REFFnE"T" COPY 

Do Not Remove from the Library 

U. S. Fish and Wildlife Service 

Biological Report 82 (1 1.67) 

~ugust 1986 700 Cajun Dome Boulevard 

Lafayette, Louisiana 70506 

Species Profiles: Life Histories and 

Environmental Requirements of Coastal Fishes 

and Invertebrates (North Atlantic) 

SEA SCALLOP 

Coastal Ecology Group 

Fish and Wildlife Service Waterways ~xperiment station 

U.S. Department of the Interior U.S. Army Corps of Engineers 
Biological Report 82(11.67) 

TR EL-82-4 

August 1986 

Species Profiles: Life Histories and Environmental Requirements 

of Coastal Fishes and Invertebrates (North Atlantic) 

SEA SCALLOP 

Dennis M. Mullen 

and 

John R. Moring 

Maine Cooperative Fishery Research Unit 

313 Murray Hal 1 

Uni vers i ty of Mai ne 

Orono, ME 04469 

Project Manager 

Carroll Cordes 

Project Officer 

David Moran 

National Wet1 ands Research Center 

U.S. Fish and Wildlife Service 

1010 Gause Boulevard 

Slidell, LA 70458 

This study was performed for 

Coastal Ecology Group 

U.S. Army Corps of Engineers 

Waterways Experiment Station 

Vicksburg, MS 39180 

and 

National Wetlands Research Center 

Fish and Wildlife Service 

U.S. Department of the Interior 

Washington, DC 20240 
This series should be referenced as follows: 

U.S. Fish and Wildlife Service. 1983-19-. Species profiles: life 

histories and envi ronmental requi rements of coastal fishes and 

invertebrates. U.S. Fish Wildl. Serv., Biol. Rep. 82(11). U.S. Army 

Corps of Engineers, TR EL-82-4. 

This profile should be cited as follows: 

Mullen, D.M., and J.R. Moring. 1986. Species profiles: life 

hi stories and environmental requi rernents of coastal fishes and 

invertebrates (North Atlantic) -- sea scal lop. U. S. Fish Wi ldl . Serv. Biol. Rep. 82(11.67). U.S. Army Corps of Engineers, TR EL82-4. 13 pp. 
PREFACE 

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

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

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 may be 

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

profile has sections on taxonomy, 1 ife history, ecological role, environmental 

requirements, and economic importance, if appl icable. A three-ri ng binder is 

used for this series so that new profiles can be 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 one of 

the foll owing addresses. 

Information Transfer Specialist 

National Wetlands Research Center 

U.S. Fish and Wildlife Service 

NASA-Slidell Computer Complex 

1010 Gause Boulevard 

Slidell, LA 70458 

U. S. Army Engineer Waterways Experiment Station 

Attention: WESER-C 

Post Office Box 631 

Vicksburg, MS 39180 
CONVERSION TABLE 

Metric to U.S. Customary 

mil 1 ineters (mn) 

centimeters (an) 

meters (m) 

ki 1 ometers ( km) 

2 

square meters (m ) 10.76 

square ki 1 meters ( km2) 0.3861 

hectares (ha) 2.471 

liters (1) 

cubic meters (m3) 

cubic ~neters 

mil 1 igrams (mg) 0.00003527 

grams (9) 0.03527 

kilogralns (k ) 2.205 

metric tons qt) 2205.0 

metric tons 1.102 

ki 1 ocal ories ( kcal ) 3.968 

To Obtain 

inches 

inches 

feet 

mil es 

square feet 

square nil es 

acres 

gal 1 ons 

cubic feet 

acre-feet 

ounces 

ounces 

pounds 

pounds 

short tons 

British thermal units 

Cel sius degrees 1.8(OC) + 32 Fahrenheit degrees 

U.S. Customary to Metric 

inches 25.40 

inches 2.54 

feet (ft) 0.3048 

fathoms 1.829 

miles (mi) 1.609 

nautical miles (mi) 1.852 

square feet (ft2) 

acres 2 

square miles (mi ) 

gal 1 ons ( gal ) 

cubic feet (ft3) 

acre-feet 

ounces (02) 28.35 

pounds (lb) 0.4536 

short tons (ton) 0.9072 

British thermal units (Btu) 0.2520 

mil 1 imeters 

centimeters 

meters 

meters 

kil ometers 

ki 1 oaeters 

square meters 

hectares 

square kil ometers 

1 i ters 

cubic meters 

cubic meters 

grams 

kil ograms 

metric tons 

ki 1 ocal ori es 

Fahrenheit degrees 0.5556("F - 32) Celsius degrees 
CONTENTS 

PREFACE ....................... CONVERSION TABLE .................. ACKNOWLEDGMENTS .................. 

NOMENCLATURE /TAXONOMY/RANGE ............. MORPHOLOGY /IDENTIF ICATI ON AIOS ........... Adult ..................... Juveni 1 e .................... REASON FOR INCLUSION IN SERIES ........... LIFEHISTORY .................... Spawning .................... Fecundity and Eggs ............... Larvae ..................... Adult ..................... THE FISHERY ..................... GROWTH CHARACTERISTICS ............... POPULATION DYNAMICS ................. ECOLOGICAL ROLE ................... Feeding Habits ................. Predat i on ................... Symbiosis ................... ENVIRONMENTAL REQUIREMENTS ............. Temperature .................. Sal i ni ty .................... 

LITERATURE CITED .................. 

Page 

i i i 

i v 

vi 

1 

3 

3 

3 

3 

3 

3 

4 

4 

5 

5 

8 

8 

9 

9 

9 

9 

10 

10 

10 
ACKNOWLEDGMENTS 

We thank Herbert Hidu, Ira C. Darling Center, University of Maine, and Clyde 

L. MacKenzie, Jr. , National Marine Fisheries Service, Sandy Hook Laboratory, New 

Jersey, for reviewing the manuscript. Figure 1 is used with the permission of 

Mr. MacKenzie. 
Figure 1. Sea scallop (Placo~ecten rnaqel lanicus). 

SEA SCALLOP 

NOME NC LATUR E/TAXONOMY /RANGE 

Scientific name ...... Placopecten 

magel 1 ani cus (Gmel i n) 

Preferred common name ... Sea scallop 

(Figure 1) 

Other common names ... Atlantic deep 

sea scallop, giant scallop, ocean 

scallop, smooth scallop 

Phylum ..................... Mollusca 

Class ...................... Rivalvia 

Order ..................... Pterioida 

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

Geographical range: The sea s c a l l o p 

inhabits Atlantic coastal waters 

from the Gulf of St. Lawrence 

(Posgay 1957) to Cape Hatteras, 

North Carolina (Porter 1974). 

Sea scallops are most abundant on 

Georges Rank and the Mid-At1 antic 

shelf, and less abundant along 

the coast of Maine, the Bay of 

Fundy, and the Gulf of St. 

Lawrence (MacKenzie 1979). North 

of Cape Cod, the sea scallop 

lives just below the low tide 

mark and, on occasion, intertidally along the coast of Maine 

(MacKenzie 1979). South of Cape 

Cod, it is restricted to deeper, 

cooler waters. Sea scal lops 

rarely occupy waters deeper than 

110 m (Posgay 1979). Scallops 

a re comnerci a1 ly harvested over 

their entire range (see Figure 2 

for the North Atlantic region 

distribution of the sea scallop). 
p Princlpai estuarine fisheries 

MILES 

KILOMETERS 

A Tl A N TIC OCEAN 

Figure 2. Coastal distribution of the sea scallop (Placopecten magellanicus). 
MORPHOLOGY/IDENTIFICATION AIDS REASON FOR INCLUSION IN SERIES 

The following is summarized from 

MacKenzi e (1979). 

Adult 

The shel 1 of the adult sea 

scallop is large, 12.5 to 20.0 cm 

long, subcircular, and compressed. 

(Length is defined as the farthest 

distance across the shell on a line 

parallel to the hinge line. Height is 

the farthest distance across the shell 

perpendicular to the hinge line. 

Width is the distance from the top to 

the bottom across both shel 1s.) The 

two valves are subequal, hinged 

dorsally, and meet along the ventral 

margin, except for a small gap between 

them near the dorsal hinge line. The 

right valve rests on the bottom. 

Radial ribs are present along with 

concentric 1 amel 1 ae or growth 1 i nes . This sculpturing is more prominent on 

the left valve. The left valve is 

usually reddish-brown in color but may 

be lavender or yellow. The right 

valve is pale cream or white. The 

wings on the left valve are nearly 

equal; the wings on the right valve 

differ in that the anterior wing 

contains a byssal notch. The inner 

surface is lustrous and smooth with 

distinct adductor muscle and pal 1 ial 

scars (roughened areas may be present 

due to secretions laid down to repair 

damage from boring organisms). The 

adductor mscle scar is located 

slightly posterior and dorsal to the 

center of the valves and is slightly 

larger on the left valve. 

Juvenile 

Most juvenile sea scallops, 5 mm 

long and larger, resemble the adults. 

The valves are higher than long, with 

a less noticeable gap near the dorsal 

hinge-line. The sculpturing is more 

pronounced on the left valve; radial 

1 ines are lacking on the right valve. 

The adductor muscle scar is well off 

center. 

The sea scallop supports one of 

the most valuable shellfisheries 

(second only to the American lobster 

in 1982) along the United States 

eastern seaboard. In 1982, 21.3 

million pounds of shucked sea scallops 

worth $78.1 mi 11 ion were 1 anded in the 

United States (Thompson 1983). North 

of Cape Cod, sea scallops are highly 

valued by scuba divers. 

In some waters, sea scallops are 

commonly overfished and those near 

industrial centers are exposed to 

contaminants. Little is known about 

the life history and environmental 

requirements of the sea scallop. 

LIFE HISTORY 

Spawning 

Sea scallops in Port au Port Bay, 

Newf oundl and, reach sexual maturity 

and spawn for the first time at age 1, 

just after the formation of the first 

growth ring (Naidu 1969). Sexes are 

usually separate. Examples of 

exceptions are two hermaphrodites 

among about 3,000 scal 1 ops exami ned 

from Georges Bank waters (Merrill and 

Burch 1960) and 42 of about 3,000 

examined from Port au Port Bay, 

Newfoundland (Naidu 1970). In 1975, 

the sex ratio reported for Georges 

Bank in 1975 was 1:1, but the ratio 

for the Middle Atlantic shelf was 1.4 

males to 1 female (MacKenzie et al. 

1978). 

Spawning season occurs later as 

one moves from south to north and has 

been reported as July along North 

Carolina and Vi rgi ni a coasts (Serchuk 

et al. 1969), as late July to 

mid-August offshore on the shel f 

(MacKenzie et al. 1978), as late 

September near the Isles of Shoals, 

New Hampshire (Cull i ney 1974), and 

late September or early October in 

the Georges Bank area (Posgay and 

Norman 1958). Two spawning seasons 
were reported for Port au Port Bay, 

Newfoundland: a small one in early 

summer and a much larger one lasting 

from late August to October (Naidu 

1970). The temperature during 

spawning a1 so varies among 1 ocations. 

In 1966, scallops spawned in Port au 

Port Bay as temperatures fell from 

16.1 to 4.2 OC (Naidu 1970). In 1973, 

scallops spawned when the water temperature was 14 OC in the Isles of 

Shoals waters, and 10 OC in the laboratory (Culliney 1974). In 1975, 

spawning temperatures ranged from 9 to 

11.2 OC in Georges Bank waters and 

from 6.5 to 11 OC in Middle Atlantic 

shelf waters (MacKenzie et al. 1978). 

The duration of the spawning season 

has been reported to be as short as 

1 week in Georges Bank waters (Posgay 

1979) and as long as 5 weeks in Port 

au Port Bay (Naidu 1970). 

Fecundity and Eggs 

A female .scallop releases as many 

as one million eggs a year. The 

larger the female the more eggs 

produced (MacKenzie 1979). The eggs 

are fertilized in the water after mass 

spawning. Spawning in the fall may be 

triggered by a rise in bottom water 

temperature that follows the breakdown 

of the thermocline (Posgay 1979). 

Dickie (1955) attributes the onset of 

spawning to tidal cycles, and Naidu 

(1970) observed that spawning usually 

coincides with strong onshore winds 

and rough seas. Naidu postulates that 

spawning may be initiated by prolonged 

exposure to physical shocks. 

Sea scallop eggs are 64 microns 

in diameter and pink and brown in 

color. In the laboratory, the eggs 

hatch within 30 to 40 hours of 

fertilization at 15 OC and 32 ppt 

salfnity (Culliney 1974). The eggs 

and larvae are planktonic (Merri 11 

1961). 

Larvae 

Little is known about the length 

of the planktonic larval stage of the 

sea scal lop. The following observati ons were drawn from 1 aboratory 

studies by Culliney (1974). Thirty to 

40 hours after spawning, sea scallop 

embryos hatch into motile ciliated 

gastrulae that average 69 microns long 

and 63 microns high. By the fourth 

day, the young scallops become typical 

she1 led straight-hinge vel i gers that 

average 105 microns long and 82 

microns high. Development takes place 

at water temperatures from 12 "C to 18 

"C. By 13 days, the larvae reach a 

length of 175 microns and a height of 

150 microns. 

On the 23rd day of development, 

typical bi val ve vel i ger eyespots 

appear and, by the 28th day, over 50% 

of the larvae possess a functional 

foot characteristic of the presettl i ng 

pediveliger stage. Pediveliger larvae 

are about 279 microns long and 242 

microns high . 

Scallop larvae remain planktonic 

for over a month after hatching 

(Posgay 1979). The first spatfall of 

laboratory-spawned 1 arvae was 35 days 

after hatching (Cull iney 1974). 

Planktonic scallop larvae in the sea 

may be transported out of the spawning 

area by predominant currents (Posgay 

1979). This observation led Posgay 

(1979) to postulate that none of the 

large North At1 antic scallop 

populations (with the exception of the 

Georges Bank population) are self 

populated by their own larvae and 

spat. For example, spatfall on the 

Continental Shelf opposite Chesapeake 

Bay may come from larvae spawned from 

scallops on the Continental Shelf 

opposite Delaware Bay. This area, in 

turn, may receive its spatfall from 

scallops on the shelf opposite the 

mouth of the Hudson River, which may 

be populated by larvae escaping from 

Georges Bank. Georges Bank has a 
semipersistent gyre that probably 

retains most larvae produced there; 

consequently, sea scallop populations 

on Georges Bank might be self 

repopulating. Based on spat settling 

behavior observed in the 1 aboratory, 

pedivel igers develop a thick strong 

byssus and crawl around extensively in 

search of a hard surface for 

attachment (Cull i ney 1974). The spat 

attach themselves to the underside of 

shell fragments and other solid 

materials on the bottom. This 

behavior may protect the spat from 

epi benthic predators, such as crabs. 

Once attached, the pedi vel i gers begin 

metamorphosis into the adult form. 

The larvae are able to delay 

metamorphosis for up to 1 month while 

searching for appropriate substrate 

(Cu 11 i ney 1974). 

Recause scallop spat attach to 

navigation buoys 1 ocated only in areas 

of the buoys that were free of other 

mol lusks, Merri 11 and Edwards (1976) 

concluded that scallops do not compete 

well with the other mollusks for food 

or space. Young s c a l l o p s frequently 

settle on the bryzoan, Gemelleria 

(Bai rd 1953). It is believed that sea 

scal lops prefer shell fragments and 

other animals for setting because 

young scallops are unable to survive 

on shifting sand bottoms (Merrill and 

Edwards 1976). 

Adu 1 t 

Young adults larger than 10 mm 

long detach from the epibenthic 

substrate and settle on the bottom 

(Dow 1969). Scal lops are re1 at i vely 

active until they are about 8 cm long, 

swimmi ng in response to disturbances 

such as predation (Bai rd 1954) and 

commercial dredging (Caddy 1968). 

Scallops swim by rapidly closing 

the valves and forcing water through 

ports situated on the wings. Swimning 

scallops move through the water with 

the hinge aft. Each contraction moves 

the scallop about 125 cm (Posgay 

1950). Some move at ground speeds of 

67 cm/sec for distances up to 4 m 

(Caddy 1968), and, while swimming, 

scallops may be carried long distances 

by currents. Currents may be a means 

of migration for smaller scallops 

(Bai rd 1954). 

Large adult scallops ( > 9 cm 

long) do not migrate (Baird 1954; 

Caddy 1968; Posgay 1981). Large 

scallops are recessed in the sediment 

and do not usually move unless 

physically disturbed (Caddy 1968). 

THE FISHERY 

The U.S. commercial scallop 

fishery began in 1884 with the 

discovery of several nearshore scallop 

beds near Mount Desert Island, Maine 

(Smith 1891 ) . The U.S. fishery 

operated on a small scale until the 

1930's when the large scallop beds of 

Georges Bank began to be heavily exploited. Canadian fishermen entered 

the Georges Bank scallop fishery in 

the mid 19501s, and by the mid 1960's 

they took more scallops than the U.S. 

fishermen (Serchuk et al. 1969). In 

those years the U.S. scallop fleet 

concentrated on the scallop stocks of 

the Mid-Atlantic she1 f (Posgay 1968). 

Scal1 ops reach a commercially 

attractive size in their fifth or 

sixth year of life when they comprise 

over 90% of the landings (Posgay 

1982). The success or failure of a 

particular year class can have a major 

effect on the commercial catch 5 to 

6 years later. Fluctuating year-class 

strengths probably account for the 

large fluctuations in the quantity of 

scallops landed from one year to the 

next (Table 1). 

The U.S. landings of sea scallop 

meats in 1982 were 9,693 metric tons 

valued at $78.1 million. Canada, the 

only other country to extensively 

gather harvest scallops within the 

U.S. Fishery Conservation Zone in 
Table 1. U. S. and Canadian sea scallop landings (metric tons of 

meat) from Canada and the northeast U.S. coast, 1887-1982 

(source: International Commission for North Atlantic Fisheries: 

Subarea 5 and Statistical Area 6). 

Year 

1887 a 

1888 

1889 

1892 

1897 

1898 

1899 

1900 

1901 

1902 

1903 

1904 

1905 

1906 

1907 

1908 

1909 

1910 

1911 

1912 

1913 

1914 

1916 

1919 

1921 

1924 

1926 

1928 

1929 

1930 

1931 

1932 

1933 

1934 

1935 

1937 

1938 

1939 

1940 

1941 

1942 

USA Year USA Canada Total 

a Data for 1877-1977 taken from Serchuk et al. (1979). 

b~ata for 1978-82 taken from Thompson (1980, 1981, 1982, 1983). 
1982, landed 4,312.4 metric tons 

(Thompson 1983). Over 75% of all 

scallops landed in the United States 

in 1982 were landed in New England 

states, and most of those were landed 

in Massachusetts (Table 2). 

The sea scallop is gathered 

commercially over its entire range, 

wherever its abundance is sufficiently 

high. Maine is the only State (or 

Province) that imposes a season 

(November 1 to April 14) in its 

territorial waters. 

operated from vessels in Georges Bank 

and Mid-Atlantic Shelf waters are 

about 3-4 m wide (MacKenzie 1979). In 

some inshore waters in Maine and 

Canada, where the bottom is gravelly 

and rocky, dredges 1-1.3 m wide are 

towed as singles, doubles, or 

triples. Caddy (1968) observed 

dredge efficiency and found that 

dredges are more efficient in 

capturing the large, less active 

scallops and less efficient in 

capturing the small er, more active 

scal lops. 

Scallops are usually fished with In rocky nearshore areas, scuba 

dredges. Dredge size and type varies divers gather scallops commercially 

with locality. Sca 1 1 op dredges (Walton 1979). The catch is sold to 

Table 2. Sea scallop landings (in thousands of pounds and thousands 

of do1 lars) and price per pound for the New England States, 1977-82 

(National Marine Fisheries Service, unpubl. data). 

Year 

State 73 /7 1978 1979 1980 1981 1982 

Connecticut 

lb 9 4 94 198 - - 5 0 

Do1 lars 160 160 493 - - 250 

Price/l b $1.70 $1.70 $2.49 - - $5 .OO 

Maine 

lb 39 5 908 1,163 - 3,734 1,733 

Do1 1 ars 7 54 2,246 3,878 - 15,095 6,810 

Price11 b $1.91 $2.47 $3.33 - $4.04 $3.93 

Massachusetts 

lb 16,322 16,141 14,114 11,799 14,453 13,762 

Do1 1 ars 27,240 40,931 47,908 47,313 59,213 49,112 

Pri cell b $1.65 $2.54 $3.39 $4.01 $4.10 $3.57 

New Hampshire 

lb - - 6 0 49 - - 

Do1 1 ars - - 196 200 - - 

Price11 b - - $3.27 $4.08 - - 

Rhode Island 

lb 100 355 764 1,815 - 318 

- Dollars 157 974 2,703 6,892 - 1,075 

Price11 b $1.57 $2.74 $3.54 $3.80 - $3.38 
local restaurants and tourists but no 

catch data are reported. Scuba divers 

are subject to the same open season 

(November 1 to April 14) as commercial 

fishermen. 

GROWTH CHARACTER1 STICS 

The age and growth rate of 

scallops are calculated by reading 

annual rings formed on the shell in 

early spring (Posgay 1979), or 

empirically by tagging, releasing, and 

recapturing 1 ive scallops (Merrill et 

al. 1966). The first identifiable 

ring is formed when the scallop is 1.5 

years old and about 20 mm long. The 

first actual ring is formed when the 

scallop is 0.5 year old and about 7 mm 

long but this ring is weak and rapidly 

wears off (Posgay 1979). Growth in 

the first several years is rapid. 

Retween the 3rd and 5th years of 1 ife, 

the height of the scallop increases 

about 50% to 80% and meat weight 

increases up to 400%. Scallops in age 

group 7 provide maximum yields of 

rneat per scallop in the waters of 

Georges Bank and the Mid-Atlantic 

shelf (MacKenzie 1979). After age 8, 

the annual growth increment falls to 

less than 10% per year (Serchuk et al. 

1969). The age-hei ght re1 ationship of 

the sea scallop for the coast of Maine 

(Dow 1969) is as follows: 

Age (year) Height (mm) 

0.5 2 

These average heights of scallops the 

same age are slightly smaller than 

'those reported by Serchuk et al. 

(1969) for Georges Bank, the Gulf of 

Maine, and the Mid-Atlantic shelf. 

POPULATION DYNAMICS 

Little is known about the density 

and distribution of planktonic sea 

scallop larvae. The abundance of 

juveniles has been estimated by 

sampling spatfalls (Larsen and Lee 

1978) and by calculating juvenile 

densities on navigation buoys (Merri 11 

and Edwards 1976). Samples of 

spatfalls from the Nantucket Shoals 

1 ightship buoy revealed a juvenile 

scal 1 op density of 392/m2. Scal 1 ops 

ranged in height from 0.5 mm (just 

settled) to 13.2 mm (about one year 

old) according to Merrill and Edwards 

(1976). In contrast, a 5-minute tow 

with a scallop dredge over the substrate below the buoy collected only 

7 adult scallops. The estimated spat 

density at Georges Bank in February 

of 1977 ranged from 2 to 123/m2. In 

May, the density was about 2 to 63 

spat/m2. 

The percentages of adult scal 1 ops 

at different depths (Table 3) were 

determined from samples from 144 

stations in the Georges Bank waters in 

1975, and 57 stations on the Middle 

Atlantic shelf (MacKenzie et al. 

1978). 

Table 3. The percentage of adult 

scallops at different depths, 

adjusted to equal sampling intensity, 

for Georges Bank and Middle Atlantic 

shelf waters in 1975. 

Sampling area Depths (m) Percentage 

Georges Bank 37 to 50 13 

51 to 75 54 

76 to 100 33 

Middle Atlantic 

shelf 31 to 50 2 5 

51 to 75 7 5 

76 to 80 (0.5 
In 1960, the density of adult 

scallops was about 1 per square meter 

for the 274 km2 northern edge of 

Georges Bank (Caddy 1971). The 

population estimate was about 270 

mill ion. Scallop density varies with 

substrate. In 1967, in the Northumberland Strait of the Gulf of St. Lawrence, estimated densities were 4.2 

adult scal lops/m2 on sandy bottoms and 

1. 4/m2 on mud bottoms. 

An equation for estimating 

natural mortality was proposed by 

Dickie (1955). His method is based on 

the observation that the two valves 

(clappers) of dead scallops remain 

attached for a known period (Merrill 

and Posgay 1964). Natural mortality 

is computed by the equation: 

C is the number of pairs of attached 

clappers in the sample, L is the 

number of live scallops in the sample, 

and t is the average time in weeks 

that the clappers remai n attached. 

From this equation, Merrill and Posgay (1964) obtained an instantaneous 

natural mortality of 0.1045 for 

Georges Bank scallops. This value 

translates into an annual natural 

physiological mortality of 9.9%. 

ECOLOGICAL ROLE 

Feeding Habits 

Larval scallops were raised on a 

diet of the phyt~~lankter, Isochrysis 

gal bana , at concent rations rangi ng 

from 5,000 to 50,000 cells/ml 

(Culliney 1974). Spat were raised on 

a mixture of I. galbana and Chrosomonas salina at a concentration of 

about l~cells/ml. Adult scallops 

are filter feeders, feeding on plankton and organic detritus (MacKenzie 

1979). Adults have been kept a1 ive on 

a diet of the diatom Phaeodact lum 

tricornutum (Bourne 1964- 

Predation 

A list of known predators of 

larval sea scallops includes a wide 

variety of p 1 ankti vores (MacKenzie 

1979). The major natural predators of 

juvenile and adult scallops are as 

fol lows: rock crab, Cancer i rroratus, 

lobster, Homarus ameri canus vd 

Jamieson 1979; Jamieson et al. 1982), 

starfish, Asterias vulgaris (Caddy 

1968, 1973; Dickie and Medcof 1963; 

Dow 1969; Medcof and Bourne 1964), 

and Crossaster papposus (Medcof and 

Bourne 1964), moonsnai 1 , Lunatia 

heros (Dickie and Medcof 19- 

burrowing anemone, Ceriantheo si s 

ameri canus (MacKenzi e 1 9nTj3dk 

cod, Gadus morhua, Ameri can plaice, 

Hi o Zoides latessoides, and 

-i sh ,bs 1 upus 

(Medcof and Bourne 1964). 

According to Caddy (1968, 1973), 

scallops that had been injured by 

commercial drag operations are preyed 

upon by several species of qround 

fish, e.g. the scul~ins, ~~oxocephalus 

sp., and the winter flounder. 

Pseudopl euronectes americanus. ~ab: 

oratory studies show that juvenile 

lobsters prey on scallops larger than 

themselves, and that prey size tends 

to increase with the size of the predator (Elner and Jamieson 1979). 

Because of the large size of adult 

scallops, rock crabs and lobsters feed 

more on the smaller, more abundant 

juveni le scal lops (Jamieson et a1 . 1982). 

Symbiosis 

A form of commensalism has been 

reported between the sea scallop and 

the juvenile red hake Uro h cis chuss 

(Goode 1884). Small h+k~ 

12 cm) live inside the mantle cavities 

of sea scallops (Wigley and Theroux 

1971). Scallops less than 110 mm high 

apparently are too small, and scallops 

longer than 300 mm are too large to 

harbor juvenile hake (Wigley and 

Theroux 1971; Garman 1983)- Hake 
larger than 300 mm seem to require 

thigmotactic security and live outside 

the scallops but touching them. The 

importance of this association is not 

clearly understood, but it may have 

some biological benefits to one or 

both species (Garman 1983). 

ENVIRONMENTAL REQUIREMENTS 

Sea scal 1 ops spawn at 

temperatures between 14 and 16 OC in 

New Hampshire, and between 10 and 

15 OC in the laboratory (Culliney 

1974). Scallops spawn in Newfoundland 

at temperatures between 4.2 and 

16.1 OC (Naidu 1970). Spawning may be 

triggered by a rapid drop in temperature in the fa1 1 (Posgay 1979). A 

strong correlation (r = 0.8) has been 

found between the temperature at the 

time of spawning and commercial 

landings 6 years later (Dow 1971; 

Sutcliffe et al. 1977; Caddy 1979). 

This correlation is strong evidence 

that water temperature is a dominant 

factor in determining spawning success 

and year class abundance. Excessi vely 

low summer temperature may delay or 

even prevent spawning and larval 

development (Medcof and Bourne 1964). 

Little is known about the 

importance of water temperature on 

larval survival and development. 

Larvae raised under laboratory 

conditions grew well at a temperature 

of 15 "C, but few survived at 19 OC 

(Cu 11 i ney 1974). 

The high lethal temperature for 

adult sea scallops ranges from 20 to 

24 OC, depending on the acclimation 

temperature (Dickie 1958; Posgay 

1953). The 20 OC isotherm largely 

determines the southern distribution 

of sea scallops (MacKenzie 1979). A 

sudden rise in water temperature over 

scallop beds can induce mass 

mortality. (Merri 11 and Posgay 1964). 

The optimum temperature for the growth 

of adult sea scallops is 10 "C. 

Growth rates drop 5% at 8 OC and 20% 

at 12 OC. Mean annual temperatures 

for Georges Bank waters range from 8" 

to 12 OC (Merrill et al. 1961). 

Salinity 

Sea scallops usually inhabit 

waters with salinities characteristic 

of oceanic waters (MacKenzie 1979). 

Salinity tolerances of adult sea 

scallops have not been studied, but 

Cull i ney (1974) examined the effects 

of different salinities on scallop 

larvae by moving larvae from sea water 

(32 ppt salinity) into water of the 

test salinity. Larvae exposed to a 

salinity of 10.5 ppt for 42 h 

showed prolonged shock, but by the 

end of the experiment were moving 

about vigorously. A salinity of 16.9 

ppt produced an initial shock but 

1 arvae recovered quickly (within 2 

h). Juveniles exposed to a salinity 

of 21 ppt acted normally. These 

studies i ndi cate that scal 1 op 1 arvae 

are somewhat euryhaline and may be 

able to survive in some estuaries. 
LITERATURE CITED 

Bai rd, F.T., Jr. 1953. Observations 

on the early life history of the 

giant scal fop (Pecten magel lanicus). Maine D~D. Sea Shore Fish. 

Baird, F.T., Jr. 1954. Migration of 

the deep sea scallop (Pecten 

magel lanicus ). Maine Dep. Sea Shore 

Fish., Fish. Circ. 14. 8 pp. 

Bourne, N. 1964. Scallops and the 

offshore fishery of the Maritimes. 

Fish. Res. Board Can. B1111. 145. 60 

PP 

Caddy, J.F. 1968. Underwater observations on scallop (Placopecten 

magel lanicus) behavior and drag 

efficiency. J. Fish. Res. Board Can. 

25: 2123-2141. 

Caddy, J.F. 1971. Recent scallop 

recruitment and apparent reduction 

in cell size by the Canadian fleet 

on Georges Bank. Int. Comm. 

Northwest At 1. Fish. Redbook, Part 

I1 I: 147-155. 

Caddy, J .F. 1973. Underwater observations on tracks of dredges and 

trawls and some effects of dredging 

on a scallop ground. J. Fish. Res. 

Board Can. 30: 173-180. 

Caddy, J .F. 1979. Long-term trends 

and evidence for production cycles 

in the Bay of Fundy scallop fishery. 

Rapp. P.-V. Reun. Cons. Int. Explor. 

Mer 175: 97-108. 

Cull i ney , J .L. 1974. Larval devel opment of the giant scallop 

Placo ecten ma ellanicus. Biol. 

hs Hob-332. 

Dickie, L.M. 1955. Fluctuations in 

a bundance of the giant scall op, 

Placopecten magel lanicus (~mel in), 

in the Diqby area of the Bay of 

Fundy. J. -~;sh. Res. Board -can. 

12: 797-857. 

Dickie, L.M. 1958. Effects of high 

temperatures on survival of the 

giant scallop. J. Fish. Res. Board 

Can. 15: 1189-1211. 

Dickie, L.M., and J.C. Medcof. 1963. 

Causes of mass mortalities of 

s c a l l o p s (Placopecten magel lanicus ) 

in the southwestern Gulf of St. 

Lawrence. J. Fish. Res. Board Can. 

20: 451 -482. 

Dow, R.L. 1969. Sea scallop fishery. 

Pages 616-623 i~ F.E. Firth, ed. 

The encyclopedia of marine 

resources. Van Nost rand Reinhol d 

Co., New York. 

Dow, R.L. 1971. Periodicity of sea 

scallop abundance fluctuations in 

the northern Gulf of Maine. 

Reprinted from Natl. Fisherman. Res. 

Bull. 31. Maine Dep. of Sea and 

Shore Fisheries. 

Elner, R.W., and G.S. Jamieson. 1979. 

Predation of sea scallops 

Pl acopecten magel 1 ani cus by the rock 

crab Cancer irroratus and the 

American lobster Homarus americanus. 

J. Fish. Res. Board Can. 36:537-543. 
Garman, G.C. 1983. Observations on 

juvenile red hake associated with 

sea scallops in Frenchman Bay, 

Maine. Trans. Am. Fish. Soc. 

112(2A): 212-215. 

Goode, C.B. 1884. Natural history of 

useful aquatic animals. Pages 

163-684 in The fisheries and fishery 

industries of the United States. 

U.S. Comm. of Fish and Fisheries, 

Washington, D .C . Jamieson, G.S., H. Stone, and M. 

Etter. 1982. Predation -. ~ of sea ~ - 

scallops, Plactopecten magel lanicus. 

by 1 ohsters Homarus americanus, and 

rock crabs, Cancer irroratus, in 

underwater caae enclosures . Can. J . Fish. Aquat. fci . 39: 499-505. 

Larsen, P.F., and R.M: Lee. 1978. 

Observations on the abundance, 

distribution and growth of 

post1 arval sea scall op. Pl acopecten 

magel 1 ani cus . on Georges Bank. 

Nautilus 92:112-116. 

MacKenzie, C.L., Jr. 1979. Biological 

and fisheries data on sea scallop 

Placopecten magel lani cus (Gmel in). 

NOAA Fish. Cent., Sandy Hook Lab., 

New Jersey. Tech. Ser. Rep. 19. 34 

PP 

MacKenzie, C.L., Jr., A.S. Merrill, 

and F.M. Serchuk. 1978. Sea scallop 

resources off the northwestern U.S. 

coast. Mar. Fish. Rev. 40:19-23. 

Medcof, J .C ., and N. Bourne. 1964. 

Causes of mortality of the sea 

scallop, Placopecten magel lanicus. 

Proc. Natl. Shellfish Assoc. 

Merri 11 , A.S. 1961. She1 1 morphology 

in the larval and post-larval stages 

of the' sea scallop, Placopecten 

magel lanicus (Gmel in). Bull. Mus. 

Comp. Zool . Harv. Univ. 125(1):1-20. 

Merrill, A.S., and J.B. Burch. 1960. 

Hermaphroditism in the sea scallop 

Pl acopecten magel lani cus (Gmel i n) . 

Biol . Rull . (Woods Hole) 

119: 197-201. 

Merrill, A.S., and R.L. Edwards. 1976. 

Observations on mollusks from a 

navigation buoy with special 

emphasis on the sea scallop, 

& Placo ecten magel lanicus . Nautilus 

Merrill, A.S., and Posgay, J.A. 1964. 

Estimating the natural mortality 

rate of the sea scallop (Placopecten 

rnagel lanicus). Int. Corn. Northwest 

Atl. Fish. Res. Bull. 1:88-106. 

Merrill, A.S., Posgay, J.A., and F.E. 

Nichy. 1966. Annual marks on the 

shell and liqament of sea scalloo, 

Placopecten iagellanicus. U.S. ~ish 

Wildl. Serv. Fish. Bull. 65:299-311. 

Naidu, K.S. 1969. Growth, reproduction, and unicellular endosymhiotic 

alga in the giant scallop, 

Placopecten magellanicus (Gmelin), 

in Port au Port Bay, Newfoundland. 

M.S. Thesis. Memorial University, 

Newf ou ndl and. 

Naidu, K.S. 1970. Reproduction and 

breeding of the giant scal lop, 

Pl acopecten magel 1 ani cus , in 

Port-au-Port Bay, Newfoundland. 

Can. J. Zool . 48: 103-1012. 

Porter, H.J. 1974. The North Carolina 

marine and estuarine mollusca - an 

atlas of occurrence. University of 

North Carolina, Inst. of Mar. Sci., 

Morehead City. 351 pp. 

Posgay, J .A. 1950. Investigations of 

the scal 1 op, Pecten grandis. Pages 

24-30 in Third report on investigations f methods of improving the 

she1 lfish resources of Massachusetts. Div. Mar. Fish., Dep. 

Conserv., Commonwealth of 

Massachsetts, Boston. 

Pos gay, J .A. 1953. Sea scallop 

investigations. Pages 9-24 - in Sixth 

report in investigations of the 

shellfisheries of Massachusetts. 
Div. Mar. Fish., Dep. Conserv., 

Commonwealth of Massachusetts, 

Boston. 

Posgay, J.A. 1957. The range of the 

sea scallop. Nautilus 71:55-57. 

Posgay, J.A. 1962. Maximum yield per 

recruit of sea scallops. Int. Comm. 

Northwest At1 . Fish. Res. Doc. 

62/73. Ser. 1616. 20 pp. 

Posgay, J.A. 1968. Trends in the 

Atlantic sea scallop fishery. 

Comer. Fish. Rev. 30: 24-26. 

Posgay, J.A. 1979. Popu 1 at i on 

assessment of the Georges Bank sea 

scallop stocks. Rapp. P.-V. Reun. 

Cons. Int. Explor. Mer 175: 109-113. 

Posgay, J.A. 1981. Movement of tagged 

sea scallops on Georges Bank. Mar. 

Fish. Rev. 43(4):19-25. 

Posgay, J.A. 1982. Sea scallop 

~laco~ecten magellanicus in fish 

distribution. MESA N.Y. Riqht - Atlas 

Monogr. 15. 

Posgay, J.A., and K.D. Norman. 1958. 

An observation on the spawning of 

the sea scallop, Placo ecten 

magel 1 ani cus (Gmel in) , & 

Bank. Limn01 . Oceanog. 3:478. 

Serchuk, F.M., P.M. Wood, J.A. Posgay, 

and B.E. Brown. 1969. Assessment 

and status of sea scallop (Placopecten magel lanicus) populations off 

the northeast coast of the United 

States. Proc. Natl. Shellfish. 

Assoc> 69: 161-191. 

Smith, H.M. 1891. The giant scallop 

fishery of Maine. Bull. U.S. Fish. 

Comm. 4: 313-335. 

Sutcliffe, W.H., Jr., K. Drinkwater, 

and B.S. Muir. 1977. Correlations of 

fish catch and environmental factors 

in the Gulf of Maine. J. Fish. Res. 

Board Can. 34(1): 19-30. 

Thompson, B.G. 1983. Fisheries of the 

United States, 1982. U.S. Natl. Mar. 

Fish. Serv. Curr. Fish. Stat. 8300. 

118 pp., and previous editions: 1981 

(Curr. Fish. Stat. 8200), 132 pp.; 

1980 (SlOO), 132 pp. ; 1979 (8ooo), 131 pp. 

Walton, C.J. 1979. Characterization 

of the she1 lfisheries. Pages 

326-258 in Fisheries management and 

development. Vol . 3, Element 0 

Completion Rep., 1978-1979. Maine 

Dep. Mar. Resour., W. Boothbay 

Harbor. 

Wigley, R.L., and R.B. Theroux. 

1971. Association between 

post-juvenile red lake and sea 

scal lops. Proc. Natl . She1 1 fish. 

Assoc. 61: 86-87. 
7. Author(.) 

Dennis M. Flu1 len and John R. Morii~g 

9. hdorming Orgbnir8tion Uanw and Addnsm 

Maine Cooperative Fish and Wild1 ife Research Unit 

Department of Zoo1 ogy 

313 Murray Hal 1 

University of Maine, Orono, Maine 04469 

12. Smn.onn# Or#anlxatlon Name and Addmm 

National Wetlands Research Center U.S. Army Corps of Engineers 

Fish and Wildlife Service Waterways Experiment Station 

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

Washington, D.C. 20240 Vicksburg, MS 39180 

SOIT? -101 

1 L ?*dormms Organ~ratlon hot. No. I 

1 

10. ?roiMITashWor(l Unlt Uo. 

S. I)u~p*nt'm kc*sl8on No. 

S. new- 0.1. 

, 1986 

L 

1 

IS. supple manta^ Notam 

*U.S. Army Corps of Engineers Report No. TR EL-84-4 

16 btm (Urn~t: 200 words) 

Species profiles are literature summaries of taxonomy, life 

history, and environmental requirements of coastal fishes and aquatic invertebrates. They are prepared to assist with impact assessment. The sea scallop, 

Placopecten magel lanicus, is a commercially important she1 1 fish found from 

North Carolina to the Gulf of St. Lawrence in intertidal to deep waters. 

Scallops spawn at age 1 from July to October, releasing up to one million 

eggs each year. Up to 8 cm in size, scallops are active in response to 

disturbances, but those over 9 cm in size do not move. The U.S. commercial 

fishery has been active for over 100 years, and landings in 1982 were 

9,700 t, valued at $78 mi 1 lion. Over 75% of the commercial landings of a1 1 

scallops occur in New England, principally in Massachusetts. Scallops are 

collected by commercial dredges and scuba divers. A wide variety of animals 

prey on scallops, and predation by several species of fishes may increase 

fol lowing injuries caused by commercial dredges. 

t REPORT DOCUMENTATION 1. ~0- 

17. Doarmmnt Anbly8m a. Oeunpton 

Shellfish 

Growth Temperature 

Fisheries Feeding habits 

Sal i ni ty Life cycles Sea scallop 

L Id~ntlh~nlCU~en-Ended Term% 

Sea Scallop 

Pl actopecten magell anicus 

Habitat requirements 

I 

I. ntl. and s~tt~. 

Species Profiles: Life Histories and Environmental Requirements of 

Coastal Fishes and Invertebrates (North Atlantic)--Sea Scallop 

PAGE Biological Report 82(11.67)* 

r tOSATI FieldlCmu~ 

19. Security Class CThsr Retmn) 

Unlimited distribution Unclassified 20. %curtly Class CThls Pa#*) 

21. No. of Pa.** 

13 -- +2. ?nu 

Qr ANSI-239.18l OPTIONAL FORM 272 (4-7'1) 

(Formrlr N715-3% 
TAKE PRIDE 

in Amerzcd 

DEPARTMENT OF THE IWTERIOR 

U.S. FISH AND WllDLlA SERVICE 

As the Nation's principal conservation agency. the Department of the Interior has responsibility for most of our .nationally owned public lands and natural resources. This includes 

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

preserving thsenvironmental and cultural values of our national parks and historical places, 

and providing for the enjoyment of life through outdoor recreation. The Department assesses our energy and mineral resources and works to assure that their development is in 

the best interests of all our people. The Department also has a major responsibility for 

American Indian reservation communities and for paople who live in island territories under 

U.S. administration.