Natirw~l Wetlands Research Center

U, S. Fish and WildiifC Service

700 C’;jtirldome Uoukvard

Loiayetia , La. 70506

FWSIOBS-82/I 1.12

October 1983

TR EL-82-4

Species Profiles: Life Histories and

Environmental Requirements of Coastal Fishes

and Invertebrates (Mid-Atlantic)

BAY SCALLOP

QL

155

.S63

no.82-

11.12

Fish and Wildlife Service

U.S. Department of the Interior

Coastal Ecology Group

Waterways Experiment Station

U.S. Army Corps of Engineers

FWS/ORS-S2/11.12

TR EL-82-4

October 1983

Species Profiles: Life Histories and Environmental Requirements

of Coastal Fishes and Invertebrates (Mid-Atlantic)

BAY SCALLOP

Clemon W. Fay, Richard J. Neves, and Garland R. Pardue

Department of Fisheries and idi ldlife Sciences

Virginia Polytechnic Institute and State University

Blacksburg, VA 24061

Project Manager

Larry Shanks

Project Officer

Norman Benson

Yational Coastal Ecosystems Team

U.S. Fish and Wildlife Service

1010 Gause Boulevard

Slidell, LA 70458

This study was conducted

in cooperation with

Coastal Ecology Group

U.S. Army Corps of Engineers

Waterways Experiment Station

Performed far

National Coastal Ecosystems Team

Divisi:)n of Biological Services

Fish and Wildlife Service

U.S. Department of the Interiijr

Washington, I)(1 20240
CONVERSION FACTORS

Multiply

millimeters (mm)

centimeters (cm)

meters (m)

kilometers (km)

square meters (m') 10.76

square kilometers (km') 0.3861

hectares (ha) 2.471

liters (1)

cubic meters (m')

cubic meters

0.2642 gallons

35.31 cubic feet

0.0008110 acre-feet

milligrams (mg)

grams (gm)

kilograms (kg)

metric tons (mt)

metric tons (mt)

kilocalories (kcal)

Celsius degrees

inches 25.40 millimeters

inches 2.54 centimeters

feet (ft) 0.3048 meters

fathoms 1.829 meters

miles (mi) 1.609 kilometers

nautical miles (nmi) 1.852 kilometers

square feet (f-t')

acres

square miles (mi‘)

0.0929 square meters

0.4047 hectares

2.590 square kilometers

gallons (gal)

cubic feet (ft)

acre-feet

ounces (oz)

pounds (lb)

short tons (ton)

BTU

Fahrenheit degrees

Metric to U.S. Customary -__

BY

0.03937 inches

0.3937 inches

3.281 feet

0.6214 miles

0.00003527 ounces

0.03527 ounces

2.205 pounds

2205.0 pounds

1.102 short tons

3.968 BTU

1.8(C) + 32 Fahrenheit degrees *

U.S. Customary to Metric

3.785 liters

0.02831 cubic meters

1233.0 cubic meters

28.35 grams

0.4536 kilograms

0.9072 metric tons

0.2520 kilocalories

0.5556(F' - 32) Celsius degrees

To Obtain

square feet

square miles

acres
CONTENTS

Page

CONVERSION TABLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

PREFACE

ACKNOWLEDkMiNiS' : : : : : : : : : : : : : : : : : : : : : : : : : : : : :

iv

v

NOMENCLATURE/TAXONOMY/RANGE

MORPHOLOGY/IDENTIFICATION AI& : : : : : : : : : : : : : : : : : : : : : :

1

1

REASON FOR INCLUSION IN SERIES ...................... 3

LIFEHISTORY ............................... 3

Reproductive Physiology/Strategy .................... 3

Spawning ................................ 4

Eggs .................................. 4

Larvae ................................. 4

Juveniles ............................... 5

Adults ................................. 5

GROWTH CHARACTERISTICS .......................... 6

ECOLOGICAL ROLE ............................. 8

FoodHabits .............................. 8

Feeding Behavior ............................ 8

Predators ............................... 8

Competitors .............................. 9

Parasites ............................... 9

THEFISHERY ............................... 9

Commercial Fisheries .......................... 9

Recreational Fisheries ......................... 10

Population Dynamics

ENVIRONMENTAL REQUIREMEiT; : : : : : : : : : : : : : : : : : : : : : : : :

10

11

Temperature .............................. 11

Salinity ................................ 12

Temperature-Salinity Interaction .................... 13

Water Currents ............................ 13

Turbidity ............................... 13

Substrate ............................... 14

Oxygen Requirements .......................... 14

HeavyMetals .............................. 14

LITERATURE CITED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

. .

I II
PXEFACE

This species profile is one of a series on coastal aquatic organisms,

principally fish, of sport, commercial, or ecological importance. The orofiles

are designed to provide coastal managers, engineers, and biologists with a brief

comprehensive sketch of the biological characteristics and environmental requirements of the species and to describe how populations of the species inay be

expected to react to environmental changes caused by coastal development. Each

profile tias sections on taxonomy, life history, ecological role, environmental

requirements, and economic importance, if applicable. A three-ring binder is

used for this series so that new profiles can !)e added as they are prepared.

This project is jointly planned and financed by the U.S. Army Corps of Engineers

and the U.S. Fish and Wildlife Service.

Suggestions or questions regarding this report should be directed to:

Information Transfer Specialist

National Coastal Ecosystems Team

U.S. Fish and Wildlife Service

NASA-Slide11 Computer Complex

1010 Gause Boulevard

Slidell, LA 70458

or

U.S. Army Engineer Waterways Experiment Station

Attention: WESER

Post Office Box G31

Vicksburg, MS 39180

This series should be referenced as follows:

U.S. Fish and Wildlife Service. 1983. Species profiles: life histories and

environmental requirements of coastal fishes and invertebrates. U.S. Fish

and Wildlife Service, Division of Biological Services, FWS/OBS-82/11.

U.S. Army Corps of Engineers, TR EL-82-4.

This profile should be cited as follows:

Fay, C.W., R.J. Neves, and G.B. Pardue. 1983. Species profiles: life histories

and environmental requirements of coastal fishes and invertebrates (MidAtlantic) -- bay scallop. U.S. Fish and Wildlife Service, nivision of

Biological Services, FWS/OBS-82/11.12. lJ.S. Army Corps of Engineers,

TR EL-82-4. 17 pp.

iv
ACKNOWLEDGMENTS

We are grateful for the review by J. Michael Hickey, Massachusetts Division of

Marine Fisheries, Sandwich.

*L Figure 1. Bay scallop: left, external view of shell; right, internal view of shell.

BAY SCALLOP

NOMENCLATURE/TAXONOMY/RANGE

Scientific name.. . Argopecten irradians

Preferred common name.. . . . . Bay scallop (Figure 1)

Class.. . . . . . . . . . . . . . . . . . . . . . . . . Bivalvia

Order.. . . . . . . . . . . . . . . . . . . . . . .Anisomyaria

Family.. . . . . . . . . . . . . . . . . . . . .Pectinidae

Geographic range: North shore of

Cape Cod (42ON latitude, 70°W

longitude) south to Laguna

Madre, Texas (26’N, 97OW)

(Wailer 1969) (see Figure 2 for a

map of the distribution of the

bay seal lop in the mid-Atlantic

region). Three subspecies of

Argopecten irradians are generally recognized, intergrading in

distribution, with A. j. irradians

extending from Cape Cod to New

Jersey, A. j. concentricus from

New Jersey to the Chandeluer

Islands in the Gulf of Mexico,

and A. i. amplicostatus from Galveston, -Texas, to Laguna Madre,

Texas (Wailer 1969).

MORPHOLOGY/IDENTIFICATlON AIDS

Distinguishing among the queen

scallop (Chlamys opercularis), calico

scallop (Argopecten gibbus), and bay

scallop is difficult without specimens
- __\

I--.

, -.

PENN.

PHILADELPHIA

MD.

c

BALTIMORE i

-TV0

KILOMETERS

1

%z#

d

- -

Offdfs~lit of

F A

..,

.,. ST%;;’ Important Commercial

~%d Fishing Ground

$pGQj- \‘F APE HATTERAS

Figure 2. Mid-Atlantic distribution of the bay scallop.

2
of all three for comparison. The most

diagnostic feature for separation is

the difference in relative convexity of

left and right valves among species.

The queen scallop is distinctly left

convex ; that is, the left valve is more

rounded than the right. The calico

scallop valves are slightly left convex

or equiconvex. In contrast, the bay

scallop is distinctly right convex; that

is, the right valve is more rounded

than the left (Broom 1976). A list of

other qualitative characters, useful

when all three species are in hand,

and a dichotomous key for species of

the genus Argopecten are presented

in Broom (1976).

Bay scallop shells are symmetric

or nearly so, with a distinct notch on

the anterior edge of the hinge.

Valves possess 13 to 22 radial ribs

(less than 18 on A. i. amplicostatus

and more than 14 %n A. i. irradians

and A. i. concentricus) (Broom 1976).

Normal adult size ranges from 55 to 90

mm (2.2 to 3.5 inches) in diameter.

Color of the left (top) valve varies

considerably, but generally is dark

grey, black, or brown, and sometimes

with red, orange, or yellow hues;

mottling or concentric banding also

occurs . Right valves vary from yellow or white to nearly as dark as left

valves; additional markings usually

are absent, but if present, they are

similar to those on the left valve

(Wailer 1969).

REASON FOR INCLUSION IN SERIES

Bay scallops have been harvested

since colon ial times, and in recent

years (for example, 1976), accounted

for up to 946 metric tons (mt) (1,041

tons) of scallop meats (Peters 1978).

Of the three commercially exploited

scallops of the Atlantic coast, the bay

scallop ranks well behind the sea

scallop (Placopecten magellanicus) and

about equal to the calico scallop in

magnitude of catch ( Peters 1978). I n

terms of exvessel price (at the

ports), bay scallops are of higher

value to fishermen than are sea scallops.

In addition to their economic

importance, bay scallops are included

in the series because of their vulnerability, the difficulty in managing

them, and their importance in the food

web. Their distribution is entirely

estuarine or near-coastal (less than

4.8 km or 3 mi offshore, and within

State territorial waters), making them

vulnerable to recreational and industrial development along the shore.

Also, bay scallops are short-lived

(generally less than 26 months); consequently, exploitable stocks vary considerably from year to year, making

management and yield prediction difficult (Peters 1978). Finally, the species is an important link in the estuarine community food web, funneling

energy from planktonic and benthic

organisms to aquatic and terrestrial

predators (Belding 1910).

LIFE HISTORY

Reproductive Physiology/Strategy

Bay scallops are hermaphroditic

and generally protandrous (releasing

male gametes before female gametes)

(Loosanoff and Davis 1963; Peters

1978). A single individual may

release both types of gametes in a

single spawning period (Peters 1978);

but because of protandry, self-fertilization in nature is probably rare

(Belding 1910; Gutsell 1930). Bay

seal lops mature and spawn for the

first time at approximately 1 year of

age. Although size at age 1 varies

because of differences in growth rates

among populations, maturity is a

function of age, not size (Gutsell

1930; Marshall 1960; Broom 1976).

Since the average longevity is only 12

to 16 months, and maximum longevity

about 26 months (Belding 1910), few
individuals spawn more than once

(Peters 1978).

Spawning

In the mid-Atlantic region, bay

scallops spawn from mid-April through

early September (Chanley and

Andrews 1971). Specific spawning

times, however, vary considerably

across the species range. In Massachusetts (Belding 1910), Connecticut

(Cooper and Marshall 1963), Rhode

Island (Risser 1901), and Long Island

Sound (Hickey 1978), most spawning

occurs during June and July, as

water temperatures increase. In contrast, populations in North Carolina

(Gutsell 1930; Sastry 1966) and Florida (Sastry 1963; Barber and Blake

1983) spawn between August and

December, as water temperatures

decrease. This apparent latitudinal

difference in spawning time may represent different physiological adaptations to environmental conditions

among the three recognized subspecies

of bay scallops (Sastry 1970a).

Gametogenesis and spawning time

of bay seal lops are correlated with

water temperature and food supply

(Turner and Hanks 1960; Sastry 1963,

1966, 1968, 1970a, 1970b; Sastry and

Blake 1971; Hickey 1978). A water

temperature of at least 15OC (59OF)

was necessary for initiation of gametogenesis in overwintering bay scallops,

while at least 20°C (68OF) and adequate food supply were necessary for

gametogenesis to reach the “germinal

vesicle dissolution” stage (Sastry

1968). Temperatures above 20°C and

adequate food were necessary for

gametes from winter-collected scallops

to reach a fertilizable stage. For

spring-collected scallops, maturation

and spawning occurred with or without food for scallops held at 20°C,

25OC (77’F), and 30°C (86OF), while

those held at IOOC (5OOF) and 15OC

did not mature and spawn (Sastry

1966), Sastry (1970a). stated that

variation in reproductive physiology in

geographically separated bay scallop

populations (Woods Hole, Massachusetts, compared to Beaufort, North

Carolina) is probably an adaptive

response to differences in water temperatu re regime and timing of 4

maximum available food supply.

Eggs

Unfertilized bay scallop e99s

average 60 millimicrons (mp)’ in diameter (Broom 1976), and range from 55

to 65 mu (Loosanoff and Davis

1963). Eggs are often asymmetrical

prior to release into water (Loosanoff

and Davis 1963), but rapidly become

spherical or nearly so after release

(Belding 1910). Yolk granules are

numerous and small. Fertilization

occurs in the water column or on the

bottom, and fertilized eggs are demersal (Belding 1910; Broom 1976). Egg

development accelerates as water temperatu re increases ( Broom 1976);

however, a critical thermal minimum

between 15’ and 20°C (59” and

68OF) was reported for successful

early cleavages to occur (Sastry

1966). Gastrulation occurred in 9 hr

at 24OC (75OF) (Sastry 1965); subse- 4

quent stages of embryogenesis are

presented in Belding (1910) and Gutsell (1930).

Larvae

At 24OC to 25OC (75OF to 77OF),

trochophore larvae first appeared from

swimming gastrulae (Belding -1910)

after 24 hr, and all surviving eggs

had developed into trochophore larvae

by 48 hr (Gutsell 1930; Sastry 1965).

Gradual transformation to veliger larvae (first appearance of a shell)

began shortly after. reaching the

trochophore stage and was completed

by most larvae in 48 hours (Gutsell 1930;

Sastry 1965). Average size of veliger

larvae reared at 24OC was 101 mu

(Sastry 1965). The veliger larvae

began feeding activity by using their

ciliated velum. By the third day of

the veliger stage, average shell size

l Imp = 1 nanometer or 10e9m.
was 122 mv, and the straight-hinged

veliger shell began to develop curved

umbones characteristic of the pediveliger stage. The veliger stage lasted

about 10 days; . .

& was fully dezlloi”,f t’?~edt~~el~~~~

stage), and metamorphosis to the

juvenile stage occurred. Average

shell length of juveniles at settlement

was 190 mu, gills

the velum was

(Sastry 1965).

had developed, and

completely absorbed

Total time between egg fertilization and settlement is about 14 days

(Loosanoff and Davis 1963; Sastry

1965), but ranges from 10 to 19 days

(Castagna and Duggan 1971), depending not only on water temperature but

also food supply. Unfed larvae will

not metamorphose ( 6 room 1976).

Detailed observations on larval development of bay scallops are given in

Belding (1910) and Gutsell (1930).

Juveniles

Characteristics of the juvenile

stage are settlement and appearance of

the dissonconch shell, a thin, fragile,

postveliger structure, completely

separated from the thicker, veliger

shell (Sastry 1965). Upon settlement

to a suitable substrate, the juvenile

scallop attaches by a fine thread

called the byssus, which is secreted

by a special gland in the foot (Belding 1910; Broom 1976). If the attachment surface is suspended off the

bottom (e.g., a blade of seagrass),

the juvenile will remain attached until

it reaches 20 to 30 mm (0.8 to 1.2

inches) in length, at which time it

drops to the bottom (Castagna 1975).

Very young scallops (< 10 mm or 0.4

inches) apparently cannot tolerate

highly silted substrates (Castagna

1975); thus, attaching to epibenthic

surfaces until reaching 20 to 30 mm

and then dropping to the bottom

probably improves their survival rate

(Castagna 1975).

Juvenile bay scallops use a

variety of substrates as settlement/attachment locations, including stones,

seaweeds ( Ingersoll 1886), oyster

shells, rope, and filamentous algae

(Marshall 1960). Beds of eelgrass

(Zostera marina) and other seagrasses

are apparently preferred as settlement

locations (Thayer and Stuart 19741,

though scallops are able to settle and

survive in areas lacking seagrasses

(Marshall 1947, 1960). Kirby-Smith

(1972) found that young bay scallops

grew faster in slow currents compared

to fast currents; and since seagrass

beds tend to slow normal water currents (Castagna 1975), availability of

these plants may enhance growth

rates.

Upon settlement, juveniles climb

and crawl using the foot, byssal

threads, and tentacles until the swimming powers of the adult develop.

The foot is also used for turning

over, should the young scallop accidently land on its left valve (characteristically, all bay scallops rest and

feed on their right valve) (Belding

1910; Gutsell 1930).

Juvenile bay scallops tend to

vary more in coloration than adults,

and range from nearly pure white to

dark grey or brown, with some predominantly red individuals present.

Lightly colored young scallops darken

as they age, while darker juveniles

change little in color (Belding 1910).

Adults

The adult stage is characterized

by the radial ridges and furrows often

observed on scallop shells. Once the

ridges appear, they do not increase in

number as the scallop grows (Belding

1910). Another distinguishing characteristic of adults is a concentric

ridge on the shell (vs. radial ridges).

It is caused by slow growth during

the first winter of life, and is analogous to an annulus on a fish scale.

This shell character is often used by

5
law enforcement personnel to determine whether illegal (subadult) scallops have been commercially harvested

( Peters 1978).

Even though adult scallops retain

the ability to attach by byssal threads

(Castagna 1975; Peters 1978), they

are seldom found attached in nature

(Castagna 1975) . Adult scallops prefer quiet waters, protected from high

winds, storms, and tides (Belding

1910). Preferred depths range from

0.3 to 10 m (1 to 33 it), though

occurrence to 18 m (59 ft) has been

reported (Belding 1910; Broom 1976).

Scallops are often most abundant on

tidal flats with only 0.3 to 0.6 m (1 to

2 ft) of water at low tide.

Adult bay scallops are effective

swimmers at all sizes (Castagna 1975).

The mechanism for swimming is pulsed

expulsion of water from the mantle

cavity (called “clapping” in much of

the literature). Alternation of

expelled water out the anterior and

posterior gapes of the shell results in

a swimming motion that appears zigzag. Alternate expulsion is apparently

voluntary, as bay scallops can also

move sideways by using only one end

of the shell for water release (Belding

1910; Gutsell 1930). Voluntary movement of bay scallops is used to escape

unfavorable environmental conditions

or predators (Belding 1910; Gutsell

1930; Moore and Marshall 1967).

Using tagged scallops from the Niantic

River Estuary, Connecticut, Moore

and Marshall (1967) found that summer

movements of bay scallops were 0.8 m

(2.6 ft) or less from release points

over the maximum observation period

of 6 days. Successive movements by

individuals were not directional, but

pooled movements of released groups

were slightly but significantly directional. Directionality, however, may

have resulted from tidal influence on

otherwise random individual movements

(Moore and Marshall 1967). Belding

(1910) also noted that much of the

scallop movement observed was

directional only under the influence of

tidal currents. Though the possibility

of long-range migrations by bay scallops was noted in Belding (1910), no

such evidence for extensive migrations

has been presented (Baird 1966;

Moore and Marshall 1967).

The average life span of bay

scallops ranges from 12 to 24 months

in waters south of Maryland (Gutsell

1930; Sastry 1961; Castagna 1975),

and from 20 to 26 months in waters

north of Maryland (Belding 1910; Marshall 1960; Russel 1971; Robert 1978).

Maximum reported life span was 26

months (Belding 1910) to 30 months

(Robert 1978) for populations north of

Connecticut.

GROWTH CHARACTER ISTICS

Growth rates of t>ay scallops seem

to depend on water temperature, current velocity, food availability, and

possibly sea I lop density. Growth

rates in shell diameter reported in

early literature varied from 3.8 to 8 -

mm (0.1 to 0.3 inches) per month,

with most of this growth occurring

during the 4 or 5 warmest months of

the year (Risser 1901; Belding 1910;

Gutsell 1928). Belding (1910) found

that growth of Massachusetts bay

scallops ranged from 3.8 to 4.5 mm

(0.1 to 0.2 inches) per month over 3

years of study. Growth rate was

highest in May, August, September,

and October, and only about half as

fast in June and July, when these

populations spawned. Gutsell (1928)

reported that North Carolina scallops

may begin to grow as early as February, even though water temperatures

may be as low as 3OC (37OF). Growth

ceased after October, even though

water temperatures were still above

20°C (68OF). In North Carolina,

spawning occurs in September and

October, and this cessation of growth

occurred immediately thereafter.
Water currents were demonstrated

to affect growth of scallops. KirbySmith (19.72) reported that scallops

held at 27OC (81OF) over 21 days

showed no growth at a current veiocity of 12.4 cm/s (0.4 ft/s); those exposed to 3 to 4 cm/s (0.10 to 0.13 ft/s)

grew an average of 0.5mm (0.02 inch);

exposure to 0.75 and 0.21 cm/s (0.02

and 0.007 ft/s> produced the highest

growth rate of 4 mm (0.16 inches)

(5.7 mm or 0.22 inches/month). Scallop

growth in standing water was not

investigated. Kirby-Smith (1972)

demonstrated that phytoplan kton

removal by scallops was most efficient

at the slower current speeds, and this

may account for the observed growth

patterns.

Kirby-Smith and Barber (1974)

found that the optimum combination of

temperature and food particle density

for growth was 1.2 ug/l of chlorophyll

a_ at 22OC (72OF). Growth was lower

at higher temperatures (e.g., 28OC or

82OF), even with higher food particle

density (2.4 pg/l chlorophyll a). The

relationship between growth and food

particle density was:

V = Vm (S - a)/(C - a) + (S - a)

where V = growth rate, Vm = maximum

growth rate (saturation), S = optimal

food particle concentration, C = value

of S at Vm/2, and a = value of S

when V = 0. Using this equation,

there is a different value of S for

each temperature (Kirby-Smith and

Barber 1974).

Duggan (1973) found that bay

scallops from Virginia waters held in

cages at the surface, 1 m (3.3 ft)

below the surface, 2 m (6.6 ft) above

the bottom, and 1 m above the bottom, showed no significant difference

in growth rate over 5 months.

Observed growth ranged from 41.5 to

45 mm (1.6 to 1.8 inches) over the 5

months. Effects of scallop density on

growth were also investigated. up to

a size of 27 to 28 mm (1.06 to 1 .lO

inches), growth was not significantly

different at scallop densities of 1075,

806, 537, and 269/m’ (100, 75, 50,

and 25/ft2, respectively) ; above this

size, growth decreased with increasing

density. At termination of the experiment (4 months), average size ranged

from 40 mm (1 .6 inches) at the highest density to 49 mm (1.9 inches) at

the lowest density (Duggan 1973).

Growth rates over 3 mcnths,

mean size at age, and mean weight at

age were consistently lower for North

Carolina bay scallops experimentally

infected with female pea crabs (Pinnotheres maculatus, an internal, commensal parasite of bay scallops), compa red to uninfected scallops

(Kruczynski 1972). Evidence indicated that parasitism by the pea crab,

though not directly fatal to the scallop, affected the ability of bay scallops to grow (Sastry 1961; Kruczynski

1972).

Cooper and Marshall (1963)

investigated the condition of bay scallops in relation to the environment in

four separate populations of the Niantic River, Connecticut. Environments

of the four populations were generally

similar except for tidal current; two

populations were in relatively currentfree areas, and two were in areas

with strong tidal currents. The formula for calculating bay scallop condition was:

K = V/LN

where K = condition, V = muscle volume, L = shell height, and N = the

slope of the regression of log(V) to

log(L). Condition increased with age,

except during and after spawning in

June and July, when condition

decreased in all four populations.

Condition was highest in populations

located in slow-current environments,

even though the highest densities of

scallops occurred at one of the two

strong-current environments. The

relationship between condition and age

7
for all four populations combined,

applicable to scallops of age 7 to 20

months, was (Cooper and Marshall

1963) :

log(K) = 0.06197(t) - 0.06203

where t = time in months.

ECOLOGICAL ROLE

Food Habits

Investigations by Davis and Marshall (1961) indicated that the primary

food of bay scallops was benthic

diatoms. Characteristically, planktonic

forms of algae were present in very

low densities in stomachs compared to

benthic forms. Also, benthic-oriented

bacteria and miscellaneous or unidentifiable detritus were found in bay

scallop stomachs, further indicating

the importance of benthically derived

food sources (Davis and Marshall

1961).

I l-l the laboratory, larval bay

scallops were successfully reared on

suspensions of either green algae

(Chlorella spp. ), or a combination of

naked flagellates (Isochrysis galbana

and Monochrysis lutheri) (Loosanoff

and Davis 1963; Sastry 1965).

Growth was better on the flagellate

diet (Loosanoff and Davis 1963).

Both larval and adult bay scallops

were reared and maintained successfully on either flagellates (M. lutheri

and Dunaliella tertiolecta) or diatoms

(Phaeodactylum t ricornutum) (Castagna and Duggan 1971).

Feeding Behavior

Bay scallops are filter-feeders,

pumping water through the mantle

cavity and straining food particles on

the gill cilia (Broom 1976). Observations by Kirby-Smith (1970) indicated

that pumping was continuous; however, the investigator suggested that

rate and duration of feeding may be

modified according to food particle

densities. Filtration rate appeared to

be related to body size; assuming that

the r lationship can be described by F

=

&

KW , where F = filtration rate, W = _

body weight and K and b are constants, Kirby-Smith (1970) obtained a

value of -0.58 for b. Filtration rates

for scallop size classes of 38 to 44 mm

(1.49 to 1.73 inches), 47 to 48 mm

(1.85 to 1.89 inches), 54 to 56 mm

(2.13 to 2.20 inches), and 64 to 65

mm (2.52 to 2.56 inches) were

reported at 0.99, 0.93, 0.79, and 0.71

I/h r/g wet weight, respectively

(Chipman and Hopkins 1954).

Normal feeding position of adults

is resting on the bottom on the right

valve, with a shell gape of approximately 20’ (Belding 1910). Water

movement through the body is from

anterior to posterior. When the scallop occasionally lands on its left

valve, it quickly flips over using its

foot and water expulsion (Belding

1910). In coarse sand substrates,

shallow burrowing may be used during

feeding, with the right valve buried

in the sand and the left valve exposed

to the water (Belding ?910).

Predators

In shallow water areas, where

bay scallops are often abundant, the

most important predators are probably

the green crab (Carcinides maenes)

(Marshall 1960) and the blue crab

(Callinectes sapidus) (Castagna 1975).

In water deeper than 2 m (6.6 ft),

principal predators are the asteroid

starfish Asterias spp. and Marthaste-

_rias SPP. (Gutsell 1930; Marshall

1960). Starfish attack the scallop by

attaching tube feet to both valves and

pulling in opposite directions until the

adductor muscles of the scallop fatigue

(Belding 1910). Another predator is

the oyster drill (Urosalpinx cinerea)

(Marshall 1960). Gutsell (1930), however, noted that the total mortality

from oyster drill predation was
insignificantly low, because of the

long time period the drill needs to

bore and consume its prey (at least 8

days total, Belding 1910), and the

ability of bay scallops to respond

quickly to tactile stimuli and escape

predators (Belding 1910; Gutsell

1930). Lastlv, the herring SUII

(Larus arqentat.us) (Gutsell 1930) and

probably other gulls and terns (Family

Laridae) are important predators of

bay scallops. Because of the shallow

water habitats frequented by bay

scallops, predation by sight-feeding

birds is effective. A commonly

observed feeding behavior of gulls is

to grab the scallop with their bill, fly

up over the beaches or roads, and drop

the scallop to break the shell (Gutsell

1930).

Competitors

No evidence is available on interspecific competition involving bay

scallops. There is some evidence of

intraspecific competition. Density

studies by Duggan (1973) indicated

that very high scallop densities (on

the order of 1075/m’ or lOO/ft’)

ti decreased growth and increased mortality compared to lower densities

(269/m’ or 25/ft2). Even the lowest

densities tested by Duggan (1973),

however, were considerably higher

than densities in natural populations

studied by Cooper and Marshall (1963)

and Thayer and Stuart (1974).

Parasites

The pea crab is an internal commensal parasite of bay scallops (Cheng

1967), and the gastropod Odostomia

seminuda has been reported as an

ectoparasite (Cheng 1967). Kruczynski (1972) reported that bay scallops

infected with pea crabs grew slower

and were consistently lower in mean

dry weight than uninfected scallops.

Incidence of infection with pea crabs

ranged from 48 in fall to 10% in summer in Bogue Sound, North Carolina.

The percentage of infected bay

scallops in Alligator Harbor, Florida,

ranged from 13% to 36% seasonally

(Sastry and Menzel 1962).

THE FISHERY

Commercial Fisheries

All bay scallop landings come

from areas within 4.8 km (3 mi) of the

coast, and most from inside the contiguous coastline (inland waters).

Published information about the distribution of landings along mid-Atlantic

States is not available, but Gusey

(1976, 1981) indicated that the most

important commercial fishing grounds

for bay scallops are the south shore

of Cape Cod, Long Island Sound,

Sandy Hook Bay (New Jersey), Great

Egg Harbor (New Jersey), Delaware

Bay, nearshore Delmarva Peninsula,

and all of Chesapeake Bay proper (see

also Figure 2).

Modern bay scallop fisheries use

small dredges, approximately 1 m (3

ft) wide, towed by small powerboats.

In shallow water areas, dip nets,

rakes, and hand-gathering are also

used (Peters 1978). Most harvesting

occurs in water less than 6 m (20 ft)

deep (Gutsell 1928, 1930; Marshall

1960). In most mid-Atlantic States,

the scallop fishing seasons are from

autumn through spring, usually October to April (Marshall 1960; Broom

1976).

Although the current 5-year

average of U. S. bay scallop landings

(1977-81) was 585 mt (643.5 tons),

landings have fallen steadily from 946

mt (1041 tons) in 1976 to 437 mt (481

tons) and 302 mt (332 tons) in 1980

and 1981, respectively. The dollar

values of the 1980 and 1981 landings

were $3,894,000 and $2,427,000,

respectively (National Marine Fisheries

Service 1978-1982).

9
Since bay scalloDs are

short-lived, landings respond quickly

to fluctuations in year-class strength.

Thayer and Stuart (1974) provided

evidence that the dredging method

used for harvesting scallops may

account for the decline of landings in

dredged areas. In areas where beds

of eelgrass or other seagrasses are

fundamental to the presence and survival of bay seal lop populations

(including nearly all exploited scallop

beds), dredging alters the eelgrass

and therefore may cause poor harvests

for several years after an initial scallop dredging. Eelgrass requires several years to recover to a density

suitable for use by young bay scallops. Thayer and Stuart (1974)

reported that hand-raking,. another

method of bay scallop harvest, did not

significantly alter eelgrass beds, and

although less efficient in catch per

unit effort, appeared to be a better

method for sustaining a long-term

yield of bay scallops from a given eelgrass bed.

Recreational Fisheries

The recreational bay scallop catch

from Massachusetts waters increased

steadily (except for 1977) from 5,660

bushels in 1975 to 21,647 bushels in

1980, then dropped off to only 8,762

bushels in 1981. The recreational

catch represents from 4.5% to 14.88 of

the total Massachusetts bay scallop

landings in any one year (the remainder taken commercially). Inshore

waters around the Massachusetts

towns of Brewster, Chatham, Falmouth, Nantucket, Dennis, and

Bourne accounted for the majority of

recreational landings each year (Commonwealth of Massachusetts Shellfisheries Statistics 1982’).

Population Dynamics

Age and size composition. Only

two age classes are usually represented in bay scallop populations

2 No published document; tabulated

catch data received from Frank Germano, Assistant Marine Fisheries Biol0g.ai*t for the Commonwealth of

Massachusetts.

because of iheir short life span.

Annua! catches therefore vary almost

directly with fluctuation in year-class

strength. Age at first capture is

approximately 1 year, and few

2-year-old scallops appear in scallop _

landings or natural populations (Broom

1976). In North Carolina populations,

two size modes occurred: at 0 to 15

mm (0 to 0.6 inches) and 35 to 49 mm

(1.4 to 1.9 inches) in March, at 0 to

5 mm (0 to 0.2 inches) and 55 to 70

mm (2.2 to 2.8 inches) in August,

and at 0 to 10 mm (0 to 0.4 inches)

and 65 to 75 mm (2.6 to 2.9 inches)

in November (Gutsell 1930). Large

numbers of scallops in the 0- to 5-mm

class appeared in August, and

increased steadily through November,

reflecting the August-October spawning season in North Carolina (Gutsell

1930; Broom 1976).

Density. Cooper and Marshall

(1963) found that densities of bay

scallops at four locations In the Niantic River, Connecticut, ranged from 3

to 5/m2 (0.3 to 0.5/ft2) in a slackwater environment, 11 to 25/m2 (1 .O to

2.3/ft2) in intermediate currents, to

65 to 75/m’ (6.0 to 7,0/ft”) in high 4

currents . For North Carolina bay

scallop populations, Thayer and Stuart

(1974) reported densities of 24.8,/m”

(2.3/ft2) and 19.5/m2 (1.8/ft’) in two

separate areas . Densities in natural

populations observed by cooper and

Marshall (1963) and Thayer and Stuart

(1974) were much lower than those

tested by Duggan (1973) for effects of

density on scallop growth. Therefore,

densities in most natural populations

are probably not high enough to cause

a decrease in growth rate.

In the populations studied by

Thayer and Stuart (1974), average

scallop density was reduced from

24.8/m2 (2.3/ft2) to 16.7/m2 (1 .6/ft2)

in one population by 6 man-hours of

hand raking. In a second population,

average density dropped from 19.5/m2

(1 .8/ft2) to 3.0/m2 (0.3/ft2) after 6

man-hours of raking and 2 man-hours

of dredging. These data indicated

that scallop harvest by dredging,
even under light fishing prczssure,

quickly depleted exploitable scallops in

an area (Thayer and Stuart 1974).

Mortality. Average monthly mortality of lo-mm (0.4-inch) bay scallops

maintained in trays (but otherwise

under natural conditions) from November 1969 to November 1970 was 7% or

lower, except during the August-toSeptember interval, when mortality

was 13% (Castagna and Duggan 1971).

In depth experiments with bay scallops I Duggan (1973) found that total

mortality over 4 months was 4% at 2 m

(6.6 ft) off the bottom, 8% at 1 m

(3.3 ft) below the surface, 16.5% at

the surface, and 29.0% at 1 m above

the bottom. The higher mortality at 1

m from the bottom was probably

caused by heavy siltation of holding

cages at that depth; many times scallops were completely buried in silt.

In density tests, total mortality was

similar for scallops up to 27 to 28 mm

(1.06 to 1.10 inches), regardless of

density; above that size, mortality

increased with increasing density.

Total mortality over 4 months ranged

from 3.2% at the lowest test density of

269/m2 (25/ft2) to 35.0% at the highest test density of 1075/m’ (100/ft2)

(Duggan 1973).

Aquacultural potential. Studies

by Kirby-Smith (1972), Kirby-Smith

and Barber (1974), Castagna -(1975),

and Epifanio (1976) provided information on aquacultural potential and

requirements for bay scallops. These

studies identified the control of water

temperature (particularly in relation to

gonad development and spawning),

salinity, food supply, water currents,

scallop density, and predators as most

important for successful rearing of

bay scallops. Castagna (1975) provided the most comprehensive review

in terms of aquacultural potential.

Introduction potential. Robert

(1978) discussed the potential for

introduction of bay scallops into Maritime waters north of the Gulf of St.

Lawrence. Several limiting factors to

successful introduction were noted :

(1) very cold (<2OC or <36OF), icecovered waters for a minimum of 4

months; (2) high number and intensity of spring freshets, frequently

reducing salinity below the minimum

requirement of 14 ppt; (3) Iim.ited

food supply at the appropriate time

for settling juveniles; and (4) eelgrass beds occurring on silt substrates, and perhaps less suitable

than those on sand and mud substrates further south. Other factors

of importance to bay scallop survival

and growth, such as appropriate

depths, water currents, and protection from storms, were considered to

be at least marginally acceptable in

Maritime waters. Robert (1978)

recommended that if scallops were

introduced, seed stock should be

gathered from waters nearest in environmental conditions to Maritime

waters.

ENVIRONMENTAL REQUIREMENTS

Temperature

Castagna (1975) reported that

survival and development of eggs were

best at water temperatures above 20°C

(68OF). Optimum temperatures for

development appeared to be 26’ to

28OC (79’ to 82OF). Belding (1910)

stated that Massachusetts bay scallops

need a temperature over 7.2OC (45OF)

for growth, and growth rate was

closely tied to temperature and food

SUPPlY. Marshall (1960) found that

adult bay scallops tolerated exposure

to air temperatures as low as -6.6OC

(2OOF) for 2 hr. Below this temperature, tolerance time decreased.

Probably the most significant

information on the effects of temperature on bay scallops is that contained

in a series of studies by Sastry

(1963, 1966, 1968, 1970a, 1970b), and

b y Sastry and Blake (1971) on

11
relationships between temperature,

food, gonad development, and spawning. Overwintering scallops in a

“resting reproductive state” could not

survive d i rect exposure to 25OC

(77OF) or 30°C (86OF). They survived at 25OC if an acclimation period

of 30 days at 15OC (59OF) or 20°C

(68OF) and adequate food were provided. Gametogenesis was stimulated

in all overwintering scallops held at

15OC and 20°C, with or without food;

but the most advanced stage of gametogenesis (dissolution of germinal vesicle) was achieved only by scallops

held at 20°C with adequate food.

After dissolution of the germinal vesicle, temperatures greater than 20°C

were necessary for gametes to attain a

fertilizable stage (Sastry 1966, 1968).

Scallops collected in spring and early

summer, in a “reproductive development” stage, matured and spawned

rapidly when held in the laboratory at

20°C, 25OC, or 30°C, even without

food. Spring-collected scallops held

at 10°C (5OOF) and 15OC (59OF) did

not mature and spawn. Also, tolerance of changes in water temperature

was lowest for ripe scallops, and much

higher for “reproductive development”

stage individuals (Sastry 1966). Sastry (1970b) and Sastry and Blake

(1971) concluded that both food and

temperature were important factors

determining initiation and overall rate

of gonadal development, readiness to

spawn, and spawning time, and therefore may account for geographic differences in spawning activities

observed over the species range (Sastry 1970a).

Salinity

Because of the estuarine habitat,

bay scallops are frequently exposed to

changes in salinity, especially when

salinity is reduced from freshwater

runoffs (Duggan 1975). Castagna

(1975) reported that the minimum

salinity required for eggs to develop

to the straight-hinged veliger larval

stage was 22.5 ppt. In general, the

minimum sdinitv requirement determining overall distribution patterns of

settling juveniles and adults is about

14 ppt (Belding 1910; Gutsell 1930;

Sastry 1961; Castagna and Chanley

1973). Bay scallops have occasionally

been found at salinities as low as 10

ppt (Gutsell 1930), but whether this

was the prevailing salinity at the collection site was not indicated. Vernberg et al. (1963) reported that exposure to 12-15 ppt caused gill cilia to

cease beating.

Transfer of scallops from 28 ppt

to 21 ppt, 14 ppt, and 7 ppt salinity

was conducted by Sastry (1961). No

observable change in behavior was

noted for scallops moved to 21 ppt

and 14 ppt; however, transfer to 7

ppt induced scallops to close their

valves tightly for an extended period.

After an apparent period of acclimation, the valves slowly opened, but

tentacles were not extended and water

was not actively circulated through

the scallop body. Sastry (1961) did

not report whether any transferred

scallops attempted movement. Test

specimens were able to tolerate 2 hr

of exposure to 7 PPt, and after

transfer back to 28 ppt, resumed normal water filtration. Sastry (1961)

also reported that direct transfers

from 28 ppt to distilled water for up

to 2 hr did not affect scallop survival.

Duggan (1975) investigated the

effects of gradual reductions in salinity on bay scallops, since under natural conditions, reductions are more

gradual than in the situations tested

by Sastry (1961). Salinity in test

aquaria was reduced from 26 ppt to 6

ppt over 4 hr. Behavior of control

and experimental specimens was

observed and classified into one of

four activity modes, ranging from

“normal activity” to “no activity.” At

loo to 15OC (50° to 59OF), all

experimental animals showed “reduced

activity” as salinity reached 22 ppt,

and “no activity” when 16 ppt was

12
reached. At 20’ to 25OC (68O to

77OF), ” red u ted activity” occu r red

between 22 ppt and 18 ppt, and all

test animals showed “no activity” when

L

salinity reached 12 to 13 ppt. Initial

response of the test animals to introduction of freshwater was a higher

than normal clapping rate (the swimming movement of scallops). One-half

of the scallops of one test group was

transferred at the end of the 4-hr

experiment directly into 26 ppt, while

the other half was transferred after

15.5 total hr at 6 ppt. Both groups

survived and resumed normal filtration

activity upon transfer to 26 ppt

(Duggan 1975). This evidence suggested that short periods of exposure

to low salinities, such as from heavy

runoff, probably does not affect survival of bay scallops.

Temperature-Salinity Interaction

Bay scallop embryos require a

narrow range of temperature-salinity

combinations for proper development.

The optimum combination for normal

development was reported at 20°C

(68OF) or 25’C (77OF) (test temperatures at 5OC increments) and 25 ppt

salinity. Salinities above or below 25

PPt significantly affected normal

embryonic development. No embryos

developed normally at 10 ppt or 15

ppt salinity, or at water temperatures

of 10°C (5OOF) or 35OC (95OF) (Tettelbach and Rhodes 1981).

Bay scallop larvae could not tolerate lo-ppt salinity or 35OC; at least

some larvae survived at all other test

temperatures and salinities. Maximum

larval survival occurred at 20°C and

25 ppt salinity. Minimum requirements

for larval growth were 25O to 3o”c

(77O to 86OF) and 20- to 35-ppt salinity. Larval growth was maximized at

25OC and 25 ppt salinity (Tettelbach

and Rhodes 1981). Tettelbach and

Rhodes (1981) also gave multiple

regression equations for predicting

larval survival through 5 days, larval

survival through 8 days (settlement),

3

larval growth through 5 days, and

larval growth through 8 days, from

temperature and salinity of the rearing environment.

Water Currents

Water currents seem to influence

food availability, waste removal,

growth rate, larval movements, and

distribution of juvenile settlements

(Broom 1976; Robert 1978). KirbySmith (1972) found that scallops grew

best in water currents less than 1

cm/s (0.03 ft/s); maximum growth

occurred at 0.21 cm/s (0.007 ft/s).

Scallop growth ceased at a water

velocity of 12 cm/s (0.4 ft/s).

Adductor muscle (the edible portion of

scallops) quality was higher at slow

currents compared to fast currents.

Food availability was interrelated with

current and growth, and growth

decreased if adequate food (given as

1.2 ug/l chlorophyll a) was not available, even at the slowest current

speeds. Cooper and Marshall (1963)

reported that although the densest of

four scallop beds studied was in an

area with the highest current velocity, scallops in slower currents had

the higher condition factors.

Water currents probably influence

the directional movements and distribution patterns of planktonic life

stages of the bay scallop (Moore and

Marshall 1967; Merrill and Tubiash

1970). However, once bay scallops

reach the adult stage, water currents

play a lesser role in influencing movement, though they may cause apparent

directionality of movement in otherwise

random individual scallop movements

(Moore and Marshall 1967; B room

1976).

Turbidity

Stone and Palmer (1973) demonstrated that bay scallops exposed to

1000 ppm turbidity (clay particles) for

several weeks showed a 19% reduction

in dry weight compared to control
animals. At 500 ppm, filtering rates

of bay scallops decreased 35% compared to controls. Stone and Palmer

(1973) suggested that long-term exposure to levels of turbidity greater

than 500 ppm may interfere with normal growth and reproductive processes

of bay scallops.

Substrate

The availability of appropriate

substrates for settlement, attachment,

and feeding activity is essential. Beds

of eelgrass and other seagrasses

growing on sand substrates are preferred (Belding 1910). Soft mud and

silt substrates are harmful to the survival of settling juveniles, but only if

juveniles do not first attach directly

to seagrass for a short period of

growth before dropping to the bottom

(Castagna 1975). Extremely thick

seagrass beds, with no open spaces,

cut off water circulation entirely and

are detrimental to settling juvenile

scallops (Belding 1910).

Oxygen Requirements

Resting requirements of oxygen

for adult bay scallops averaged 70

ml/kg/hr at 20°C (68OF), a value

comparable to that of other temperate

bivalves possessing strong swimming

powers (Van Dam 1954). Rate of

oxygen uptake was independent of

dissolved oxygen concentration down

to a level of 1.5 ppm. Percentage of

available dissolved oxygen removed by

scallops ranged from 0.5% to 13% (Van

Dam 1954).

Heavy Metals

Ninety-six hour LC5,, values for

juvenile bay scallops exposed to silver, mercury, and cadmium were 33

ppb, 89 ppb, and 1480 ppb, respectively (Nelson et al. 1976). Scallops

surviving after 96 hr of exposure to

940 ppb cadmium and 22 ppb silver

had significant uptake ,of these metals

in all body tissues. Exposure to LC25

and LC, concentrations of cadmium

caused higher oxygen consumption

compared to control animals. Juvenile

scallops exposed to LC,,concentrations

of silver also had higher oxygen consumption, but those exposed to LCS

concentrations did not exhibit this

reaction (Nelson et al. 1976).

14
LITERATURE CITED

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(U.K.) 46: 33-47.

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1983. Growth and reproduction of

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Belding, D. L. 1910. The scallop

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Castagna, M. 1975. Culture of the bay

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15
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the pea crab, Pinnotheres maculatus, on growth of the bay scallop. Chesapeake Sci . 13:

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16
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130: 118134.

Sastry, A. N. 1968. The relationships

among food, temperature, and

gonad development of the bay

scallop. Physiol. Zool. 41: 44-53.

Sastry, A. N. 1970a. Reproductive

physiological variation in latitudinally separated populations of the

bay scallop. Biol. Bull. (Woods

Hole) 138: 56-65.

Sastry, A. N. 1970b. Environmental

regulation of oocyte growth in

the bay scallop. Experientia 26:

1371-1372.

Sastry, A. N., and N. J. Blake.

1971. Regulation of gonad development in the bay scallop. Biol.

Bull. (Woods Hole) 140: 274-283.

Sastry, A. N., and R. W. Menzel.

1962. Influence of hosts on the

behavior of the commensal crab,

Pinnotheres maculatus. Biol,

Bull. (Woods Hole) 123: 388-395.

Stone, R., and R. Palmer. 1973.

Effects of turbidity on the bay

scallop. Northeast. Univ. Mar.

Sci. Inst. Contrib. No. 38. 8 pp.

Tettelbach, S. T., and E. W. Rhodes.

1981. Combined effects of temperature and salinity on embryos

and larvae of the northern bay

scallop. Mar. Biol. 63: 249-256.

Thayer, G. W., and H. H. Stuart.

1974. The bay scallop makes its

bed of seagrass. Mar. Fish. Rev.

36(7): 27-30.

Turner, H. J., Jr., and J. E.

Hanks. 1960. Experimental stimulation of gametogenesis in

Hydroides dianthus and Pecten

irradians during the winter.

Biol . Bull. (Woods Hole) 119:

145-152.

Van Dam, L. 1954. On the respiration

in seal lops. Biol. Bull. (Woods

Hole) 107: 192-202.

Vernberg, F. J., C. Schlieper, and

D. E. Schneider. 1963. The

influence of temperature and

salinity on ciliary activity of

excised gill tissue of mollusks

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Suppl. to No. 5, Mem. 3: 1-125.

17
0272 -I01

REPORT DOCWfENTATlON ?,R-‘ORT NO. 2. 3. Recipient’s Accession No.

PAGE FWS/OBS-82/11.12 *

. Title and Subtitle Species profi 1 es : Life Histories and Environmental 5. RFporf oat.?

Requirements of Coastal Fishes and Invertebrates (Mid-Atlantic) -- October 1983

Bay Scallop 6.

- - ‘. Author(s) 8. Performing Organization Rept. No.

Clemon W. Fay, Richard J. Neves, and Garland B. 

____~

Pardue

1. Performing Organization Name and Address 10. Project/Task/Work Unit No.

Department of Fisheries and Wildlife Sciences

Virginia Polytechnic Institute and State University 11. ContracX) or Grant(G) No.

Blacksburg, VA 24061 (C)

(G)

12. Sponsoring Organization Name and Address

National Coastal Ecosystems Team

13. Type of Reporf & Period Covered

U.S. Army Corps of Engineers

Fish and Wildlife Service Waterways Experiment Station

U.S. Department of the Interior P.O. Box 631

Washington, DC 20240

14.

Vicksburg, MS 39180

L5. Supplementary Notes

*U.S. Army Corps of Engineers report No. TR EL-82-4.

.

IC. Abstract (Limit: 200 words)

Species profiles are literature summaries of the taxonomy, morphology, range, life

history, and environmental requirements of coastal aquatic species. They are prepared to

assist in environmental impact assessment. The bay scallop (Argopecten irradians) is a

commercially and ecologically important scallop of estuarine and inshore environments,

from Cape Cod, Massachusetts, to Laguna Madre, Texas. They occur at depths from 0.3 to

18 m but are most common in waters less than 2 m deep. They spawn at 1 year of age

from April through December, later in southern populations. Water temperature and food

supply are important factors for proper gonad development and spawning. Larvae are

planktonic, and juveniles settle and attach by byssal threads to suitable substrates;

seagrass beds are preferred for settlement. Bay scallops are filter feeders, consuming

primarily benthic diatoms. Temperature, salinity, water currents, and availability of

suitable attachment/settlement substrates are the most important environmental requirements of bay scallops. They require a minimum water temperature of 20°C for spawning, and

a minimum of 14 ppt salinity, grow best in currents less than 1 cm/s, and prefer eelgrass

t0 other seagrasses for settlement and attachment during early life stages.

17. Document Analysis a. Descriptors

Scallops Growth

Feeding Estuaries

Shellfish

b. Identifiers/Dpen.Ended Terms

Bay scallop Life history

Argopecten irradians Spawning

Salinity requirements

c. COSATI Field/Group

8. Availability Statement / 19. Security Class (This Report) 21. NJ. of pages

Unlimited Unclassified ____ 17 __-

22. Price

OPTIONAL FORM 272 (4-7;

(Formerly NTIS-35)

Department of Commerce
Species proiiies :

Research Library

U.S. Department of the Interior

National Biological Service

sion of Biological

. . . . . ..ngton. DC

K Eastern Energy and Land Use Team __._ .._ ,.,,,

+ National Coastal Ecosystems Team

0 Western Energy and Land Use Team

l Locations of Regional Offices

REGION 1

Regional Director

U.S. Fish and Wildlife Service

Lloyd Five Hundred Building, Suite 1692

500 N.E. Multnomah Street

Portland, Oregon 97232

REGION 4

Regional Director

U.S. Fish and Wildlife Service

Richard B. Russell Building

75 Spring Street, S.W.

Atlanta, Georgia 30303

REGION 2 REGION 3

Regional Director Regional Director

U.S. Fish and Wildlife Service U.S. Fish and Wildlife Service

P.O. Box 1306 Federal Building, Fort Snelling

Albuquerque, New Mexico 87 103 Twin Cities, Minnesota 55 I 11

REGION 5

Regional Director

U.S. Fish and Wildlife Service

One Gateway Center

Newton Corner, Massachusetts 02 158

REGION 6

Regional Director

U.S. Fish and Wildlife Service

P.O. Box 25486

Denver Federal Center

Denver, Colorado 80225

REGION 7

Regional Direct01

U.S. Fish and Wildlife Service

1011 E. Tudor Road

Anchorage, Alaska 99503
DEPARTMENT OF THE INTERIOR

U.S. FISH AND WILDLIFE SERVICE

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fostering the wisest use of our land and water resources, protecting our fish and wildlife,

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