.15 AW — 20.9 (N = 493).

(Figure 5)

In these equations the coefficients have ranges of
3.28 - 3.30 and 3.13 - 3.17 in males and females,
respectively (Table 2) so may be considered to be
different at the 95% confidence limit. For practical
purposes the conversion of tail weight to total
weight may be done by a factor of 3.2 if it is
known that the numbers of males and females in
the catches are equal (Squires, 1974). On the
average the tail weight is about 31% and 33% of
the total weight in males and females, respective-
ly, or 32% with males and females combined
(Table 3).

150 250 350 450 550

»BD0 HEN WEIGHT 19!

FIGURE 5
Abdomen
Panulirus
Colombia.

. Regression of Total Weight (TW) on
(Tail) Weight (AW) in male and female
argus from the Guajira Peninsula of

2500
2000

1500-

lOOO
800

f 600.

r 500

" 400
*

4 300

Loq T W.-5-655.2-79 2 LogCL
N:4»J
I »0 94

109 TWs. 2- 287* 2-5 78 Log CL
NmSOO
'-0-90

40 SO 70 100 150 200

CARAPACE IENGTH-MM

FIGURE 6. Regression of Total Weight (TW) on
Carapace Length (CD in male and female
Panulirus argus from the Guajira Peninsula of
Colombia.

Equations for obtaining total or abdomen
weights from carapace lengths (Riveros, 1972)
have less practical use. They are as follows:

Male Log AW = 2.5146 Log CL — 2.6782

(N = 500);
Female Log AW = 2.4331 Log CL — 2.4302

(N=493). (Figure 7).

Male Log TW = 2 . 5780 Log CL — 2 . 2873

(N = 500);
Female Log TW = 2.7921 Log CL — 2.6555

(N=493) (Figure 6).

Maturity

Size at first maturity. In females the minimum
size of mature lobsters (bearing eggs on the
pleopods) was 64 mm CL in these samples.
However, the minimum size found with large ova
ready to be laid was 55 mm CI, but if this lobster
molted before spawning (which is likely) it would
be about 61 mm CL when carrying eggs. Only 5%
of the females were immature at 71 mm CL and no
juveniles or immatures were more than 94 mm CI

H.J. SQUIRES AND G. RIVEROS

TABLE 3. Average abdomen and total weiglits at average carapace and abdomen lengths in 450 male and 450 female
Panulirus argus from the Gnajira Peninsula of Colombia.

Carapace

Abdomen

lengths

Abdomen weights

Total

weights

Percent-

AW of TW

length

Male

Female

Male

Female

Male

Female

Male

Female

100

131

146

107

104

168

190

114

112

210

237

120

256

291

127

128

119

309

354

134

136

113

140

368

420

140

143

132

170

431

515

147

151

153

180

500

574

154

159

177

217

579

663

161

167

203

247

664

757

101

167

175

230

279

757

858

10b

174

182

260

314

852

968

111

181

190

292

352

957

1088

116

187

108

326

392

1069

1214

121

194

206

362

434

1187

1346

126

201

214

400

479

1319

1530

* 100

° 80-1

Log AW » -24302*2-4331 Log CL
N*493

Log A W = -2.6782*2-5146 Log C
M.SOO

30 40 60 801OO

C AH APACF LENGTH MM

FIGURE 7. Regression of Abdomen (Tail) Weight
(TW) on Carapace Length (CL) in male and female
Panulirus argus from the Guajira Peninsula of
Colombia.

(Riveros, 1972). Abdomen widths were greater in
proportion to carapace length by about 6% after
maturity (Table 4).

In males the smallest matures were 66 mm CL
and very few juveniles (5%) were larger than 85
mm CI (Riveros, 1972). The 66 mm CI cor-
responds to an average tail weight of 79 g or 2.9 oz
in males and 99 g. or 3.6 oz in females. Minimum
accepted commercial size is a 4 oz (114 g) tail

TABLE 4. Average width of abdomen in female Panu-
lirus argus when immature and when mature; expressed
as a percentage of CL and TL (total length).

Carapace

Total

Abdomen width

length

as percent
CL

of
TL

Maturity

194

Mature

Immature

200

Ovigerous

Immature

207

Mature

BIOLOGY OF SPINY LOBSTER

which would be from a male of 76 mm CL and a
female of 71 mm CL. (A minimum size of 76 mm
CI was recommended to Government for inclusion
in legislation to protect the lobster resource).

Male maturities. After males became mature
(with large vasa deferentia purplish in color) they
continued to retain full maturity irrespective of
season (Riveros, 1972). Maturities could be
categorized into three phases (Table 5) with con-
siderable overlap in sizes of specimens.

Female maturities. Four phases of maturity of
ova in ovaries (oogenesis) were defined as follows:
I, immature or juvenile; II, maturing; III, mature
and IV, spent and recovering (Table 6). In all
phases there were oocytes or small ova present in
the ovarian stromae, but these were beginning to
be predominantly orange in color and slightly
larger in Phase IV.

Macroscopic phases of embryo development
(embryogenesis) in eggs on pleopods could be seen

TABLE 5. Phases of maturity in 500 male Panulirus argus from the Guajira Peninsula of Colombia, 1969-
70.

Phase Category Testes Vasa deferentia Diameter Spermatophore Range 50% of

condition size and ofv.d. glands of of phase

and color color 5th legs CL at CL

mm mm mm

>1 Small 40-85 65

1-2 Medium 62-110 83

3-4 Large 66-158 100

Immature

Small.

Small,

translucent

Maturing

Medium,

Medium.

opaque

yellowish

purplish

III

Mature

Large,

opaque

purplish

whitish

TABLE 6. Phases of maturity of ova in ovaries (oogenesis) of Panulirus argus from the Guajira Peninsula
of Colombia, 1969-70.

Phase

Category

Color of eggs

Greater

Phase of

diameter

ovary

of egg

development

Bright red

0.5

Orange

0.6

Brownish

0.7-0.8

III

I Full yolk, no eye spot

II Eye spot a flat black crescent

III Eye spot round, limb structure visible;
prenaupliosoma

under low magnification (10X). Three phases were
defined: the first in which no eye spot was present,
the second with the eye spot merely a slit or black
crescent and the third when the eye spot was
rounded and limbs of the prenaupliosoma could
be distinguished (Table 7). These phases cor-
responded with Phases IV, II and III, respectively,
of ovarian development indicating that by the
time embryos were ready to hatch the ova were
almost ready to be extruded. In a very few large
females carrying eggs the ovaries showed only an
early phase of development. Incidentally, the ear-
ly phases of embryo development in eggs on
pleopods were seen more frequently than the later
phase (Table 8).

Abdomen width as an indication of maturity.
Immature females had narrower abdomens than
mature females of the same CL. As a percentage of
CL average abdomen widths were about 67% in

TABLE 8. Incidence of macroscopic phases of em-
bryo development (Table 6) in samples of Panul-
irus argus (August, 1969 to May, 1970) from the
Guajira Peninsula of Colombia.

Month

Phase I

Phase II

Phase III

Number

(red)

(orange)

(brown)

examined

Aug

Sept

Oct

Nov

Dec

Jan

Feb

100

Mar

Apr

May

0
100

27
14
14

immature and 72% in mature females. In the 234
females included in this comparison the change
from immature to mature abdomen widths oc-
curred at about 70 mm CL (Table 4).

Fecundity. Counts of eggs from 19 females from
these samples by Herazo (1971) gave average
numbers of just over 300,000 at a size of 75 mm
CL and more than one million at 110 mm CI
(Figure 8).

12-

10-

z a-\

in
o
o

3
Z

70 90

CARAPACE

I 10
LENGTH

— i

130

FIGURE 8. Number of eggs at each Carapace
Length (CL) in Panulirus argus from the Guajira
Peninsula of Colombia (Counts of eggs from
pleopods of 19 females).

BIOLOGY OF SPINY LOBSTER

Stomach contents

Of the 93 stomachs examined (only those with
food are included) 40 percent contained fish re-
mains (bone and tissue fragments). Crustacean re-
mains (fragments of crabs and shrimps) were in
30% of the stomachs, and molluscan shells
(bivalves and gastropods) in 20%. The rest com-
prised low incidence of fragments of echinoderms
and plants. Sand was present in small quantities in
all. Molluscan shells and echinoderm remains
were frequently seen in intestines but only
stomachs were examined in detail.

Shell condition

The highest percentages with new shells were in
May (18%), July (6%) and September (10%). In
other months the percentages varied from 1-6%
(Table 9).

Temperature and salinity

Average water temperatures on the fishing
grounds were 27 C from 1-10 m deep and 24 C
from 10-20 m during periods of observation
(Squires et al., 1974). Salinities observed were

34-37%0.

TABLE 9. New shells in monthly samples of
Panulirus argus from the Guajira Peninsula of
Colombia, 1969-70.

Month

May

lune

July

Aug

Sept

Oct

Nov

Dec

Jan

Feb

Mar

Apr

May

Percent with

Number

new shell

examined

164

143

195

ESTIMATE OF YIELD AND DENSITY OF SPINY
LOBSTERS ON THE FISHING GROUNDS

A comparison of landings from trap fishing and
from diving indicates that in 1971 and 1972 the
divers contributed more than 85% to the landings
(Figure 2). In the month to month fluctuations in
landings September-November and March-June
produced 8,000-16,000 kg a month while July and
August had less than 3,000 kg and December the
least with only 1,500 kg (Riveros, 1972). These
fluctuations were reportedly the results of changes
in fishing effort because of weather conditions or
tribal activity of the Guajiros.

Fishing with traps, operated over an area of ap-
proximately 40 km-' near Riohacha (about 20 km
by 2 km), caught about 20,000 kg in 1971. About
200 traps were hauled daily with not less than
three days between hauls for any one trap. The
maximum traps in use was 1,000. Catch per area
was:

20,000 kg
40 km2

or 500 kg per km*

Assuming that lobsters could have been obtained
from a total area of potential fishing grounds be-
tween depths of 5 and 45 m (conservatively 2.000
km- in area) between Cabo de la Vela and
Camarones (Figure 1), the annual yield would be
about 1000 tons. The total catch in 1971 was
reported as 540 tons (tail weight =170 tons).

From a potential yield of 1,000 tons and an
average weight of about 400 g for each spiny
lobster at commercial sizes, the density of lobsters
on the grounds would be about 1 to every 400 m2.
This estimate is obtained from the total number of
commercial lobsters in 1,000 tons (about 2,-
500.000) plus an equal number of pre-commercial
sizes, and assuming that they were all evenly
distributed over the shelf area.

DISCUSSION

The fishery

Average

5 Total

927

Although the average catch of fishermen using
traps off Riohacha was approximately 2 tons each
it did not exceed the average catch of the Amerin-
dians diving for lobsters. The latter do not have a
strong incentive to catch more. Their need for
cash income is more than satisfied by the rate of
fishing, and they fish only when there is no fiesta

H.J. SQUIRES AND G. RIVEROS

or other tribal activity. Although their "free" div-
ing (with face mask only and with no fins) is
relatively effective compared with trapping, they
cannot dive during windy weather when the sand
is stirred up and visibility is low in the water and
sharks are more dangerous. Trapping would
reduce the hazards. The investment in larger boats
and traps, however, would require a much larger
catch to provide the same level of income to these
fishermen.

Fishery regulations prescribe a minimum size, a
"veda" or closed season and non-retention of egg-
bearing females. Because several market outlets
are available, the Guajiros sell only to buyers who
will take all sizes of lobsters. The closed season is
not observed. There is, however, a natural season
all but closed to the divers during about three
months of heavy winds, and since there are
uniformly warm water conditions throughout the
year, there is no season such as a breeding season
when closure would be useful. Also, since most
adult females are either carrying eggs or ready to
lay eggs, saving the egg-bearing ones would not be
different from saving the non-eggbearing. The on-
ly regulation, therefore, that would be useful is the
one related to minimum size which would add ap-
preciably to the total weight of lobsters harvested
each year if kept strictly (Table 10). A minimum
size suggested is 76 mm CL which could be in-
creased in subsequent years if accepted by the
fishermen.

Weight gains per molt.

Hypothetical weight gain per molt may be
estimated from average weights at given carapace

lengths when the increment in length with each
molt is known (Squires, 1970; Squires et al, 1971;
Riveros, 1972). The average molting increment of
8 mm CL estimated by Riveros (1972) may be ex-
cessive in view of the estimates given by others for
this species. Munro (1973) reviewing several
works from different areas suggests 30 mm per
year in four molts; Peacock (1974) for Antigua
and Barbuda, 21-35 mm in 4-5 molts and Beau-
mariage and Little (1975) 15 mm, presumably in
two molts in Florida. Olsen et al (1972)
documented slower growth in females than in
males: 4-7 mm per molt compared with 4-8 mm.
In this paper, 6 mm increments in CL per molt in
males and females is taken for calculations of
weight gains (Table 10).

Starting at 59 mm CI (178 g) weight gains of
males would be 35% in one, 63% in two, 105% in
three and 142% in four molts. Corresponding
gains in females would be 39%, 74%, 111% and
159% of the original weight of 190 g at 59 mm CI.
Percentage gains in abdomen weight were slightly
less (Table 10). Olsen et al (1972), however,
postulates that molting in females is less frequent
than in males so that increases in weight would
take place over a longer time.

Demonstrating weight gain in lobsters (if left to
molt) is a way to convince fishermen how much
weight is lost to a fishery if lobsters smaller than
regulation size are taken. Also it shows them that
small lobsters will soon gain weight if left on the
grounds where they may be caught again later
after release.

TABLE 10. Hypothetical gains in weight of male and female Panulirus argus using average CL increments
of 6 mm in each molt and an original CL of 59 mm (Calculated from regression equations of total weight
(TW) and abdomen weight (AW) on carapace length (CD). (Figures 6 and 7).

Average

Percent gain on original

weight

total

weights

abdomen weights

Total

weights

Abdomen weights

Male

Female

Male

Female

Male

Female

Male

Female

178

190

240

265

107

290

330

100

126

365

400

121

147

105

111

430

490

138

174

142

150

104

515

600

le>2

20o

189

216

131

142

BIOLOGY OF SPINY LOBSTER

Reproductive potential.

Chittleborough (1974) found that individual
mature females of P. longipes cyngus spawned ap-
proximately every second month when kept in
aquaria under high temperature conditions similar
to those prevailing in tropical areas. Berry (1971)
also noted repeated spawnings of P. homarus ap-
proximating once every two months while the
warm temperatures of summer prevailed in South
Africa. Squires (1973) suggested that reproductive
cycles under tropical conditions were short, and
that spawning in mature female lobsters of the
Guajira occurred every 2.5 months throughout the
year. Olsen et al. (1972), from direct observations
of female P. argits in the Virgin Islands during
underwater studies, remarked that "females may
reproduce several times a year".

During the present investigations the comple-
tion of development of embryos in eggs (em-
bryogenesis appeared to be approximately equal
to the development of ova in ovaries (oogenesis).
Also, the monthly percentage of mature females
carrying eggs was frequently in excess of 50%
(seven times out of eleven), and the average
percentage was 50% in the eleven samples examin-
ed (Table 11). Although data were obtained from
fairly small numbers and samples were not obtain-
ed in some months, every second month of
1970-71 had the greater percentage carrying eggs
(Table 11). Since the samples were taken almost
exactly one month apart and from approximately
the same area, the effects of synchrony in bi-
monthly spawning might be indicated from these
data. Apparently most mature females spawned
every second month.

New shells.

Although an average of only 5% of shells ex-
amined appeared to be new, some were present in
most months (Table 9). The low percentages may
have been caused by the following: the inability of
the examiner to recognize new shells, the selection
by divers against soft shells, discarding of injured
soft-shelled lobsters before bringing to the factory
and possibly by recently molted lobsters being
more secretive in behaviour. As indicated by Chit-
tleborough (1974), it is likely that molting follow-
ed hatching of larvae from the eggs, and preceded
egg- bearing. Where spawning was frequent,

TABLE 11. Percent of mature female Panulirus
argus ovigerous in monthly samples from the
Guajira Peninsula, Colombia, 1969-70.

Months

Percent

Number of Mature

ovigerous

femali

;s examined

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

Jan

Feb

Mar

Apr

May

Average

50 Total

347

therefore, lobsters with new shells would be pre-
sent in all months. In the first six months of this
study (May-October, 1969) each alternate month
had a higher percentage of new shells (Table 9).
This appeared to correspond with the months
following those in which peaks of spawning oc-
curred (Table 11).

ACKNOWLEDGEMENTS

We wish to thank Mr. Gabriel Durana,
Manager of "Crustaceos de la Guajira" at
Riohacha and Mrs. Durana for their hospitality
and assistance; also Mr. Bernard Herazo for data
on egg counts.

LITERATURE CITED

Beaumariage, D.S. and E.J. Little. 1975. Status
report of Florida's research on spiny lobster.
Proc. Gulf & Car. Fish. Inst. 28:102-107.

Ben-Tuvia, A. y C. E. Rios. 1970. Informe de un
crucero del CHOCO a la isla de Providencia y
los bancos adyacentes de Quitasueno y Serrana

H.J. SQUIRES AND G. RIVEROS

en los territories insulares de Colombia. Pro-
depesca en Colombia Communicaciones 2, 45

P-

Berry, P.F. 1971. The biology of the spiny lobster
Pamilirus homarus off the east coast of South
Africa. Invest. Rep. Oceanogr. Res. Inst.
28:1-75.

Chittleborough, R. G. 1974. Western rock lobster
reared to maturity. Aust. J. Mar. Freshwat. Res.
25:221-225.

Gulland, J. A. 1970. The fish resources of the
ocean. FAO Fish. Tech. Pap. 97, 425 p.

Herazo, B. 1971. Reproduccion de Pamilirus argus
en la costa de la Guajira colombiana. Tesis de
Licenciado en ciencias. Fundacion Universidad
deBogota(JTL),61p.

Munro, J.L. 1974. The biology, ecology and
bionomics of Caribbean reef fisheries. VI.
Crustaceans (spiny lobsters and crabs). Res.
Rept. Zool. U. W. 1.3, 57p.

Olsen, D.A., W. Herrnkind and I. G. Koblick.
Ms. 1972. Ecological study for the development
of lobster management techniques. PRINUL
(Puerto Rico International Undersea Labora-
tory) Special Report No. 1, 71 p.

Peacock, N. 1974. A study of the spiny lobster

fishery of Antigua and Barbuda. Proc. Gulf and
Carib. Fish. Inst. 26:117-130.

Riveros, G. 1972. Spiny lobsters Pamilirus argus
and P. laevicauda on the Caribbean coast of
Colombia with particular reference to their
biology and the fishery for both species on the
coast of the Guajira Peninsula. M.Sc. thesis,
Memorial University of Newfoundland, 115 p.

Spiegel, M.R. 1961. Theory and problems of
Statistics. Schaum's Outline Series in
Mathematics. McGraw-Hill. 359 p.

Squires, H. J. 1970. Lobster (Homarus
americanus) fishery and ecology in Port au Port
Bay, Newfoundland, 1961-65. Proc. Nat.
Shellfish. Assoc. 60: 22-39.

Squires, H. J. 1973. El potencial reproductive de
los crustaceos decapodos. Bol. Museo del Mar
(Univ. Bogota) 5: 3-7.

Squires, H. J. Ms. 1974. Length and weight rela-
tionships in shrimps. Govt. Consultation on
Shrimp Resources in CICAR area. FAO/FIR:
SR/74/W.P. 5, 7p.

Squires, H. J., G. E. Tucker and G. P. Ennis. 1971.
Lobsters (Homarus americanus) in Bay of
Islands, Newfoundland, 1963-65. Fish. Res. Bd.
Can. Manuscr. Rept. Ser. (Biol.) 1151, 58 p.

PROCEEDINGS OF THE NATIONAL SHELLFISHERIES ASSOCIATION

ABSTRACTS OF THE TECHNICAL PAPERS PRESENTED

AT THE 1977 NSA CONVENTION

MEXICAN MOLLUSCAN FISHERIES

OF THE GULF OF MEXICO
AND THE CARIBBEAN : 1970-1975

Erik Baqueiro and Craig B. Kensler

Centro de Ciencias

del Mar y Limnologia

Universidad National Autonoma de Mexico

Mexico 20, D.F., Mexico

Molluscan fishery statistics for the Mexican
Gulf and Caribbean have been analyzed for
1970-1975 for each molluscan group or by-pro-
duct landed, and for each of the six coastal states.
The statistics listed the landings by the following
"classes" of molluscan groups or by-products: sea
clam, river clam, squid, mixed shells (industrial),
conch meats, mixed molluscan meats, oyster with
shell, oyster meats and octopus. During 1970-1975
total molluscan landings of 189,131 metric tonnes,
valued at $29,637,244 (USA), were reported for
the area — averaging about 31,522 tonnes, worth
about $4,939,541 (USA), per year. The most im-
portant molluscan fishery of the region during the
period was for "oyster with shell" (mainly
Crassostrea virginica), followed far behind by the
octopus fishery (Octopus vulgaris and O. maya.)
The oyster with shell fishery represented about
84% by weight and 50% by value of total
molluscan landings, including by-products, from
the Mexican Gulf and Caribbean region during
1970-1975. The octopus fishery represented 8.3%
by weight and 25.1% by value of total molluscan
landings. Veracruz was by far the most important
state for molluscan landings. During the period,
51.8% of the total weight of landings, and 31.9%
of total value, from the region were reported from
the state of Veracruz. The state of Tabasco was se-

cond in total weight landed (29.5%) and the state
of Campeche was second in total value of landings
(23.1%) for the entire region.

A DISEASE SURVEY OF

NEW ENGLAND SOFT-SHELL

CLAMS, MY A ARENARIA

Robert S. Brown

Marine Pathology Laboratory

Department of Animal Pathology

University of Rhode Island

Kingston, Rhode Island 02881

A field survey for possible pollution-related
diseases of the soft-shell clam was initiated in
January, 1976. To date, more than 1500 clams
from 10 sites of differing types and degrees of
pollution have been histopathologically examin-
ed. Lesions noted included: disturbances of
growth (neoplasia, hyperplasia, hypoplasia), reac-
tion to injury (hemocytosis, inflammation), pre-
sence of parasites (bedsonia, protozoan, meta-
zoan, and accumulations of orange-brown
pigmented bodies (both intra- and extracellularly).

The prevalence of these lesions varied between
sites suggesting environmental influences.
Cytologic examination, coupled with a signifi-
cantly increased mortality during a 10 month
study indicated the malignancy of the neoplastic
disease.

HISTOCHEMICAL ANALYSES OF PIGMENT

ACCUMULATIONS IN

MERCENARIA MERCENARIA L. AND

MY A ARENARIA L.

ABSTRACTS

Robert S. Brown and Carole J. OToole

Marine Pathology Laboratory

Department of Animal Pathology

University of Rhode Island

Kingston, Rhode Island 02881

Histopathologic analysis of Mercenaria col-
lected from Massachusetts, Rhode Island and New
Jersey demonstrated accumulations of pigments of
three types: 1) irregular, 2-20 (im diameter,
orange-brown staining (H&E) bodies, present ex-
tracellularly in the alimentary tract epithelium and
gonadal connective tissue, and intracellularly in
renal epithelium; 2) spherical 7-12 ^m diameter
eosinophilic concretions, present intracellularly in
renal epithelium; and 3) 30-200 pm diameter
melanotic casts present in renal tubular lumens.

Only type 1 pigment was found in Mya col-
lected throughout New England, and was present
in lesser amounts than in Mercenaria from adja-
cent locations. This pigment had morphological
characteristics of lipofuscins (brown staining
bodies of oxidized lipids) found in vertebrates. All
three pigment types had histochemical charac-
teristics of lipofuscins.

Based on the examination of over 200
Mercenaria and 1500 Mya, the accumulation of
these pigments appears to be a normal
physiological process, although abnormally large
accumulations were noted in clams from certain
environments.

CULTURE OF HATCHERY-SPAWNED

MERCENARIA MERCENARIA IN

MASSACHUSETTS

H. Arnold Carr

Massachusetts Division

of Marine Fisheries
Sandwich, Mass. 02563

Coastal towns, which have the prime respon-
sibility for managing shellfish in Massachusetts,
are finding hatcheries to be one of the best sources
for hard clams (M. mercenaria). During 1976, 12
towns bought hatchery stock between 5-14 mm
(longest diameter). A variety of on-bottom and
off -bottom systems was used to isolate the clams
from predators. Growth varied with system de-

sign, density of clams, and substrate type. Sur-
vival prior to winter, though 90% or more, must
be qualified. During the winter, survival was
80-90% in rafts and widely variable in pens lying
in intertidal and shallow subtidal areas. The suc-
cess of most transplants into natural, unprotected
bottom appears related to the number of green
crabs observed in the transplant site. Although the
theoretical yield of this technique is high, the ac-
tual benefit to a town management program re-
mains to be proven.

ULTRASTRUCTURAL EVIDENCE THAT

GASTROPODS SWALLOW SHELL RASPED

DURING HOLE BORING

Melbourne R. Carriker

College of Marine Studies,
University of Delaware
Lewes, Delaware 19958

Observations are reported on the ultrastructure
of shell material rasped by Urosalpinx cinerea
follyensis Baker from boreholes in the valves of
Mytilus edulis Linne and transported normally to
the stomach through the buccal cavity and esoph-
agus. Duration of the period of chemical activity
by the accessory boring organ and rasping by the
radula were determined with a valve model. Pel-
lets of shell raspings were removed from the
stomach and, after fracturing to reveal the in-
terior, and coating with metal, were studied with
the scanning electron microscope. Shell raspings
were compared with prisms and lamellae in frac-
ture surfaces of normal shell of M. edulis and shell
etched with ethylenediamine and sodium hypo-
chlorite to reveal the form of shell units clearly.

The study provided ultrastructural evidence for
the first time that U. cinerea swallows shell rasped
from the borehole during penetration of prey.
Both prisms and lamellae were identified in the
pellets removed from the stomach. Noticeable
dissolution of the organic matrix, and to some ex-
tent also of the mineral portion, of prisms was evi-
dent, features which facilitate removal of shell by
the snail during rasping. If the long axis of prisms
occurs parallel to the surface of the borehole, the
radula tends to rasp out long fragments of shell; if
prisms are placed at right angles to the surface, the

PROCEEDINGS OF THE NATIONAL SHELLFISHERIES ASSOCIATION

radula breaks prisms into small pieces. The envel-
ope of mucoid material which coats pellets un-
doubtedly reduces, or prevents, laceration of the
epithelium of the alimentary canal as shell
fragments pass down the tract. A gross approx-
imation of the percentage of shell in the borehole
which is rasped and swallowed during the process
of hole boring is 14 % .

THE INTERACTION OF WATER SOLUBLE

FRACTIONS (WSF) OF SOUTH LOUISIANA

CRUDE OIL AND DERMOCYSTID1UM

(LABYRINTHOMYXA) MAR1NUM AT

VARYING TEMPERATURES IN THE

AMERICAN OYSTER,
CRASSOSTREA VIRGINICA GMELIN

Keith Cooper

Marine Pathology Laboratory

Department of Animal Pathology

University of Rhode Island

Kingston, Rhode Island 02881

Sammy Ray and Jerry Neff

Moody College of Marine Sciences
and Maritime Resources
Texas A&M University
Galveston, Texas 77550

Over 500 oysters infected with D. marina were
exposed to 100% WSF crude oil in closed seawater
systems with water temperatures varying between
16°- 28c C. Elevated water temperature resulted in
greater mortality and significantly higher levels of
D. marina in infected oysters. Oysters exposed to
the WSF had significantly greater mortality and
decreased levels of D. marina than non-exposed
oysters. Concommitant temperature elevation and
exposure to WSF significantly increased mortality
and the rate of uptake of napthalenic hydrocar-
bons.

TETRACYCLINE AS A BIVALVE
SHELL MARKER

N. Dean Dey and Ellis T. Bolton

University of Delaware

College of Marine Studies

Lewes, Delaware 19958

Crassostrea virginica, Mercenaria mercenaria
and Mytilus edulis were exposed to the antibiotic
tetracycline in ambient sea water. The antibiotic
was dissolved in filtered sea water, to which algal
food was added. The animals were allowed to feed
on this mixture, which encouraged rapid shell
growth. The marking period lasted one week to
several months. Tetracycline was incorporated
concurrently with the rapid deposition of new
shell. The inlaid tetracycline fluoresces a vivid
yellow-orange under UV light (Mineralight,
254nm). Marking was vivid in Crassostrea and
Mercenaria and vague in Mytilus.

Marking was vague at 0.5 and 5.0 mg L"1 but
vivid at 25 to 200 mg L"1. No deaths or mor-
phological defects were noted at any concentra-
tion tested. The amount of inlaid tetracycline was
related to the quality of algal food. Algae species
known to be good food sources produced the
greatest incorporation of tetracycline. Marking of
Mercenaria larval and spat shells was visibly
bright at 25 and 50 mg L"1 and visibly evident at
0.5 and 5.0 mg L"1. under the dissecting micro-
scope. Experiments with five tetracycline ana-
logues showed that tetracycline phosphate com-
plex produced the best results with tetracycline
HCL, oxytetracycline, doxycycline and
minocycline producing progressively poorer
results.

The mark remains undiminished in vivo for at
least seven months, and its permanence is sug-
gested by structural changes to shell crystals on
the ultrastructural scale. The persistence of the
mark and its distinctive fluorescence suggest the
utility of tetracycline in studies of shell growth
and morphology and in field investigations. Com-
mercially, this technique could be used as an
identification, for example, by hatcheries to com-
bat poaching on leased grow-out grounds.

OYSTER REEF CULTIVATION
FOR CULTCH MATERIAL

William J. Eckmayer

Alabama Marine Resources Laboratory
Dauphin Island, Alabama 36528

A modified oyster dredge was used as a method
of utilizing existing buried shell for cultch. SCUBA

ABSTRACTS

and random m2 quadrats were used before and
after dredging to sample Bayou Cour Reef, Kings
Bayou Reef, and Shellbank Reef in Mobile Bay
and Bon Secour Bay, Alabama. The reefs were
dredged at a rate of 6.4 km/hour covering 0.4 ha
in one hour and 15 minutes.

The modified dredge was found to destroy half-
shell while exposing the half-shell resulting in an
increase in shell weight. The bottom was disrupted
and the exposed shell appeared to settle into the
bottom with a subsequent loss of relief followed
by an accumulation of silt.

Spat set increased following dredging, but loss
of relief makes this method unsatisfactory for reefs
over a soft substrate. Man-made or rehabilitated
oyster reefs on hard substrate may benefit from
this method.

MARKING CLAMS WITH RUBIDIUM1
Arnold G. Eversole

Clemson University
Department of Entomology and

Economic Zoology
Clemson, South Carolina 29631

Hard shelled clams, Mercenaria mercenaria,
were successfully marked with rubidium by rear-
ing seed clams in artificial seawater with an
aqueous solution of rubidium chloride. Elevated
levels of Rb* in samples of tissue were detected by
atomic absorption spectroscopy. Clams exposed
for 48 and 96 hours to 10.0, 1.0, 0.1 and 0.01 g/1
RbCl contained levels of Rb* significantly
higher than endogenous levels. Biological activity,
measured as siphon extension and survival of
clams, was not affected by the presence of RbCl at
concentrations less than 10.0 g/1. Also, sig-
nificantly higher levels of Rb* were present in
tissue for up to 3 weeks when clams were exposed
to 1.0 g/1 RbCl for 96 hours then transferred to
uncontaminated water.

Diatoms, Phaedactylus tricornutum, exposed
for 24,48 and 96 hours to 10.0, 1.0 and 0.1 g/1
RbCl had significantly higher levels of Rb* than
diatoms cultured without RbCl. Clams cultured
for 96 hours in vessels containing diatoms exposed
to 1.0 g/1 Rb CI had significantly more Rb* than

clams grown with unlabelled diatoms. Clams ex-
posed to 1.0 g/1 RbCl solutions with and without
diatoms contained levels of Rb* significantly
higher than those clams reared only with labelled
diatoms. No significant difference was detected
between clams grown with and without diatoms at
1.0 g/1 RbCl.

Mud crabs, Panopeus herbstii, were offered Rb*
labelled clams for 96 hours then sacrificed or
transferred to containers with unlabelled clams for
7 days. Control crabs were fed unlabelled clams
and sacrificed at 96 hours and 7 days. Fecal
strands of experimental crabs had elevated levels
of Rb* with a peak at approximately 132 hours.
Four tissues dissected from control and experimen-
tal crabs were analyzed and significantly higher
levels of Rb* were found in the hepatopancreas of
experimental crabs after the first 96 hours. No ap-
parent difference was detected at 7 days.

This study was supported by the South Carolina Experiment
Station and Clemson University Faculty Research Commit-
tee.

SUSPENSION CULTURE OF EUROPEAN
OYSTERS (OSTREA EDUL1SL.)

Reg Gillmor

Ira C. Darling Center

University of Maine at Orono

Walpole, Maine 04573

Operations have appeared along the coast of
Maine during the past few years for the culture of
European oysters. Suspension techniques are used
for the grow-out of cultchless, hatchery-reared
seed, and suspension systems most often involve
one or another variation on the Japanese long- lin-
ing theme. The first system to appear commercial-
ly employs floating modules consisting of stacks
of wooden-framed plastic mesh trays short-
tethered to a long hauser line. These are tended
from a raft which can hoist modules aboard for
servicing — cleaning, grading, etc. — one at a time.
A second system was recently introduced which
makes use of culture nets imported from Japan
where they were developed for the rearing of pearl
shells and scallops. In this system the gear is in-

PROCEEDINGS OF THE NATIONAL SHELLFISHERIES ASSOCIATION

dividually buoyed and suspended, either near the
surface or at mid-depth, beneath a long line. A
service raft is also utilized and in this case there ex-
ists the possibility of batch-servicing a number of
net modules simultaneously. A third technique
has appeared for nursery grow-out in well pro-
tected areas. The culture unit is a rectangular,
wooden-framed tray enclosed with plastic mesh
on both top and bottom. These are strung together
end to end, floated in rows, and flipped regularly
so that each side is alternately exposed and
submerged, a procedure which controls fouling.
The equipment and methods of several oyster
farms are illustrated and discussed indicating the
varying approaches to common problems such as
retrieval and resuspension of modules, prevention
and removal of fouling, overwintering and others.
The development of the Maine oyster aquaculture
industry as a whole is briefly reviewed.

GROWTH RESPONSES OF EUROPEAN

AND AMERICAN OYSTERS

(OSTREAEDULISL.

AND CRASSOSTREA VIRGINICA G.)

TO INTERTIDAL EXPOSURE

Reg Gillmor

Ira C. Darling Center

University of Maine at Orono

Walpole, Maine 04573

In view of the use which is made of the intertidal
zone in the rearing of oysters in other areas of the
world (e.g., Japan, New Zealand) studies were
undertaken to determine its potential usefulness to
the culture of European and American oysters in
Maine. As part of a seed "hardening" experiment,
spat were suspended at 1 subtidal and 5 intertidal
levels (9-49% mean aerial exposure time). Mon-
thly instantaneous growth (whole dry weight)
rates (k) indicated American oysters to be "break-
ing even" with exposure; i.e., over the range of
levels tested a given percentage change in immer-
sion times was matched by an equal change in k so
that growth relative to immersion time was ap-
proximately the same at all levels. The k vs. ex-
posure curve for European oyster seed was also
linear but differed in having a more rapid decline
in growth with increasing exposure. A similar pat-

tern of growth was exhibited by yearlings of the 2
species suspended for 5 months at 10 levels
centered more or less on mean low water. Because
of the closer spacing and more restricted range of
exposure levels (0-30%) in this experiment,
however, a better resolution of the growth
response at the lower levels of exposure was possi-
ble, and an interesting feature of European oyster
growth not distinguishable in the seed study
emerged: Growth at levels of exposure up to
10-12% equalled that of subtidal oysters, in-
dicating that growth relative to immersion time
was actually greatest in the groups exposed at low
levels. At higher levels k values declined rapidly.
Growth of American oysters again appeared to
correspond with immersion time in a one-to-one
fashion. The O. edulis result suggests a potential
use of the lower intertidal for the "market
hardening" — conditioning for prolonged valve
closure — of European oysters to extend their shelf
life, a problem which has been troubling Maine
aquaculturists. Such a procedure need not entail
any loss of growth.

THE ONSHORE SURF CLAM RESOURCE

ALONG THE SOUTHERN NEW JERSEY

COAST

Harold H.Haskin

Oyster Research Laboratory

New Jersey Agricultural Experimental Statio)i

and Department of Zoology

Rutgers University
New Brunswick, New Jersey

With the general decline of the offshore surf
clam beds under increasing dredging pressure over
the past decade, an increasing proportion of the
New Jersey catch has been taken from the inshore
beds, close to the beaches of Atlantic and Cape
May Counties. This shift in fishing effort has caus-
ed concern for the maintenance of the inshore
populations and, since 1972, has led to studies of
population size, distribution, recruitment and
growth.

During this period the standing stock within the
three-mile limit has been declining continuously
and is now estimated at less than 4-million

ABSTRACTS

bushels. In general the more dense populations are
close to the beaches and, within the three-mile
limit, decrease in density with distance offshore.
The clams also show two distinct gradients in size:
(1) smaller clams inshore; (2) smaller clams up the
shore in the stretch from Cape May to Beach
Haven inlet.

Over several summer seasons settling of juven-
iles has been general in the inshore area with den-
sities ranging up to several hundred per square
meter. Early mortality rates, however, have been
high and by end of summer young of the year are
virtually non-existent. Principal predators include
Limulus. Ovalipes and Pagurus. No substantial
recruitment has occurred in the past five years.

MORTALITY PATTERNS AND DISEASE
RESISTANCE IN DELAWARE BAY OYSTERS

Harold H. Haskin and Susan E. Ford

Oyster Research Laboratory

New Jersey Agricultural Experimental 5tatio>i

and Department of Zoology

Rutgers University
New Brunswick, Neio Jersey

Since 1964, 29 groups of oysters have been
laboratory-bred for resistance to kill by Minchinia
nelsoni, then selected and tested for survival in en-
zootic waters in Delaware Bay. Survival at the end
of a 33-month test period of four filial generations
of selected stocks has been compared to that of un-
selected groups. Compared to 16 groups of suscep-
tibles the survival ratio of F, resistants is 4.4; this
ratio increases to 5.0, 6.6 and 8.9 for F:, F, and F4
respectively. Native set originating from parents
selected on planted grounds in the lower bay, have
a cumulative kill falling between susceptibles and
Fi resistants, with a survival ratio of 2.9 compared
to the unselected stocks.

Differential mortality ratios are established dur-
ing exposure to the first complete summer infec-
tive period and are maintained with little variation
for the remainder of the test period. Despite a
plateauing of cumulative mortality curves for all
stocks after the initial kill, seasonal mortality rates
remain higher for susceptibles than for resistant
groups after nearly three years of selection.

Non-predation kill on Delaware Bay native seed
stocks planted on low bay leased grounds during
the past 12 years has generally demonstrated sur-
vival comparable to laboratory-reared resistant
groups.

THE OYSTER INDUSTRY
OF VIRGINIA 1931 to 1975

Dexter S. Haven, William J. Hargis, Jr.
and Paul C. Kendall

Virginia Institute of Marine Science
Gloucester Point, Virginia 23062

This study investigates the cause or causes of
the decline in productivity of Virginia's oyster in-
dustry over the years and especially the catas-
trophic decline since 1960. Included in this report
are detailed studies on landings and oyster densi-
ty, a documentation of the decline in spatfall in
many areas since 1°60, reviews of predators and
diseases, repletion activities, laws and other
aspects.

The principal reason for the decline since I960
has been the direct or indirect impact of MSX, but
other factors associated with degradation of the
environment may also have operated. In many in-
stances rising labor costs and antiquated tech-
nology have prevented a recovery of the industry.

Recommendations for improving the industry
are given.

AGE, GROWTH, REPRODUCTION

AND DISTRIBUTION OF THE BAY

SCALLOP,

AEQU1PECTEN IRRAD1ANS

1RRADIANS (LAMARCK).

IN THREE EMBAYMENTS

OF EASTERN LONG ISLAND, NEW YORK,

AS RELATED TO THE FISHERY

Mary T. Hickey'

Department of Marine and Environmental Science

C. W. Post Center. Long Island University

Greenvale. New York 11548

Bay scallops are an economically important
fishery on eastern Long Island. The bay scallop

PROCEEDINGS OF THE NATIONAL SHELLFISHERIES ASSOCIATION

populations in three embayments in the Town of
East Hampton, N.Y., were studied for weight,
growth, and condition of the adductor muscle,
reproduction, shell growth, abundance and
distribution.

The spawning effort is maximized at the expense
of other functions. Spawning occurs primarily in
tune and is temperature related. The adductor
muscle index and condition decrease during gonad
maturation and spawning, and shell growth near-
ly ceases during the reproductive period. The
greatest rate of weight gain of the adductor muscle
and greatest shell growth occur during the post-
spawning period, July through October.

Commercially acceptable growth appeared to
be density and depth related. Modal shell length of
the harvestable year class was 60-65 mm at the
beginning of the fishing season in October. State
and local minimum size regulations were evalua-
ted on a biological basis and management recom-
mendations were discussed.

Present address: 4415 Independence St., Rockville. Md.
20853.

OYSTER SETTING - EVOLUTION OF
COMMERCIAL HATCHERY TECHNIQUE

Herbert Hidu

Richard D. Clime

Samuel R. Chapman

Ira C. Darling Center

University of Maine

Walpole, Maine 04573

Cultchless setting has obviously revolutionized
hatchery economics. Bill Budge's development has
led to a variety of proprietary and apparently
non-proprietary approaches to the process.
Ultimate optimization in cultchless setting must
depend on a complete understanding of physiolog-
ical and behavioral responses at setting. It is clear
that oyster larvae can delay metamorphosis and
set in response to environmental stimuli. Our ex-
periments indicate that the setting response is
released by rapid temperature increases, water-
borne pheromones from adult oysters, and an
unknown property associated with calcium car-
bonate of shell. All are used to advantage in an ef-

ficient cultchless process. Several calcium
carbonate related materials appear to be stimula-
tory including tropical beach sand, foraminiferal
sand (we thank Mr. Thomas W. Dignes for sug-
gesting the use of foraminiferal sand as a cultch
material), polished marble and marble chips. It is
possible to orient larvae with hinge-side upper-
most on vertical polished marble slabs thus in-
creasing the efficiency of removal without dam-
age. A complete understanding of the reponse to
calcium carbonate may allow us a system of
oyster metamorphosis in the absence of substrate.

AN OYSTER FAMILY TREE:
ANCESTRY OF CRASSOSTREA VIRG1NICA

Sewell H. Hopkins

Department of Biology

Texas A&M University

College Station, Texas 77843

A hypothetical family tree of oysters is
presented, based on the authoritative text of H.B.
Stenzel ("Oysters," volume 3 of 3, Part N,
Bivalvia, Mollusca 6, Moore's Treatise on In-
vertebrate Paleontology, 1971). However, I do
not believe that our oyster descended from the
giant Eocene "Crassostrea" gigantissima as some
geologists argue (Sohl and Kauffman, 1964, and
others). As an ancestor for our oyster I prefer
Crassostrea glabra (Meek and Hayden, 1857).
This species was abundant in widely separated
parts of the huge brackish Laramie Sea that ex-
tended across the interior of Western North
American, from Canada to Mexico, in very late
Cretaceous time. It was associated with a few
other species of marine origin (species of Anomia,
Brachidontes and Corbula, along with some
species of genera which have both marine and
fresh-water affinities: Corbicula, Neritina,
Melania, and other). In other parts of the same sea
there were many species of genera which are now
found only in fresh water, indicating that salinity
must have been very low. C. glabra seems to have
been a true Crassostrea, usually lacking the
marginal denticles that Stenzel called "chomata,"
and was very similar to living Maryland oysters of

ABSTRACTS

the deep-water type. Descent from an oyster of a
low-salinity brackish sea may account for the fact
that C. virginica tolerates lower salinity than any
other living oyster. C. gigantissima, besides hav-
ing chomata when young and thus not being a
Crassostrea by Stenzel's definition, was associated
with many marine species as you would expect if it
grew in salty coastal lagoons.

BACTERIOLOGICAL STUDIES OF
LONG ISLAND SHELLFISH HATCHERIES1

Louis Leibovitz

Department of Avian and Aquatic Animal

Medicine

New York State College of Veterinary Medicine

Cornell University, Ithaca, N.Y.

High concentrations of bacteria in shellfish
hatchery media have been reported as a cause of
larval mortality. This study was undertaken to
characterize the dominant bacterial flora of the
Long Island shellfish hatcheries. Although the
study was initiated at a single hatchery during
1972, the current report covers a three-year period
(1974-1976) and includes 5 hatcheries. Bacterio-
logical samples from sick and healthy oyster and
clam larval cultures and their ingredients were
taken at a standard working dilution onto Plate
Count Agar media with synthetic sea salts. Each
cultural sample was replicated in triplicate. The
hatchery ingredients samples included incoming
ultraviolet treated and untreated bay and well
water, stock algal cultures, and pooled algal
cultures. Samples were taken throughout the year
at regular monthly intervals. Qualitative and
quantitative counts were made of the dominant
populations of each culture and isolated colonies
were identified as pure cultures.

A total of 1,279 cultures were taken and 710
pure bacterial isolates were identified. Sixty-six
percent of all bacteria isolated and identified from
intake water samples were gram negative, and
15.7 percent were gram positive. Well water had a
higher percentage of gram positive organisms than
did bay water intake. Thirty-three percent
Pseudomonas, 10.4 percent Flavobacter or
Cytophaga, 8.7 percent Acinetobacter, 4.9 per-
cent Aeromonas, 3.8 percent Enter obacteriacea,

3.2 percent Vibrio and 1.5 percent Achromobacter
spp. were the dominant gram negative isolates
found in all water sampled. Well water counts
were lower but contained a higher percentage of
Aeromonas, Vibrio, and Flavobacter or
Cytophaga and less Enterobacteriacea than did
bay water. Ultraviolet treatment had no effect on
bacterial counts of hatchery water intake. Stock
algal cultures were frequently contaminated with
a wide variety of bacteria. The percentage of
Acinetobacter and Flavobacter or Cytophaga spp.
increased in algal cultures. Sick or dying oyster
larval cultures are characterized by a sharp de-
crease in the percentages of Pseudomonas,
Flavobacter or Cytophaga, Acinetobacter and
Enterobacteriacea spp. and a rise in percent gram
positive bacteria. Sick clam larval cultures were
associated with a drop in the percentage of Flavo-
bacter or Cytophaga, Aeromonas, and
Enterobacteriacea spp. The percent of unidentified
and lost bacterial cultures increased in sick oyster
and clam larval cultures. Each hatchery larval
culture media had its own distinctive bacterial
flora. High bacterial counts were associated with
warm weather, increased storage and culture time,
and high organic content. The frequency and dis-
tribution of Vibrio spp. during an outbreak of
vibriosis is reported. Water quality studies were
conducted during the study. The usefulness of
routine bacteriologic sampling for diagnostic pur-
poses is discussed.

1. This research was sponsored by the New York Sea Grant
Institute under a grant from the Office of Sea Grant. Na-
tional Oceanic and Atmospheric Administration (NOAA),
U. S. Department of Commerce.

WATER QUALITY STUDIES OF LONG ISLAND
SHELLFISH HATCHERIES '

Louis Leibovitz and John Hamlin Gordon II

Department of Avian and Aquatic

Animal Medicine

New York State College of

Veterinary Medicine

Cornell University, Ithaca, N.Y.

Since the health of shellfish larvae and the ef-
ficacy of shellfish hatchery production is depend-

PROCEEDINGS OF THE NATIONAL SHELLFISHERIES ASSOCIATION

ent upon the characteristics and stability of the
water supply, a study of the water quality of bay
and well water intakes of 5 Long Island shellfish
hatcheries was undertaken to define the cycle and
range of water quality changes throughout a pro-
duction year. Samples were taken at regular
monthly intervals and included measurements for
ammonia, nitriate, nitrate, orthophosphate, total
organic phosphate, total inorganic phosphate,
dissolved oxygen, pH, salinity and temperature.

Ammonia well values ranged from a low of 0.5
to a high of 5.2 and a mean of 1.67 mg/liter. Bay
intake ammonia values ranged from 1.7 to 7.0 and
a mean of 4.52 mg/liter through the year. Am-
monia values rose through the spring and summer
months with a sharp decline at the end of the year
during early winter. A precipitous short-term
drop in ammonia levels in July was associated
with an outbreak of vibriosis and high larval mor-
tality at one hatchery.

Nitrate values ranged from 0.5 to 5.0, mean
1.77 mg/liter for well; and 0.5 to 6.1, mean 4.52
mg/liter for bay intake. During spring and sum-
mer months low levels of nitrate were found,
followed by a sharp increase in fall and winter.

Orthophosphate levels ranged from 0.03 to
0.095, mean 0.05 mg/liter for well water and 0.04
to 0.40, mean 0.186 mg/liter, for bay intake. In
the presence of oxygen, orthophosphate and iron
levels are interrelated. An extremely high short-
term orthophosphate level was associated with
disease at one hatchery utilizing fossil fuel thermal
effluent.

Iron levels in bay water increased markedly in
the spring of the year and decreased later. Iron
levels in well water were low and at a stable level.
Copper fluctuated throughout the year, but were
always higher than reported for ambient oceanic
levels.

Well intake had lower pH values than bay in-
take. Both became more alkaline during spring
and summer, and more acid during fall and winter
months.

More work is needed to select and define the
criteria for water quality tests at shellfish hatch-
eries.

1 This research was sponsored by the New York Sea Grant
Institute under a grant from the Office of Sea Grant, Na-
tional Oceanic and Atmospheric Administration (NOAA),
U.S. Department of Commerce.

A COMPARISON OF HINGE-LINE

MORPHOGENESIS IN LARVAL SHELLS OF

MYTILUS EDUL1S L. AND

MODIOLUS MODIOLUS (L.)

Richard A. Lutz

Yale University

Department of Geology and Geophysics

New Haven, Connecticut 06520

Optical and scanning electron microscopic ex-
amination of laboratory reared cultures of larval
Mytilus edulis (blue mussel) and Modiolus
modiolus (northern horse mussel) revealed similar
hinge-line morphogenesis (straight-hinge stage
through metamorphosis) in both species. The
hinge apparatus (provinculum) of both mytilids
increased in size and complexity throughout larval
development, with progressive lateral thickening
characteristic of the family Mytilidae. The number
of "teeth", while highly variable between in-
dividuals with similar shell dimensions, increased
significantly with both total shell and provin-
culum length. Ultrastructural studies of the teeth
revealed marked ridged structures which became
increasingly apparent with larval growth. In
neither species did lateral teeth develop prior to
settlement and metamorphosis.

Significant differences at the population level
were found between Mytilus edulis and Modiolus
modiolus upon regression and quantitative com-
parison of each of the following: larval length vs.
provinculum length; larval width vs. provinculum
length; provinculum length vs. number of teeth;
and larval length vs. number of teeth. Such dif-
ferences should prove useful in discrimination of
these two mytilids within the plankton.

CULTURE OF THE SEA SCALLOP,

PLACOPECTEN MAGELLANICUS (GMELIN)

IN NEWFOUNDLAND

K.S.Naidu

Fisheries and Marine Service

Fisheries and Environment Canada

3 Water Street

St. John's, Newfoundland

A1C1A1

ABSTRACTS

Techniques used to collect naturally-produced
sea scallop (Placopecten magellanicus) spat using
artificial substrates and their subsequent growth in
hanging culture at a near-shore locality in New-
foundland are described.

Of the various substrates employed polyethy-
lene film enclosed in onion bags appeared to be the
most suitable. Using this substrate the mean
number of live scallop spat collected increased
with depth to about 12 m; deeper than this, the
numbers settling decreased. Collectors suspended
in less than 8 m harboured considerable numbers
of starfish. Numbers of live spat and starfish in
collecting units were inversely correlated. The
mean size (±1 S.D) of live spat (dorso-ventral
axis) at the time of collection was 12.4 ±0.81 mm
with a range of 5.0 to 19.1mm. There was a slight
but significant increase in size with depth, the dif-
ference in size being approximately 1.0 mm over
the 12 m range sampled.

Growth of scallops in suspended culture was ex-
ceptionally good. Preliminary results indicate that
shell heights of 12, 24, 36, 48 and 60 month-old
animals to be in the order of 36, 66, 80, 95 and 107
mm respectively. Corresponding shell heights of
wild scallops from the sea bottom in the same area
were x, 27,46, 66 and 85 mm (x, 12 month-old
scallops, were not represented in the study). Mor-
tality is approximately 5% per annum. Animals
under two years appear to sustain higher mor-
talities than those above it.

The relatively sedentary nature of the animal
opens up the possibility of resource enhancement
of the species through sea ranching the coastal
zone. This less expensive but longer route is being
examined as well.

ENGINEERING CONSIDERATIONS IN THE

DESIGN OF

OYSTER DEPURATION PLANTS

Bruce J. Neilson

Virginia Institute of Marine Science
Gloucester Point, Virginia 23062

Oyster depuration studies were conducted using
four commercial size tanks with varying en-
vironmental factors and initial bacterial levels. All
four tank designs were suitable for the process,

but two were superior. The primary design fea-
tures which appear to be important are the resi-
dence time of the water and the circulation pattern
within the tank. Fecal coliform levels in the water
were observed to rise as soon as the oysters were
placed in the tank. Depuration occurs more rapid-
ly if the bacteria released by the shellfish are rapid-
ly removed from the tank. The time for a 90%
reduction in concentration of dye injected into the
tank was found to be roughly twice the theoretical
residence time, which is obtained by dividing the
total volume by the flow rate.

The residence time may be decreased by increas-
ing the flow of water. An alternative method is to
increase the number of oysters held in the tank.
Tests showed that depuration was equally success-
ful in identical tanks holding 1.8 and 3 bushels of
oysters if the flow of water per bushel of oysters
was the same for both tanks.

Good circulation in the tank is needed to pre-
vent dead areas which could become oxygen de-
pleted. Dye tests showed that the residence time
was greatly reduced when a water pump was used
to increase the flow within the tank. Air lift pumps
can accomplish the same result. If the system is
properly designed, the resulting current will be
smooth and gentle and will not resuspend biode-
posits.

OIL AND THE OYSTER IN DELAWARE BAY

George S. Noyes,

Harold H. Haskin,

and Cindy Van Dover

Oyster Research Laboratory

New Jersey Agricultural Expt. Station

and Department of Zoology

Rutgers University

Potentially hazardous effects of petroleum and
its derivatives on an economically important
population of the American oyster, Crassostrea
virginica, were investigated to assist development
for the Delaware estuary, of more precise water
quality standards, compatible for both industry
and survival of oyster beds.

Adult and larval oysters were chronically ex-
posed to crude and refined oils adsorbed onto fine
kaolin clay. Threshold concentrations for mor-

PROCEEDINGS OF THE NATIONAL SHELLFISHERIES ASSOCIATION

talities and relative toxicities for different oils were
determined.

Adult oysters exposed to 0.3 ppm Nigerian
crude showed mortalities twice those of controls.
No. 2 fuel oil was approximately twice as toxic as
Nigerian crude, which in turn was twice as toxic as
Iranian light crude.

Larvae, cultured in natural seawater, developed
and metamorphosed in control treatments, but
showed increasing mortality, delay in develop-
ment, and inhibition of metamorphosis at and
above concentrations of 0.5 ppm Nigerian crude
oil. No. 2 fuel oil was highly toxic to larvae at con-
centrations as low as 0.25 ppm. Larvae did not
show greater sensitivity to oils when compared to
adults.

THE ROLE OF URONEMA

MARIN UM (PROTOZOA)

IN OYSTER HATCHERY PRODUCTION

Linda Plunket

Ira C. Darling Center

University of Maine at Orono

Walpole, Maine 04573

In Maine's hatchery production of oysters,
significant mortalities at the early juvenile stage
have been associated with ciliate protozoan in-
festations. The predominant ciliate was isolated
from live infested oysters in the Spring of 1974 and
was identified as Uronema marinum. Feeding-type
experiments were carried out to determine what
food source this ciliate was utilizing in the tank en-
vironment. Uronema marinum was found to be a
bacteriophage and not a histophage; thus, the high
mortalities accompanying the early juvenile stage
cannot be primarily attributed to the ciliate in-
festations.

The survival and growth of hatchery reared
bivalves have been investigated in a system of
fiberglass raceways through which seawater was
continuously pumped. Flow rates of 50 to 60
1/min were maintained in tanks 10 m X 1.3 m with
variable depths. The bay scallop, Argopecten irra-
dians, was successfully grown in the raceways
from a size of 5 mm. Varying raceway depth be-
tween 7.5 and 30 cm had no effect on scallop
growth. Scallops at stocking densities of 5, 10, 20
and 40 1/raceway and culled back to these den-
sities at bi-weekly intervals grew at rates inversely
proportional to population size. Scallops stopped
growing when the water temperature declined to
10°C. The surf clam, Spisula solidissima, was
successfully grown in the system from a starting
size of 1 mm. Spisida smaller than 20 mm grew
equally well in sand and without a substrate. Surf
clams larger than 20 mm grew faster in a sand
substrate than without and some shell abnormali-
ties were observed in clams grown without
substrate. Surf clams exhibited a growth rate in-
versely proportional to stocking density for
biomasses of 1, 4 and 8 1/raceway. The excellent
growth rate of these bivalve species in raceways
suggests that the use of this system may be a
valuable step in the production of shellfish seed.

STATUS REPORT ON THE COMMERCIAL

BLUE CRAB FISHERY

OF THE CAROLINAS AND GEORGIA

R.J. Rhodes1,
M. Wolff2, J.L. Music3

1. South Carolina Wildlife

and Marine Resources Department

Division of Marine Resources

Charleston, S.C.

THE USE OF PUMPED RACEWAY SYSTEMS

FOR THE INTERMEDIATE

GROW-OUT OF HATCHERY REARED

BIVALVES

Edwin W. Rhodes and Ronald Goldberg

U.S. Department of Commerce - NO A A

National Marine Fisheries Service

Northeast Fisheries Center

Milford, Connecticut 06460

2. North Carolina Department of

Natural and Economic Resources

Division of Marine Fisheries,

Morehead City , N.C.

and

3. Department of Natural Resources,

Coastal Resources Division

Brunswick, Georgia

ABSTRACTS

The annual landings, operating unit data, and
ex-vessel price for the commercial blue crab
(Callinectes sapidus) fisheries in North Carolina,
South Carolina and Georgia between 1960 and
1976 were analyzed to document recent trends in
this fishery and discuss possible factors causing
the decline in landings since 1970. Between 1970
and 1976, the total annual landings of blue crabs
in the Carolinas and Georgia have declined at an
average rate of 2 million pounds per year (1970
landings = 35 million pounds), while 3 thousand
traps per year were added to the fishery between
1970 and 1975.

The ex-vessel price for blue crab has increased
from $.05 per pound in 1970 to $.11 per pound in
1976 with an increase of 20% in the adjusted price
per year compared to 1970. This trend suggests a
quantity-effect dominant ex-vessel price function.
Inaccuracies in the N.M.F.S. reporting system and
the lack of recreational and commercial harvesting
catch-effort data severely limits the analysis of the
current trends. Future trends in the harvesting sec-
tor and management research considerations will
be discussed.

THE DEVELOPMENT OF THE HINGE LINE

IN TROPICAL MUSSEL

LARVAE OF THE GENUS PERNA

Scott E.Siddall

University of Miami

School of Marine and Atmospheric Science

4600 Rickenbacker Causeway

Miami, Florida 33149

There is confusion in the literature regarding the
synonomy of several species of the genera Perna
and Mytilus. To resolve this problem, I reared lar-
vae of Perna perna from Venezuela and Perna
viridis (= Mytilus viridis) from the Philippines
through metamorphosis. All living material was
quarantined in the laboratory. The results of my
scanning electron microscopic examination of
these larvae and the larvae of Mytilus edulis clear-
ly differentiate hinge line development in the two
genera. In both Perna species at optimal tempera-
tures and salinities, hinge teeth are well developed

as early as 15 hours after fertilization. Shell length
to height ratios decrease as development proceeds
with no significant differences between the
species. As the larvae approach metamorphosis,
the central hinge teeth become more numerous
and develop columnar structures. The provin-
culum broadens laterally in larvae of both genera.
Approximately 20 days after fertilization, a series
of larger hinge teeth lateral to the central teeth
develops in both P. perna and P. viridis in con-
trast to larvae of the genus Mytilus. Differences in
the crystal structure between the lateral and cen-
tral teeth are apparent. I have examined metamor-
phosing larvae of the only other member of the
genus, Perna canaliculus from New Zealand and
found similar lateral hinge teeth. The results of my
work support the placement of Mytilus viridis in
the genus Perna.

AGE AND MORPHOMETRIC VARIATION
IN SUBTIDAL POPULATIONS OF MUSSELS

Robert S. Steneck1,
Richard A. Lutz2. and Robert M. Cerrato2

department of Paleobiology
Smithsonian Institution
Washington, D.C. 20560

'Department of Geology and Geophysics

Yale University

New Haven, Connecticut 06520

The structure of two subtidal syntopic mussel
populations (Mytilus edulis and Modiolus
modiolus) was investigated. A total of 703 mussels
were collected along two 10-meter transects at
depths of 5 and 10 meters off Rutherford Island,
Maine. Population densities for Mytilus of
50.4/m2 and 144. 4/m2 were recorded at 5 and 10
meters, respectively. Population densities of
Modiolus were 71.2/m2 at 5 meters and 15.2/m2 at
10 meters.

A total of 263 Mytilus specimens of all sizes
were randomly selected and ages accurately deter-
mined through examination of annual patterns on
acetate peels of sectioned shells. The maximum
age (24 years) encountered within the population
is considerably greater than that reported to date

PROCEEDINGS OF THE NATIONAL SHELLFISHERIES ASSOCIATION

within the literature. The age-frequency distribu-
tion for the sampled population showed marked
cyclic abundance patterns with 49.4% of the
population restricted to yearclass multiples of 7.
This observed periodicity may be a reflection of a
regularly occurring natural event such as a preda-
tor-prey oscillation.

Classical modal analysis of size frequency
distributions cannot differentiate between annual

recruitment and cyclic abundance patterns with
periods greater than 1 year. The potential for fre-
quent interpretive errors by ecologists and paleon-
tologists using modal analysis to infer age struc-
ture is discussed.

Modiolus population structure is inferred by
comparing crustose coralline incrustation rates for
Mytilus of known ages with incrustations on
Modiolus.

ABSTRACTS

NSA PACIFIC COAST SECTION

BREEDING DISEASE RESISTANCE INTO THE
PACIFIC OYSTER

fohn H. Beattie', William K. Hershberger',
Kenneth Chew1 and Conrad Mahnken2

1 University of Washington

College of Fisheries

Seattle. Washington 18105

and

'National Marine Fisheries Service

Seattle, Washington

Since the 1970s, the University of Washington,
College of Fisheries has been involved in a
cooperative study with the National Marine
Fisheries Service and the Washington State
Department of Fisheries investigating the causes of
Pacific oyster (Crassostrea gigas) summer mor-
talities. Studies have included laboratory testing
using elevated water temperatures, nutrient
enrichment of sea water, and isolation of im-
plicated bacteria from moribund oysters to
simulate summer conditions.

During the past three years, the College of
Fisheries has also developed a selective breeding
program as an effort toward the prevention of
future kills through the introduction of disease
resistant stocks. Survivors of laboratory high
temperature challenges (above 18 C) were used as
parents to produce potentially resistant F, families
at the Poulsbo, Washington Sea Farms hatchery
during 1974 and 1975. Challenges of these stocks
in October, November, and December of 1976 in-
dicated two families to be significantly more resis-
tant to mortality conditions than imported
Japanese stocks.

Thirty additional F, families were produced
during 1976. F2 families have been produced in
1977 using the 1974 and 1975 F, stocks as parents.

Some of these 1975 families have been planted in
areas of historic summer mortalities in
Washington (Rocky Bay and Mud Bay). Represen-
tative stocks of the 1975 F2 test animals have been
given to two hatcheries for large-scale production
and testing. Tissues are also being examined elec-
trophoretically for specific genetic information.

OYSTER LARVAE MORTALITY IN
SOUTH PUGET SOUND

RickD.Cardwell

Washington Department of Fisheries

Salmon Research and Development

Box 600, Pt. Whitney Road

Brinnon Washington 98320

In the summer, particularly late summer,
marine waters from many areas of the Puget
Sound basin as well as Willapa Bay are found to
kill Pacific oyster (Crassostrea gigas) embryos and
larvae when samples of these waters are brought
to the laboratory and used to culture newly- fer-
tilized embryos for 48 hours. Oyster larvae mor-
tality can occur in waters unaffected by point and
non-point sources of pollution and is most severe
and widely distributed in several inlets in inner-
most Puget Sound (SPS).

More than 15 years of biomonitoring the marine
waters of SPS for acute toxicity to oyster embryos
has disclosed the following: larval mortality is a
seasonal phenomenon; in Budd and Eld Inlets, ap-
preciable (>20%) mortality commences around
June, peaks in late August to early September, and
subsides in late October. The scope and severity of
the mortality varies greatly between inlets, with
Eld Inlet causing the highest average mortality,
and Budd, Case, Totten, Carr, and Hammersley
Inlets causing lesser mortality, respectively.

PROCEEDINGS OF THE NATIONAL SHELLFISHERIES ASSOCIATION

Within a particular inlet, mortality increases from
the entrance to the head and varies significantly
with water depth. Waters 10 to 30 ft in depth
usually are more toxic than those at the surface.

The evidence suggests that the toxicity is caused
by toxic metabolics of natural planktonic consti-
tuents. Although more than one organism is im-
plicated, recent evidence suggests that high den-
sities of the dinoflagellate Ceratium fusus can ex-
plain a significant percentage of the variation in
larval mortality. Removal of most of the Ceratium
by low pressure— not vacuum— filtration through
a 10/^m screen greatly reduces toxicity.

Work is underway to define the identity of some
of the suspected toxic agents and to relate varia-
tions in circulation, water quality, and biological
productivity between inlets to observed larval
mortality.

Research has been supported in part by the Marine
Ecosystems Analysis (MESAl-Puget Sound Project of
NOAA.

HELICOPTER CRABBING

Darrell Demory

Oregon Department of Fish and Wildlife

Newport, Oregon

The newest inovation in crab fishing was off to
a flying start off the southern Oregon coast early
in 1977 when a helicopter was used to pull oversiz-
ed crab pots. The helicopter angled with a 6-foot
grappling hook on a 25-foot line. The 110-foot
double-buoyed pot line was snagged and the 6-
foot wide pot was pulled out of the ocean and
flown to the landing site. The crabs were removed
from the pot and the pot was rebaited and flown
back to the fishing site. A loop of line attached to
a small hook that was in turn attached to the grap-
pling hook enabled the pilot to release the pot by
putting slack in the line after the pot hit the sea-
bed.

Small or female crabs caught in this manner
were flown back to the water in a dump container
that was lowered to the water where it was tipped
over, sliding the crabs out.

Claims by some conventional crab fishermen
that small crabs were being "rained across the
beach" proved to be grossly exaggerated. Several

days of observation by Department of Fish and
Wildlife staff and the State Police showed that the
operation damaged very few crabs and was pro-
bably less damaging than the boat fishery.

Although only 40 pots were fished, some boat
fishermen fear an adverse economic impact on the
fishery. The manager of the Oregon All Coast
Fishermen's Marketing Association stated publicly
that helicopter crabbing is too efficient .

Two helicopter operations made landings in
1977, but it is possible that others may soon
become interested.

DISEASE CONTROL IN A MOLLUSCAN
SHELLFISH HATCHERY

Richard A. Eissinger

International Shellfish Enterprises, Inc.
Moss Landing, California

The emphasis in shellfish hatchery disease con-
trol has been on treatment rather than prevention.
This paper presents several operating concepts on
disease prevention management employed at In-
ternational Shellfish Enterprises in Moss Landing,
California.

Brood stock must be carefully and frequently
selected and histologically monitored to assure the
customer that he will receive a disease, parasite
and predator free seed product.

Routine sanitation practices through use of
isolated culture systems, the careful avoidance of
cross-contamination through sterilization of all
culture implements, and the routine disinfection of
the hatchery water delivery system will help to
prevent transfer of disease from one hatchery
location to another.

Daily monitoring for the presence of bacterial
pathogens is extremely important in order to
discover a disease before it becomes un-
manageable. Monitoring becomes especially im-
portant in screening algal cultures before they are
used for feeding.

Antibiotic therapy is used only as a last resort to
control disease. When using antibiotics, an effec-
tive choice of antibiotic can only be made with the
use of antibiotic susceptibility testing, and proper
dosages can only be determined through the use of
tube dilution sensitivity testing.

ABSTRACTS

Sanitation and bacterial monitoring can con-
tribute significantly to stabilizing shellfish hatch-
ery production output and helps to assure the
customer that the product he buys is of the best
possible quality and highest survival value.

SQUAXIN ISLAND MANILA CLAM
RESEEDING STUDIES

]im Glock

University of Washington

College of Fisheries
Seattle, Washington 98105

As a part of a series of studies to determine the
future potential for reseeding beaches with small
clam seed, Manila clams (Venerupis japonica) seed
clams were planted at Squaxin Island, (Puget
Sound) in May 1976 and have been monitored for
growth and recovery. Various protective mechan-
isms tested in this study have demonstrated dif-
ferential effects on recovery rates. DuPont Vexar
plastic netting, used at different sites, maintained
recoveries of 75%, 97%, and 29% after 15 mon-
ths. Preliminary migration studies have -shown
that the clams move on the beach after planting:
the potential use of this migratory movement to
increase the concentration of clam stocks is also
being investigated.

OYSTER BREEDING: WHERE CAN IT GO

William K. Hershberger

College of Fisheries
University of Washington
Seattle, Washington 98105

Based on the results that have been obtained
with other cultured organisms, particularly with
agriculturally-raised species, and the genetic
variability that has been found in oysters, it
should be possible to make significant strides in in-
creasing commercial production of this animal.
Before this possibility can be realized a concerted
effort must be made, and a systematic program
must be designed to initiate the process of
domestication. By definition this procedure in-
volves changing an organism for maximum per-
formance under conditions that are amenable to

efficient culture and harvest by man. Present
methods of commercial oyster culture employ on-
ly part of the domestication process in that,
generally a harvestable commodity is grown on
the basis on uncontrolled reproduction and semi-
controlled growing beds. These methods have
some significant implications concerning the in-
teraction of the genetic constitution of the oyster,
its environment, and its production potential.
These will be discussed with the use of standard
genetic models and programs suggested to further
enhance the production of oysters utilizing genetic
methodology and systematic breeding procedures.

A COMPARISON OF SURVIVAL, GROWTH,

AND YIELD OF PACIFIC OYSTERS

(CRASSOSTREA GIGAS) FROM SEED

OBTAINED FROM DIFFERENT SOURCES

Chris R. Jones

Washington State Department of Fisheries

Shellfish Laboratory

600 Pt. Whitney Rd.

Brinnon, Washington 98320

Experimental plantings of the Pacific oyster
(Crassostrea gigas) were conducted over a 3-year
period with the objective of establishing the
relative quality of various sources of oyster seed
and to develop methods to improve survival and
growth, especially during the first growing season.
The results were mixed, depending on the area
where grown and the methods used; but using
conventional cultural practices, it appears that
Japanese oyster seed will generally produce higher
yields compared to equivalent groups of hatchery-
produced or wild domestic seed. Japanese seed,
however, may suffer higher mortality during the
second year in some locations, indicating
resistance to mortality for domestic oysters. The
variables of seed size, seed density, hardening
methods, and off-bottom rearing were evaluated.
The initial size of the seed was found to be impor-
tant in some cases, but the problems of small size
were often more than offset by increased numbers
of spat per shell. Density-dependent mortality was
found to be linear through the range of densities
studied. Studies also showed that some alternative
methods of seed handling could improve the

PROCEEDINGS OF THE NATIONAL SHELLFISHERIES ASSOCIATION

ultimate yield. In particular, it was found that off-
bottom rearing for the first growing season more
than doubled the production by the end of the se-
cond season. The improvement was especially ap-
parent for the domestic seed. Some of the
"conventional wisdom" regarding the relative
quality of seed and the factors that determine
quality were found not to be generally true, and it
was apparent that each oyster grower must deter-
mine the factors that are most important for his
particular cultural situation.

PRELIMINARY REPORT ON MANILA CLAM

RESEEDING PROGRAM AT FIVE PUGET

SOUND BEACHES

Mark Miller1, Kenneth Chew1,

Charles D. Magoon2, Lynn Goodwin',

and Chris Jones2

'University of Washington

College of Fisheries
Seattle, Washington, 98105

'Washington Department of Natural Resources
Seattle Washington

iWashingto>i Department of Fisheries
Brinnon, Washington 98320

Receiving support from the Washington State
Sea Grant Program, the College of Fisheries along
with the Washington Departments of Fisheries and
Natural Resources have continued to investigate
the feasibility of planting hatchery spawned
Manila seed clams on Puget Sound beaches. Dur-
ing the past l1 2 years the major emphasis of the
project has been centered on determining the
causes for low recoveries of planted clams. Studies
carried out to gain a better understanding of the
problems involved have included providing pro-
tection for planted clams, planting clams in
modified substrate, determining clam predators
and testing for movement of planted clams. The
rearing of small seed clams in suspended sand- fill-
ed trays has also been conducted for the purpose
of obtaining advanced size clam seed for subse-
quent grow out on the beach. While the economics
of clam reseeding do not yet favor commercial ap-
plication, there seems to be a potential for this
which may be realized by further research.

SEED OYSTER PRODUCTION IN THE
SALTON SEA CALIFORNIA

Thomas L. Richards

Biological Sciences Department

California Polytechnic State University

San Luis Obispo, CA 93407

The Salton Sea is an inland body of salt water
located in the southern California counties of
Riverside and Imperial. The sea is approximately
70 kilometers long and 25 kilometers wide with
the water surface about 65 meters below sea level.
The salinity currently ranges from 33 0/00 to 37
0/00. The ionic content of Salton Sea water is not
the same as that found in oceanic water as the salt
comes from concentrated irrigation waste water.
Water temperatures, taken three meters below the
surface, range from winter low of 10 °C to a sum-
mer high of 37°C.

Attempts in the 1950's to establish oysters in the
Salton Sea were unsuccessful. Adult pacific oys-
ters, Crassostrea gigas, will live about 30 days in
Salton Sea water. It appears that even though the
Salton Sea water has abundant plankton the water
anesthetizes ciliary action and adult oysters are
unable to feed. Experiments utilizing Salton Sea
water to spawn oysters and culture larvae have
shown that all stages survive well and a commer-
cial spat fall can be obtained. Adequate spawning
and culture temperatures are present from May
through November each year. During this period
natually occurring phytoplankton counts range
from 0.5 to 3 million cells/liter.

Plans for a commercial oyster hatchery at the
Salton Sea have been reviewed and modified by
local, state, and federal regulatory agencies and all
necessary permits have been granted. Sufficient
financial support has been obtained to begin con-
struction, and it is planned that the facility will set
its first commercial oyster larvae during the late
spring of 1978.

PRELIMINARY STUDIES ON THE

DEVELOPMENT

OF A SYNTHESIZED DIET FOR JUVENILE

OYSTERS, CRASSOSTREA GIGAS

M.A. Toner

ABSTRACTS

The growth of juvenile Pacific oysters fed equal
amounts (based on ash free dry weights) of algae
(Pseudoisochrysis paradoxa), lysed algae, dried
oyster meat and encapsulated lysed algae was
monitored in three experiments. Dried oyster meat
and encapsulated lysed algae were also fed as sup-
plements to lysed algae at three levels: 25, 50 and
75 percent of the total ash free dry weight of the
diet. The growth of oysters fed lysed and whole
algal cells with and without the addition of
sodium sulfamethazine (Sulmet" ) was also com-
pared. Growth was measured as the difference in
ash free dry meat weight between treatments and
an initial sample frozen at the beginning of the ex-
periment.

In the first experiment, oysters fed algae alone
showed an increase in ash free dry weight that was
significantly greater than that of oysters fed dried
oyster meat alone and as a supplement to algae. In
the second experiment, oysters fed lysed algae
treated with or without Sulmet"1 showed a signi-
ficant decrease in ash free dry weight from the in-
itial sample. Oysters fed algae with and without
treatment with Sulmet" did not show a signifi-
cant increase in ash free dry weight. In the third
experiment, oysters fed starch encapsulated algae
and algae with and without supplementation with
encapsulated algae increased significantly in ash
free dry weight as compared to the initial sample.

Encapsulation appears to be a process which
could be used as a delivery system for feeding syn-
thesized diets to juvenile oysters.

CLAM RESOURCE MEASUREMENT FOR
ESTIMATION OF POLLUTION DAMAGE'

J. R. Vanderhorst and P. Wilkinson

Battelle Pacific Northwest Laboratories

Marine Research Laboratory

Sequim, Washington

Commonly used statistical procedures are
geared to assure we do not state in error that a
clam population has diminished in face of pollu-
tion while little attention has been given to the
corrollary need by private and public resource
managers to have assurance that a given reduction
in the clam resource will be detected. This paper
deals with the sampling requirements for detection

of change in population abundance of native little
neck clams (Protothaca staminea) on specific plots
in the north Puget Sound region. Example data are
presented which indicate that from 75 to 20,000
samples are required for detection of a 40 percent
to 5 percent change in abundance on sample plots
respectively. A pre-mapping procedure of sample
stratification which effectively reduced the sam-
pling requirement by one-half is also discussed.

This paper is based on work performed under U.S. Energy
Research and Development Administration Contract EY-
76-C-06-I830.

MUSSELING IN ON A NEW MARKET
Paul Waterstrat

University of Washington

College of Fisheries
Seattle, Washington QS105

The Mussel Project is currently involved in 3
areas of study: mussel set prediction; hatchery
development: and market investigation. Monitor-
ing of plankton and spat collectors has revealved
no significant mussel sets for spring and summer
1977 at study sites in Seabeck and Clam bays.
Plankton and water quality factors of tempera-
ture, salinity, and phytoplankton abundance will
continue to be monitored to provide a historical
baseline for the study sites.

The investigation of hatchery techniques for
rearing and setting mussel larvae has been under-
taken to provide information on the larval
development and settlement of local mussel stocks
and to develop a commercially feasible hatchery
system. The use of larval dimensions for iden-
tification of planktonic mussel larvae has been
strengthened by information gained from the
hatchery revealing that dimensions of larvae ob-
tained from Puget Sound stocks of Mytilus edulis
are comparable to those from New England
stocks.

Recent newspaper and magazine articles coupl-
ed with the publishing of a mussel cookbook have
increased public awareness of the delights to be
found in mussel dishes. A recent survey of 300
restaurants in Washington State reveals a signifi-
cant interest in mussels by restaurant owners and

PROCEEDINGS OF THE NATIONAL SHELLFISHER1ES ASSOCIATION

identifies poor consumer awareness, inadequate
supply and product quality to by the major im-
pediments for development of this market. Ex-
amination of mussels offered in retail markets
reveals that a poor product quality may be a great
detriment to the advancement of mussels as a
household food item.

PIGEON POINT SHELLFISH HATCHERY:
PAST, PRESENT AND FUTURE

Anthony Weaver

Pigeon Poi)it Shellfish Hatchery
921 Pigeon Point Road
Pescadero, CA $4060

The Pigeon Point facility was established in
1965 as a shellfish hatchery for the mass culture of
bivalve molluscs from egg to seed-sized juvenile
stages. Cultchless seed was developed at Pigeon
Point in 1968. Commercial success attained from
this development stimulated further expansion in
1Q70 in which a new building was built at Pigeon
Point and a cultch-setting facility was established
in Moss Landing.

The expansion brought about serious produc-
tion problems: larval mortality and inability to
grow sufficient algae to feed the spat. During this
period the Pacific Northwest seed market was pen-
etrated, but the inability to produce quality seed
quickly resulted in marketing failures.

The production failures became increasingly
severe and in 1°74 the operation went into a well-
financed research and development mode result-
ing in a successful pilot production program two
years later.

In January, 1976, a highly favorable technical
evaluation was made of the facility by an outside
group of mariculture scientists from such institu-
tions as Scripps, Woodshole, U.C., and O.C.U.
The group also included individuals from com-
mercial mariculture businesses.

On the basis of this evaluation, the facility was
redesigned and successfully put into commercial
operation in November, 1976.

Today, Pigeon Point Shellfish Hatchery is again
producing high quality cultchless oyster seed at a
yearly rate of about 30 million seed. A wide varie-
ty of species and sizes ranging from 2-3 mm and
25-40 mm (1 to 1.5 inches) are available.

While growers in Oregon have had a great deal
of success with the seed, the majority of the pro-
duct is planted in Europe and the Eastern United
States.

In the future, Pigeon Point intends to increase
production levels significantly and add new spe-
cies to the inventory list. We hope that more
growers in the Pacific Northwest will try our large
cultchless seed in their growouts. We would great-
ly appreciate suggestions of how we might be able
to fit into the oyster industry in this region.
Samples of our products are available at limited
cost.

VIBRIO ANGUILLARUM

AND LARVAL MORTALITY

IN A CALIFORNIA COASTAL SHELLFISH

HATCHERY

Ronald Thurber Zebal

Pigeon Poitit Shellfish Hatchery
Pescadero, Ca. $4060

The Pigeon Point Shellfish Hatchery has had a
mixed history of success in developing profitable
oyster spat production primarily because of larval
mass mortalities due to unknown causes. The
predominant bacterial species recently isolated
from mobid oyster veliger larvae produced under
hatchery conditions was identified as Vibrio
anguillarum. Infection of healthy larvae, and re-
peated recoveries of this bacterium from diseased
larvae confirmed this bacterial species to be one
cause of serious epizootics within the hatchery.
Routine screening for this organism and observa-
tion of larval behavior, coupled with appropriate
hatchery design and management techniques have
controlled this cause of larval mortality.

In the paper "Mercenaria culture using stone ag-
gregate for predator protection" by Castagna and
Kraeuter, Vol. 67, 1977, there is an error in the last
sentence before the results. The sentence states,
"Once the area had been stabilized, small clams
were broadcast over the aggregate at an average
density of approximately 31/sq. m." It should have
read 3100/sq. m.

MBl. WHOI LIBRARY

UH 1ABB $

Internet Archive Audio

Featured

Top

Images

Featured

Top

Software

Featured

Top

Books

Featured

Top

Video

Featured

Top

Mobile Apps

Browser Extensions

Archive-It Subscription

Save Page Now

Full text of "Proceedings of the National Shellfisheries Association"

See other formats