(DRAFT) - Taxonomy
Species scallop, bay
Species Id M060150
Date 26 AUG 96
TAXONOMY
NAME - scallop, bay
OTHER COMMON NAMES - bay 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 - Argopecten,
SPECIES AND SSP - irradians,
SCIENTIFIC NAME - Argopecten irradians
AUTHORITY - Lamarck, 1819
TAXONOMY REFERENCES - 186
COMMENTS ON TAXONOMY -
Three subspecies of Argopecten irradians are generally recognized,
intergrading in distribution, with A. i. irradians extending from Cape Cod
to New Jersey, A. i. concentricus from New Jersey to the Chandeluer Islands
in the Gulf of Mexico, and A. i. amplicostatus from Galveston, Texas, to
Laguna Madre, Texas (Waller 1969).*54*
Taxonomy - 1 (DRAFT) - Status
Species scallop, bay
Species Id M060150
Date 26 AUG 96
STATUS
Coded Status
Commercial
Commercial/consumption
See Comments
REFERENCES FOR STATUS - 54
COMMENTS ON STATUS -
Bay scallops have been harvested since colonial 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). In 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).*54*
Status - 1 (DRAFT) - Distribution
Species scallop, bay
Species Id M060150
Date 26 AUG 96
DISTRIBUTION
Distribution - 1 HABITAT ASSOCIATIONS
Habitat Associations - 1 (DRAFT) - Food Habits
Species scallop, bay
Species Id M060150
Date 26 AUG 96
FOOD HABITS
TROPHIC LEVEL -
FILTERER
REFERENCES FOR TROPHIC LEVEL - 54
LIFESTAGE FOOD FOOD PART
Adult Microorganisms
Adult Bacteria
Adult Cyanophyta
Adult Protozoans
REFERENCES FOR ADULT FOOD - 54
COMMENTS ON FOOD -
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.
Normal feeding position of adults is resting on the bottom on the right
valve, with a shell gape of approximately 20 degrees (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
FOOD HABITS: Investigations 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.
In the laboratory, larval bay scallops were successfully reared on
suspensions of either green algae (Chlorells spp.), or a combination of
naked flagellates (Isochrysis galbana and Monochrysis lutheri). Growth was
better on the flagellate diet. Both larval and adult bay scallops were
reared and maintained successfully on either flagellates (M. lutheri and
Dunaliella tertiolecta) or diatoms (Phaeodactylum tricornutum).
sand and the left valve exposed to the water (Belding 1910).*54*
Food Habits - 1 (DRAFT) - Environment Associations
Species scallop, bay
Species Id M060150
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
E Water Temperature: Between 21-27 degrees C
A Air Temperature: Specified in Comments
A Flow: Less than 5 cfs mean annual flow
G
L
E
REFERENCES FOR ENVIRONMENTAL ASSOC_ - 54
COMMENTS ON ENVIRONMENTAL ASSOCIATIONS -
Temperature
Castagna (1975) reported that survival and development of eggs were best
at water temperatures above 20 degrees C. Optimum temperatures for
development appeared to be 26 degrees to 28 degrees C. Belding (1910)
stated that Massachusetts by scallops need a temperature over 7.2 degrees C
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 -6.6 degrees C for 2 hours. 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,
166, 1968, 1970a, 1970b), and by Sastry and Blake (1971) on relationships
between temperature, food, gonad development, and spawning. Overwintering
scallops in a "resting reproductive state" could not survive direct
exposure to 25 or 30 degrees C. They survived at 25 degrees C if an
acclimation period of 30 days at 15 or 20 degrees C and adequate food were
provided. Gametogenesis was stimulated in all overwintering scallops held
at 15 and 20 degrees C, with or without food; but the most advanced stage
of gametogenesis (dissolution of germinal vessicle) was achieved only by
scallops held at 20 degrees C with adequate food. After dissolution of the
germinal vesicle, temperatures greater than 20 degrees 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, 25, or 30
degrees C, even without food. Spring-collected scallops held at 10 and 15
degrees C 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
Environment Associations - 1 (DRAFT) - Environment Associations
Species scallop, bay
Species Id M060150
Date 26 AUG 96
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 salinity 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 10 to
15 degrees C, all experimental animals showed "reduced activity" as
salinity reached 22 ppt, and "no activity" when 16 ppt was reached. At 20
to 25 degrees C, "reduced activity" when 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.*54*
Water Currents
Water currents seem to influence food availability, waste removal,
growth rate, larval movements, and distribution of juvenile
settlements.*54*
Environment Associations - 2 (DRAFT) - Environment Associations
Species scallop, bay
Species Id M060150
Date 26 AUG 96
COMMENTS ON RESTING LARVAE ENVIRONMENTAL ASSOC_ -
Bay scallop larvae could not tolerate 10-ppt salinity or 35 degrees C; at
least some larvae survived at all other test temperatures and salinities.
Maximum larval survival occurred at 20 degrees C and 25 ppt salinity.*54*
COMMENTS ON FEEDING LARVAE ENVIRONMENTAL ASSOC_ -
Minimum requirements for larval growth were 25 to 30 degrees C and
20-35-ppt salinity. Larval growth was maximized at 25 degrees C and 25 ppt
salinity (Tettelbach and Rhodes 1981). Tettlebach and Rhodes also gave
multiple regression equations for predicting larval survival through 5
days, larval survival through 8 days (settlement), larval growth through
5 days, and larval growth through 8 days, from temperature and salinity of
the rearing environment.*54*
COMMENTS ON EGG ENVIRONMENTAL ASSOC_ -
Bay scallop embryos require a narrow range of temperature-salinity
combinations for proper development. The optimum combination for normal
development was reported at 20 to 25 degrees C (test temperatures at 5
degree C increments) and 25 ppt salinity. Salinities above or below 25 ppt
signigicantly affected normal embryonic development. No embryos developed
normally at 10 ppt salinity, or at water temperatures of 10 or 35 degrees C
(Tettelbach and Rhodes 1981).*54*
Environment Associations - 3 (DRAFT) - Life History
Species scallop, bay
Species Id M060150
Date 26 AUG 96
LIFE HISTORY
Morphology/Identification Aids
Distinguishing among the queen scallop (Chlamys opercularis), calico
scallop (Argopecten gibbus), and bay scallop is difficult without specimens
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 on 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.
REPRODUCTION PHYSIOLOGY/STRATEGY: Bay scallops are hermaphroditic and
generally protandrous (releasing male gametes before female gametes). A
single individual may release both types of gametes in a single spawning
period; but because of protandry, self-fertilization in nature is probably
rare. Bay scallops mature and spawn for the first time at approximately one
year of age. Although size at age one varies because of differences in
growth rates among populations, maturity is a function of age, not size.
Since the average longevity is only 12 to 16 months, and maximum longevity
about 26 months, few individuals spawn more than once.
SPAWNING: In the mid-Atlantic region, bay scallops spawn from mid-April
through early September. Specific spawning times, however, vary
considerably across the species range. In Massachusetts, Connecticut, Rhode
Island, and Long Island Sound, most spawning occurs during June and July,
when water temperatures increase. In contrast, populations in North
Carolina and Florida 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.
Gametogenesis and spawning time of bay scallops are correlated with water
temperature and food supply. A water temperature of at least 15 deg C was
necessary for initiation of gametogenesis in overwintering bay scallops,
while at least 20 deg C and adequate food supply were necessary for
gemetogenesis to reach the "germinal vesicle dissolution" stage. For
spring-collected scallops, maturation and spawning occurred with or without
food for scallops held at 20, 25, and 30 deg C, while those held at 10 and
15 deg C did not mature and spawn. Variation in reproductive physiology in
Life History - 1 (DRAFT) - Life History
Species scallop, bay
Species Id M060150
Date 26 AUG 96
geographically separated bay scallop populations (Woods Hole, Massachusetts,
compared to Beaufort, North Carolina) is probably an adaptive response to
differences in water temperature regime and timing of maximum available food
supply.
EGGS: Unfertilized bay scallop eggs average 60 millimicrons in diameter,
and range from 55 to 65 millimicrons. Eggs are often asymmetrical prior to
release into water, but rapidly become spherical or nearly so after release.
Yolk granules are numerous and small. Fertilization occurs in the water
column or on the bottom, and fertilized eggs are demersal. Egg development
accelerates as temperature increases; however, a critical thermal minimum
between 15 and 20 deg C was reported for successful early cleavages to
occur. Gastrulation occurred in 9 hr at 24 deg C; subsequent stages of
embryogenesis have been presented.
LARVAE: At 24 to 25 deg C, trochophore larvae first appeared from swimming
gastrulae after 24 hr, and all surviving eggs had developed into trochophore
larvae by 48 hr. 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 hr. Average size of veliger larvae reared at
24 deg C was 101 millimicrons. The veliger larvae began feeding activity by
using their ciliated velum. By the third day of the veliger stage, average
shell size was 122 millimicrons, and the straight-hinged veliger shell began
to develop curved umbones characteristic of the pediveliger stage. The
veliger stage lasted about 10 days; by this time the foot was fully
developed (pediveliger stage), and metamophosis to the juvenile stage
occurred. Average shell length of juveniles at settlement was 190
millimicrons, gills had developed, and the velum was completely absorbed.
Total time between egg fertilization and settlement is about 14 days, but
ranges from 10 to 19 days, depending not only on water temperature, but also
on food supply. Unfed larvae will not metamorphose.
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. 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. 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 in length, at
which time it drops to the bottom. Very young scallops (<10 mm or 0.4 in)
apparently cannot tolerate highly silted substrates; thus, attaching to
epibenthic surfaces until reaching 20 to 30 mm and then dropping to the
bottom probably improves their survival rate.
Juvenile bay scallops use a variety of substrates as settlement/attachment
locations, including stones, seaweeds, oyster shells, rope, and filamentous
algae. Beds of eelgrass and other seagrasses are apparently preferred as
settlement locations, though scallops are able to settle and survive in
areas lacking seagrasses. Young bay scallops grew faster in slow currents
compared to fast current; amd since seagrass beds tend to slow normal water
currents, 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 accidentally land on
Life History - 2 (DRAFT) - Life History
Species scallop, bay
Species Id M060150
Date 26 AUG 96
its left valve (characteristically, all bay scallops rest and feed on their
right valve).
Juvenile bay scallops tend to vary more in coloration than adults, and range
from nearly pure white to dark grey or brown, with some predominently red
individuals present. Lightly colored young scallops darken as they age,
while darker juveniles change little in color.
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. 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 law enforcement personnel to determine whether illegal (subadult)
scallops have been commercially harvested.
Even though adult scallops retain the ability to attach by byssal threads,
they are seldom found attached in nature. Adult scallops preferred quiet
waters, protected from high winds, storms, and tides. Preferred depths
range from 0.3 to 10 m, though occurrence to 18 m has been reported.
Scallops are often most abundant on tidal flats with only 0.3 to 0.6 m of
water at low tide.
Adult bay scallops are effective swimmers at all sizes. 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.
Voluntary movement of bay scallops is used to escape unfavorable
environmental conditions or predators. Using tagged scallops from the
Niantic River Estuary, Connecticut, it was found that summer movements of
bay scallops were 0.8 m 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. 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
has been noted, no such evidence for extensive migrations has been
presented.
The average life span of bay scallops ranges from 12 to 24 months in waters
south of Maryland, and from 20 to 26 months in waters north of Maryland.
Maximum reported life span was 26 months to 30 months for populations
north of Connecticut.
GROWTH CHARACTERISTICS: Growth rates of bay scallops seem to depend on
water temperature, current velocity, food availability, and possibly scallop
density. Growth rates in shell diameter reported in early literature
varied from 3.8 to 8.0 mm per month, with most of this growth occurring
during the 4 or 5 warmest months of the year. Growth of Massachusetts bay
scallops ranged from 3.8 to 4.5 mm per month over three years of study.
Growth rate was highest May, August, September, and October, and only about
half as fast in June and July, when these populations spawned. North
Carolina scallops may begin to grow as early as February, even though water
Life History - 3 (DRAFT) - Life History
Species scallop, bay
Species Id M060150
Date 26 AUG 96
temperatures may be as low as 3 deg C. Growth ceased after October, even
though water temperatures were still above 20 deg C. 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. Scallops
held at 27 deg C over 21 days showed no growth at a current velocity of 12.4
cm/s; those exposed 3 to 4 cm/s grew an average of 0.5 mm; exposure to 0.75
and 0.21 cm/s produced the highest growth rate of 4 mm (5.7 mm/month).
Scallop growth in standing water was not investigated. Phytoplankton
removal by scallops was most efficient at the lower current speeds, and this
may account for the observed growth patterns.
The optimum conbination of temperature and food particle density for growth
was 1.2 ug/l of chlorophyll a at 22 deg C. Growth was lower at higher
temperatures (e.g., 28 deg C), even with high food particle density (2.4
ug/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.
Bay scallops from Virginia waters held in cages at the surface, 1 m below
the surface, 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 over
the 5 months. Effects of scallop density on growth were also investigated.
Up to a size of 27 to 28 mm, growth was not significantly different at
scallop densities of 1075, 806, 537, and 269/m sqr; above this size, growth
decreased with increasing density. At termination of the experiment (4
months), average sized ranged from 40 mm at the highest density to 49 mm at
the lowest density.
Growth rates over 3 months, mean size at age, and mean weight at age were
consistantly lower for North Carolina bay scallops experimentally infected
with femane pea crabs (Pinnotheres maculatus, an internal, commensal
parasite of bay scallops), compared to uninfected scallops. Evidence
indicated that parasitism by the pea crab, though not directly fatal to the
scallop, affected the ability of bay scallops to grow.
The condition of bat scallops in relation to the environment in four
separate populations of the Niantic River, Connecticut, was investigated.
Environments of the four populations were generally similar except for tidal
current; two populations were in relatively current-free areas, and two
were in areas with strong tidal currents. The formula for calculating bay
scallop condition was:
K = V/L ^N
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 for all four populations combined, applicable to
scallops of age 7 to 20 months, was:
log(K) = 0.06197(t) - 0.06203
where t = time in months.
Life History - 4 (DRAFT) - Life History
Species scallop, bay
Species Id M060150
Date 26 AUG 96
FOOD HABITS: Investigations 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.
In the laboratory, larval bay scallops were successfully reared on
suspensions of either green algae (Chlorells spp.), or a combination of
naked flagellates (Isochrysis galbana and Monochrysis lutheri). Growth was
better on the flagellate diet. Both larval and adult bay scallops were
reared and maintained successfully on either flagellates (M. lutheri and
Dunaliella tertiolecta) or diatoms (Phaeodactylum tricornutum).
FEEDING BEHAVIOR: Bay scallops are filter-feeders, pumping water through
the mantle cavity and straining food particles on the gill cilia.
Observations 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 relationship can be described by F
= KW^b, where F = filtration rate, W = body weight, and K and b are
constants, a value of -0.58 was obtained for b. Filtration rates for
scallop size classes 38 to 44 mm, 47 to 48 mm, 54 to 56 mm, and 64 to 65 mm
were reported at 0.99, 0.93, 0.79, and 0.71 l/hr/g wet weight, respectively.
Normal feeding position of adults is resting on the bottom on the right
valve, with a shell gape of approximately 20 deg. Water movement through
the body is anterior to posterior. When the scallops occasionally lands on
its left valve, it quickly flips over using its foot and water expulsion.
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.
PREDATORS: In shallow water areas, where bay scallops are often abundant,
the most important predators are probably the green crab (Carcinides maenes)
and the blue crab (Callinectes sapidus). In water deeper than 2 m,
principal predators are the asteriod starfish Asterias spp. and
Marthasterias spp. Starfish attack the scallop by attaching tube feet to
both valves and pulling in opposite directions until the adductor muscles of
the scallop fatigue. Another predator is the oyster drill (Urosalpinx
cinerea). It was noted, however, 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), and the ability
of bat scallops to respond quickly to tactile stimuli and escape predators.
Lastly, the herring gull (Larus argentatus) 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.
COMPETITORS: No evidence is available on interspecific competition
involving bay scallops. There is some evidence of intra specific
competition. Density studies indicated that very high scallop densities (on
Life History - 5 (DRAFT) - Life History
Species scallop, bay
Species Id M060150
Date 26 AUG 96
the order of 1075/m sqr) decreased growth and increased mortality compared
to lower densities (269/m sqr). Even the lowest densities tested, however,
were considerably higher than densities in natural populations studied.
PARASITES: The pea crab is an internal commensal parasite of bay scallops,
and the gastropod Odostomia seminuda has been reported as an ectoparasite.
Bay scallops infected with pea crabs grew slower and were consistantly lower
in mean weight than uninfected scallops. Incidence of infection with pea
crabs ranged from 4% 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.
REFERENCES FOR LIFE HISTORY- 54
Life History - 6 (DRAFT) - Management Practices
Species scallop, bay
Species Id M060150
Date 26 AUG 96
MANAGEMENT PRACTICES
RESULT MANAGEMENT PRACTICE
Beneficial Mariculture activities
Beneficial Maintaining undisturbed/undeveloped areas
REFERENCES FOR BENEFICIAL MANAGEMENT PRACTICES - 54
REFERENCES FOR ADVERSE MANAGEMENT PRACTICES - 54
COMMENTS ON MANAGEMENT PRACTICES -
Distribution of the bay scallop 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.*54*
Aquaculture potential
Studies by Kirby-Smith, Kirby-Smith and Barber (1974), Castagna (1975),
and Epifaunio (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
aquaculture 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 (<2 degrees C)
ice-covered waters for a minimum of four months; (2) high number and
intensity of spring freshets, frequently reducing salinity below the minimum
requirement of 14 ppt; (3) limited 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.
*54*
Management Practices - 1 (DRAFT) - References
Species scallop, bay
Species Id M060150
Date 26 AUG 96
References
54* Fay, C., R. Neves, G. Pardue. 1983. Species Profiles: Life
Histories and Environmental Requirements of Coastal Fishes and
Invertebrates (Mid-Atlantic)--Bay Scallop. U.S. Fish and
Wildlife Service Biol. Rep. 82(11.12) pp 17.
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