(DRAFT) - Taxonomy
Species scallop, sea
Species Id M060006
Date 26 AUG 96

TAXONOMY

NAME - scallop, sea

OTHER COMMON NAMES - sea scallop

ELEMENT CODE -

CATEGORY - Aquatic Molluscs

PHYLUM AND SUBPHYLUM - Mollusca,

CLASS AND SUBCLASS - Bivalvia,

ORDER AND SUBORDER - Ostreoida,

FAMILY AND SUBFAMILY - Pectinidae,

GENUS AND SUBGENUS - Placopecten,

SPECIES AND SSP - magellanicus,

SCIENTIFIC NAME - Placopecten magellanicus

AUTHORITY - Gmelin, 1791

TAXONOMY REFERENCES - 186

COMMENTS ON TAXONOMY -
Other common names...Atlantic deep sea scallop, giant scallop, ocean
scallop, smooth scallop.*34*

Taxonomy - 1 (DRAFT) - Status
Species scallop, sea
Species Id M060006
Date 26 AUG 96

STATUS

Coded Status
Commercial
Commercial/consumption

REFERENCES FOR STATUS - 34

COMMENTS ON STATUS -
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
million were landed in the United States. North of Cape Cod, sea scallops
are highly valued by scuba divers.*34*

Status - 1 (DRAFT) - Distribution
Species scallop, sea
Species Id M060006
Date 26 AUG 96

DISTRIBUTION

Distribution - 1 HABITAT ASSOCIATIONS

NATIONAL WETLAND INVENTORY CODES

NWI NWICLS NWIMOD NWISPEC

Marine RB.
Marine OW0
Marine FL2

REFERENCES FOR NWI - 34

Habitat Associations - 1 (DRAFT) - Food Habits
Species scallop, sea
Species Id M060006
Date 26 AUG 96

FOOD HABITS

TROPHIC LEVEL -
FILTERER

REFERENCES FOR TROPHIC LEVEL - 34 and 157

LIFESTAGE FOOD FOOD PART
Larva Protozoans Not Specified
Adult Bacillariophyceae Not Specified
Adult Detritus - Organic Not Specified
Adult Crustaceans Larva stage
General See Comments; Food

REFERENCES FOR GENERAL FOOD - 34 and 157

REFERENCES FOR ADULT FOOD - 34 and 157

REFERENCES FOR LARVAE FOOD - 34 and 157

COMMENTS ON FOOD -
Like most bivavles, sea scallops are filter feeders, but there are few
published reports that identify preferential feed organisms. Specific items
that have been observed include microscopic plants (e.g., diatoms) and
animals (e.g., peridinians, tintinnids, ciliate protozoa), as well as
fragments of larger plants and planktonic stages of crustaceans. From these
observations, it is reasonable to conclude that sea scallops are primary
consumers that characteristically obtain their energy requirements
principally from the phytoplankton.*157*

COMMENTS ON ADULT FOOD -
Adult scallops are filter feeders, feeding on plankton and organic detritus.
Adults have been kept alive on a diet of the diatom Phaeodactylum
tricornutum.*34*

COMMENTS ON LARVAE FOOD -
Larval scallops were raised on a diet of the phytoplankter, Isochrysis
galbana, at concentrations ranging from 5,000 to 50,000 cells/ml. Spat were
raised on a mixture of I. galbana and Chrosomonas salina at a concentration
of about 10,000 cells/ml.*34*

Food Habits - 1 (DRAFT) - Environment Associations
Species scallop, sea
Species Id M060006
Date 26 AUG 96

ENVIRONMENTAL ASSOCIATIONS

G = General A = Adult
LIM = Limiting RA = Resting Adult
J = Juvenile FA = Feeding Adult
RJ = Resting Juvenile BA = Breeding Adult
FJ = Feeding Juvenile P = Pupae
L = Larvae E = Egg
RL = Resting Larvae
FL = Feeding Larvae

LIFESTAGE ENVIRONMENTAL ASSOCIATIONS
L Water Temperature: Specified in Comments
L Currents: specified in comments
L Relation to Substrate: Occurs on substrate [not penetrating]
L Bottom Type [Aquatic]: Rubble
L Bottom Type [Aquatic]: Boulders
L Bottom Type [Aquatic]: Bedrock
L Bottom Type [Aquatic]: Organic debris
L Substrate: Animals
L Stability of Bottom: Stable
A Bottom Type [Aquatic]: Sand
A Relation to Substrate: Unattached - normally free living
A Currents: specified in comments

REFERENCES FOR ENVIRONMENTAL ASSOC_ - 34

REFERENCES FOR RESTING JUVENILE ENVIRONMENTAL ASSOC_ - 34

REFERENCES FOR RESTING LARVAE ENVIRONMENTAL ASSOC_ - 34

COMMENTS ON ENVIRONMENTAL ASSOCIATIONS -
Sea scallops usually inhabit waters with salinities characteristic of
oceanic waters. Salinity tolerances of adult sea scallops have not been
studied, but the effects of different salinities on scallop larvae by
moving larvae from sea water into water of test salinities has been
studied.
While swimming, scallops may be carried long distances by currents.
Currents may be a means of migration for smaller scallops.*34*

COMMENTS ON RESTING ADULT ENVIRONMENTAL ASSOC_ -
Large scallops are recessed in the sediment and do not usually move unless
physically disturbed.*34* The high lethal temperature for adult sea
scallops ranges from 20 to 24 degrees C depending on the acclimation
temperature. The 20 degree C isotherm largely determines the southern
distribution of sea scallops. A sudden rise in water temperture over
scallop beds can induce mass mortality. The optimum temperature for growth
of adult sea scallops is 10 degrees C. Growth rates drop 5% at 8 degrees C
and 20% at 12 degrees C.*34*

Environment Associations - 1 (DRAFT) - Environment Associations
Species scallop, sea
Species Id M060006
Date 26 AUG 96

COMMENTS ON BREEDING ADULT ENVIRONMENTAL ASSOC_ -
Sea scallops spawn at temperatures between 14 and 16 degrees C in New
Hampshire, and between 10 and 15 degrees C in the laboratory. Scallops
spawn in Newfoundland at temperatures between 4.2 and 16.1 degrees C.
Spawning may be triggered by a rapid drop in temperature in the fall*34*.

COMMENTS ON FEEDING JUVENILE ENVIRONMENTAL ASSOC_ -
Larvae raised under laboratory conditions grew well at a temperature of 15
degrees C but few survived at 19 degrees C.*34*. Juveniles exposed to a
salinity of 21 ppt acted normally. These studies indicate that scallop
larvae are somewhat euryhaline and may be able to survive in some
estuaries.*34*

COMMENTS ON RESTING LARVAE ENVIRONMENTAL ASSOC_ -
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 larvae recovered quickly (within
2 h).*34*

Environment Associations - 2 (DRAFT) - Life History
Species scallop, sea
Species Id M060006
Date 26 AUG 96

LIFE HISTORY

PHYSICAL DESCRIPTION:

Adult. The shell 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 shells.) 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
lamellae or growth lines. 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 pallial scars (roughened areas may
be present due to secretions laid down to repair damage from boring
organisms). The adductor muscle scar is located slightly posterior and
dorsal to the center of the valves and is slightly larger on the left
valve.*34*

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 lines are lacking on the right valve. The adductor muscle
scar is well off center.*34*

REPRODUCTION:

Sea scallops in Port au Port Bay, Newfoundland, reach sexual maturity and
spawn for the first time at age 1, just after the formation of the first
growth ring. Sexes are usually separate. Examples of exceptions are two
hermaphrodites among about 3,000 scallops examined from Georges
Bank water and 42 of about 3,000 examined from Port au Port Bay,
Newfoundland. 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.*34*

Spawning season occurs later as one moves from south to north and has been
reported as July along North Carolina and Virginia coasts, as late July to
mid-August offshore on the shelf, as late September near the Isles of
Shoals, New Hampshire, and late September or early October in the Georges
Bank area. 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. The temperature during spawning also varies
among location. In 1966, scallops spawned in Port au Port Bay as
temperatures fell from 16.1 to 4.2 degrees C. In 1973, scallops spawned
when the water temperature was 14 degrees C in the Isles of Shoals waters,
and 10 degrees C in the laboratory. In 1975, spawning temperatures ranged
from 9 to 11.2 degrees C in Georges Bank waters and from 6.5 to 11 degrees C
in Middle Atlantic shelf waters. The duration of the spawning season has
Life History - 1 (DRAFT) - Life History
Species scallop, sea
Species Id M060006
Date 26 AUG 96

been reported to be as short as 1 week in Georges waters and as long as 5
weeks in Port au Port Bay.*34*

BEHAVIOR:

Scallop larvae remain planktonic for over a month after hatching. The first
spatfall of laboratory-spawned larvae was 35 days after hatching.
Planktonic scallop larvae in the sea may be transported out of the spawning
area by predominant currents. Based on this observation it was postulated
that none of the large North Atlantic scallop populations (with the
exception of 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 laboratory,
pediveligers develop a thick strong byssus and crawl around extensively in
search of a hard surface for attachment. The spat attach themselves to the
underside of shell fragments and other solid materials on the bottom. This
behavior may protect the spat from epibenthic predators, such as crabs.
Once attached, the pediveligers begin metamorphosis into the adult form.
The larvae are able to delay metamorphosis for up to 1 month while searching
for appropriate substrate.*34*

Because scallop spat attach to navigation buoys located only in areas of the
buoys that were free of other mollucks, it was concluded that scallops do
not compete well with the other mollusks for food or space. Young scallops
frequently settle on the bryzoan, Gemelleria. It is believed that sea
scallops prefer shell fragments and other animals for setting because young
scallops are unable to survive on shifting sand bottoms.*34*

Young adults larger than 10 mm long detach from the epibenthic substrate and
settle on the bottom. Scallops are relatively active until they are about 8
cm long, swimming in response to disturbances such as predation and
commercial dredging.*34*

Scallops swim by rapidly closing the valves and forcing water through ports situated on the wings. Swimming scallops move
situated on the wings. Swimming scallops move through the water with the
hinge aft. Each contraction moves the scallop about 125 cm. Some move
at ground speed of 67 cm/sec for distances up to 4 m, and, while swimming,
scallops may be carried long distances by currents. Currents may be a means
of migration for smaller scallops.*34*

Large adult scallops ( > 9 cm long) do not migrate. Large scallops are
recessed in the sediment and do not usually move unless physically
disturbed.*34*

LIMITING FACTORS:

Predation. A list of known predators of larval sea scallops includes a wide
Life History - 2 (DRAFT) - Life History
Species scallop, sea
Species Id M060006
Date 26 AUG 96

variety of planktivores. The major natural predators of juvenile and adult
scallops are us follows: rock crab, Cancer irroratus, lobster, Homarus
americanus, starfish, Asterias vulgaris, and Crossaster papposus, moonsnail,
Lunatia heros, a burrowing anemone, Ceriantheopsis americanus, Atlantic cod,
Gadus morhua, American plaice, Hippoglossoides platessoides, and Atlantic
wolffish, Anarhicas lupus.

Studies show that scallops that had been injured by commercial drag
operations are preyed upon by several species of ground fish, e.g. the
sculpins, Myoxocephalus sp., and the winter flounder, Pseudopleuronectes
americanus. Laboratory studies show that juvenile lobsters prey on scallops
larger than themselves, and that prey size tends to increase with the size
of the predator. Because of the large size of adult scallops, rock crabs
and lobsters feed more on the smaller, more abundant juvenile scallops.*34*

Temperature. The high lethal temperature for adult sea scallops ranges from
20 to 24 degrees C, depending on the acclimation temperature. The 20
degrees C isotherm largely determines the southern distribution of sea
scallops. A sudden rise in water temperature over scallop beds can induce
mass mortality.*34*

POPULATION ATTRIBUTES:

Growth Characteristics. The age and growth rate of scallops are calculated
by reading annual rings formed on the shell in early spring, or empirically
by tagging, releasing, and recapturing live scallops. 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. Growth in
the first several years is rapid. Between the 3rd and 5th years of life,
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
meat per scallop in the waters of Georges Bank and the Mid-Atlantic shelf.
After age 8, the annual growth increment falls to less than 10% per
year.*34*

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 and by calculating juvenile densities on
navigation buoys. Samples of spatfalls from the Nantucket Shoals lightship
buoy revealed a juvenile scallop density of 392/m(squared). Scallops ranged
in height from 0.5 mm (just settled) to 13.2 mm (about one year old). 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/m(squared). In May, the
density was about 2 to 63 spat/m(squared).

In 1960, the density of adult scallops was about 1 per square meter for the
274 km(squared) northern edge of Georges Bank. The population estimate was
about 270 million. Scallop density varies with substrate. In 1967, in the
Northumberland Strait of the Gulf of St. Lawrence, estimated densities were
4.2 adult scallops/m(squared) on sandy bottoms and 1.4/m(squared) on mud
bottoms.
Life History - 3 (DRAFT) - Life History
Species scallop, sea
Species Id M060006
Date 26 AUG 96

An equation for estimating the natural mortality of the sea scallop was
developed based on the observation that the two valves (clappers) of dead
scallops remain attached for a known period. Natural mortality is computed
by the equation:
M = (C/L) (52/t)

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 remain attached.*34*

The Fishery. Scallops reach a commercially attractive size in their fifth
or sixth year of life when they comprise over 90% of the landings. 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.

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 1982, landed
4,312.4 metric tons. 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.

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.

Scallops are usually fished with dredges. Dredge size and type varies with
locality. Scallop dredges operated from vessels in Georges Bank and
Mid-Atlantic Shelf waters are about 3-4 m wide. 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. Dredges are more efficient
in capturing the large, less active scallops and less efficient in capturing
the smaller, more active scallops.

In rocky nearshore areas, scuba divers gather scallops commercially. The
catch is sold to 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.*34*

REFERENCES FOR LIFE HISTORY- 34

Life History - 4 (DRAFT) - Management Practices
Species scallop, sea
Species Id M060006
Date 26 AUG 96

MANAGEMENT PRACTICES

RESULT MANAGEMENT PRACTICE

Existing Regulating harvest of species being described
Existing Regulating harvest - setting seasons
Existing Regulating harvest - setting size limits
Beneficial Regulating harvest of species being described
Beneficial Regulating commercial harvest levels
Beneficial Regulating harvest - setting seasons
Beneficial Regulating commercial harvest gear types
Beneficial Restricting/regulating human use of habitats

REFERENCES FOR BENEFICIAL MANAGEMENT PRACTICES - 157

REFERENCES FOR EXISTING MANAGEMENT PRACTICES - 157

COMMENTS ON MANAGEMENT PRACTICES -
The State of Maine requires a license for commercial harvesting of sea
scallops from its waters. License eligibility is limited to Maine
residents. No quota is imposed on the commercial fishery, but only sea
scallops with a shell height of 3 or more inches (7.6 cm) may be landed or
possessed. Regulations specify areas where harvesting by dredge and by
otter trawl is authorized, and the sea scallop season is limited to
November 1 through April 15 in coastal waters. Recreational sea scallop
fishing in Maine does not require a license, but individual fishermen are
limited to two bushels of scallops in the shell or four quarts of shucked
scallops per day. Scallops retained by recreational fishermen must meet the 3 inch minimum
shell height. The state law permits a 10% tolerance under the minimum
size.*157*

Massachusetts and New Hampshire also have sea scallop landing laws setting a
3 inch minimum shell size. In mid-1980, North Carolina fisheries
authorities and advisors were considering restictions on shell size and meat
count. No state regulations currently exist for sea scallops in New Jersey,
New York, Rhode Island, Connecticut, Virginia, or North Carolina.*157*

Management Practices - 1 (DRAFT) - References
Species scallop, sea
Species Id M060006
Date 26 AUG 96

References

34* Mullen, D., J. Moring. 1986. Species Profiles: Life Histories
and Environmental Requirements of Coastal Fishes and
Invertebrates (North Atlantic) -- Sea Scallop. U.S. Fish and
Wildlife Service Biol. Rep. 82(11.67) pp 13.

157* New England Fishery Mangement Council. 1982. Fishery Management
Plan Final Environmental Impact Statement Regulatory Impact
Review for Atlantic Sea Scallops (Placopecten magellanicus).
U.S. Fish and Wildlife Service Biol. Rep. pp 149.

186 * Turgeon, D.D., A.E. Bogan, E.V. Coan, W.K. Emerson, W.G.
Lyons, W.L. Pratt, C.F.E. Roper, A. Scheltema, F.G. Thompson,
J.D. Williams. 1988. Common and scientific names of aquatic
invertebrates from the United States and Canada: mollusks.

References - 1