(DRAFT) - Taxonomy
Species quahog, northern
Species Id M060130
Date 26 AUG 96
TAXONOMY
NAME - quahog, northern
OTHER COMMON NAMES - N. quahog and hard-shelled clam
ELEMENT CODE -
CATEGORY - Aquatic Molluscs
PHYLUM AND SUBPHYLUM - Mollusca,
CLASS AND SUBCLASS - Bivalvia,
ORDER AND SUBORDER - Veneroida,
FAMILY AND SUBFAMILY - Veneridae,
GENUS AND SUBGENUS - Mercenaria,
SPECIES AND SSP - mercenaria,
SCIENTIFIC NAME - Mercenaria mercenaria
AUTHORITY - Linnaeus, 1758
TAXONOMY REFERENCES - 186 and 177
COMMENTS ON TAXONOMY -
Other common names are quohaug, hard-shelled clam, round clam, cherrystone
clam, little-necked clam. *39* Widely known as Venus mercenaria before Wells
(1957) reassigned the species to the genus Linneaus orginally applied.*39*
Mercenaria comes from the shell's use in making Indian money or wampum.*177*
The name qauhog comes from the Narragansett Indian name "poquauhock" and has
an alternate spelling "quahaug". Still other names are based on a quahog's
size. Little necks (or "necks") are the smallest legal size, measuring 1
inch thick at the thickest part; chowders are the largest size; and
cherrystones are in between. Quahogs, like softshell clams, oysters,
scallops, and mussels, are classified as bivalve mollusks because they have
hinged shells made up of two halves or "valves". Like most bivalves,
quahogs obtain their food by "filter feeding." Water is taken in through a
tubelike siphon and passed over the gills which are specially adapted to
filter out food (microscopic algae and other small organic particles). The
filtered water is then expelled via another siphon. A large clam can filter
about a gallon of water in one hour.*279*
Taxonomy - 1 (DRAFT) - Status
Species quahog, northern
Species Id M060130
Date 26 AUG 96
STATUS
Coded Status
Commercial
Commercial/consumption
Game (Consumptive Recreational)
REFERENCES FOR STATUS - 57
COMMENTS ON STATUS -
Hard clams are the most extensively distributed commercial clam in the
United States and have the greatest total market value (Ritchie 1977).
Their abundance in clean substrates accessible to the public makes the hard
clam a popular recreational species. Their habitat is vulnerable to coastal
construction projects and pollution from urban and industrial development.
Because adults do not migrate, repopulation of over-fished hard clam beds
depends on the transport of larvae from other areas and several years for
growth, maturation, and reproduction. Any disturbance, however temporary,
may cause a long-term impact.*57*
Hard clams are prominent members of the benthic community in Chesapeake Bay
and contribute substantially to the economy of the region. Hard clams have
maintained more stability in population numbers, primarily due to greater
market demand for surf clams and ocean quahogs in the mid-Atlantic region
*136*.
Status - 1 (DRAFT) - Distribution
Species quahog, northern
Species Id M060130
Date 26 AUG 96
DISTRIBUTION
Distribution - 1 HABITAT ASSOCIATIONS
HABITAT - AQUATIC
REFERENCES FOR HABITAT - 39
NATIONAL WETLAND INVENTORY CODES
NWI NWICLS NWIMOD NWISPEC
Estuarine, intertidal FL2 V 3
REFERENCES FOR NWI - 57
COMMENTS ON HABITAT ASSOCIATIONS -
Hard clams tend to be found in protected locations within bays and
estuaries. The hard clam lives in the substrate and burrows with a
muscular foot. It remains in the location at which it first burrows for
the remainder of its life.*57*
ANIMAL/PLANT SPECIES ASSOCIATIONS -
fish
crabs
waterfowl
REFERENCES FOR SPECIES ASSOCIATIONS - 136
COMMENTS ON SPECIES ASSOCIATIONS -
Hard clams favor shallow burrows and are preyed upon by fish, crabs, and
waterfowl, particularly during the juvenile stage. Also of commercial
Habitat Associations - 1 (DRAFT) - Food Habits
Species quahog, northern
Species Id M060130
Date 26 AUG 96
FOOD HABITS
TROPHIC LEVEL -
FILTERER
REFERENCES FOR TROPHIC LEVEL - 57 and 136
LIFESTAGE FOOD FOOD PART
Adult Microorganisms Not Applicable
Adult Plankton Not Applicable
General Detritus Not Specified
General Phytoplankton Not Specified
General Bacteria Not Specified
General Zooplankton Not Specified
REFERENCES FOR GENERAL FOOD - 57 and 136
REFERENCES FOR ADULT FOOD - 57
COMMENTS ON FOOD -
Adult hard clams feed by filtering out plankton and micro-organisms that are
carried along the bottom by currents (Chesnut 1951). Hard clams depend on
plankton for food before and during spawning to furnish sufficient energy to
ripen the gonads (Ansell 1967). If the food supply is inadequate, spawning
is diminshed or nil. In the laboratory, food densities of 300 mg/l of
carbon are optimal for deposition of biomass (Tenore and Dunstan 1973).
Food and other materials are taken in by the clam through the incurrent
siphon. Tentacles on the siphon detect excessive concentrations of
oversized particles in the water and cause the siphon to close. The mantle,
visceral mass, and gills are ciliated and secrete mucus. Particles brought
in through the incurrent siphon attach to the mucus. Deposits on the gills
are collected by the cilia and carried towards the mouth (Kellogg 1903).
The palps at the mouth entrance determine, by volume, whether the particle
mass is ingested or rejected. Only small masses are selected for digestion.
Complex patterns off cilia movement remove the waste, called pseudofeces,
from palps and gills. Eventually all waste materials are collected on the
mantle and carried to the base of the siphon, avoiding the stream of
incoming seawater. When sufficient waste has been collected, the adductor
muscle suddenly contracts, forcibly ejecting a stream of water containing
the waste mass from the incurrent siphon (Kellogg 1903).*57*
Hard clams are important benthic species in the Bay. These clams are
infaunal suspension feeders, ingesting small detrital particles and
phytoplankton, as well as bacteria and microzooplankton in the case of Mya
spp. Hard clams favor shallow burrows and are preyed upon by fish, crabs,
and waterfowl, particularly during the juvenile stage. Also of commercial
importance the hard clam populations in the Bay suffer from irregular
recruitment and are striclty limited to higher salinity regions *136*.
Food Habits - 1 (DRAFT) - Environment Associations
Species quahog, northern
Species Id M060130
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
A Water Temperature: Between 21-27 degrees C
A Water Temperature: Specified in Comments
L Water Temperature: Between 21-27 degrees C
G Currents: specified in comments
G Turbidity: Clear water
E Water Temperature: Specified in Comments
G
G Substrate: Mud or silt
G Substrate: Specified in Comments
G Substrate: Sand
J Relation to Substrate: Attached - normally sessile
J Relation to Substrate: Specified in Comments
BA Water Temperature: Between 21-27 degrees C
BA Water Temperature: Specified in Comments
E
E
E
L
L
LIM
LIM
J
J
L Water Temperature: Greater than 27 degrees C
L Water Temperature: Between 21-27 degrees C
L Water Temperature: Between 15-21 degrees C
L Water Temperature: Specified in Comments
LIM Dissolved Oxygen: Low [less than 5 mg/l] oxygen concentrations
LIM Dissolved Oxygen: Specified in Comments
REFERENCES FOR ENVIRONMENTAL ASSOC_ - 57, 254 and 136
REFERENCES FOR LIMITING ENVIRONMENTAL ASSOC_ - 136
REFERENCES FOR FEEDING ADULT ENVIRONMENTAL ASSOC_ - 57 and 136
REFERENCES FOR RESTING ADULT ENVIRONMENTAL ASSOC_ - 57
REFERENCES FOR BREEDING ADULT ENVIRONMENTAL ASSOC_ - 57 and 136
Environment Associations - 1 (DRAFT) - Environment Associations
Species quahog, northern
Species Id M060130
Date 26 AUG 96
REFERENCES FOR JUVENILE ENVIRONMENTAL ASSOC_ - 136
REFERENCES FOR FEEDING JUVENILE ENVIRONMENTAL ASSOC_ - 57
REFERENCES FOR LARVAE ENVIRONMENTAL ASSOC_ - 136
REFERENCES FOR RESTING LARVAE ENVIRONMENTAL ASSOC_ - 57
REFERENCES FOR EGG ENVIRONMENTAL ASSOC_ - 57 and 136
COMMENTS ON ENVIRONMENTAL ASSOCIATIONS -
Temperature
Water temperature is the most important factor in growth and
reproduction. The harvest of the hard clam in Maine was highly correlated
(r = 0.80) to the August sea temperature 2 years previously (Sutcliff et
al. 1977). Dow (1977) recorded a highly significant correlation between
mean annual sea temperature and populations of adult hard clams.
Salinity
The salinities at which hard clams are found usually range from about 10
to 35 ppt, allowing for possible geographic differences. Belding (1931)
reported 23 to 32 ppt as the general range of tolerance. In Wellfleet
Harbor, Massachusetts, salinity in clam beds ranged from 20 to 34 ppt
(Curley et al 1972). The range of salinities in a New York clam habitat
was 15 to 35 ppt (MacKenzie 1979).*57*
Substrate
Numerous studies have shown that hard clams are more likely to live on a
sandy bottom than on a mud bottom (Allen 1954; Maurer and Watling 1973;
Mitchell 1974). Because water currents sort bottom substrates, there is a
high correlation between currents and bottom type; consequently, water
circulation may be the decisive element in the distribution of hard clams
(Greene et al. 1978).*57*
Currents
Water movement is important to all life stages of the hard clam.
Currents transport eggs and larvae and bring food to the adults. Hard
clams of Wickford Harbor, Rhode Island, live in current velocities less
than 0.5 m/sec (Landers 1953).*57*
Hard clams are euryhaline marine species sensitive to salinities below 12
ppt and thus are found only in the lower Bay from the mesohaline through the
polyhaline zone (12-32 ppt). Although found in a variety of substrates
including mud, hard clams prefer a firm bottom. They favor a mixture
containing sand or shell which provides points of attachment for juveniles
as well as protection from many predators *136*.
COMMENTS ON LIMITING ENVIRONMENTAL ASSOC_ -
Hard clams spawn when a critical temperature occurs. At salinities below
17.5 ppt, larvae fail to metamorphose and growth of juveniles ceases.
Optimal temperatures for larval growth range between 18 and 30 degrees C.
Growth ceases at oxygen concentrations below 2.4 mg/l *136*.
Environment Associations - 2 (DRAFT) - Environment Associations
Species quahog, northern
Species Id M060130
Date 26 AUG 96
COMMENTS ON RESTING ADULT ENVIRONMENTAL ASSOC_ -
Growth is reduced at water temperatures below 10 degrees C and growth stops
at 8 degrees C. Hard clams hibernate at temperatures below 6 degrees
C.*57*
COMMENTS ON FEEDING ADULT ENVIRONTAL ASSOC_ -
Pumping water, required for feeding, ceases below 6 degrees C and above 32
degrees C. The extension of the siphon also indicates pumping; the
temperature range for siphon extension is 1-34 degrees C.*57*
Food availability is a significant factor dictating their survival. Foods
of critical sizes are needed for the different life stages; with the cell
sizes generally ranging from 3-35 um *136*.
COMMENTS ON BREEDING ADULT ENVIRONMENTAL ASSOC_ -
Hard clams spawn at temperatures of 22 to 30 degrees C in Little Egg
Harbor, New Jersey (Carriker 1961) and from 21 to 25 degrees C in Barnegat
Bay, New Jersey (Kennish and Olsson 1975). They spawn in Delaware Bay at
25 to 27 degrees (Keck et al. 1975). Spawning is triggered by rising
temperatures.*57*
Hard clams spawn when a critical temperature occurs. Hard clams spawn at
temperatures of 22-24 degrees C *136*.
COMMENTS ON JUVENILE ENVIRONMENTAL ASSOC_ -
Hard clams favor a mixture containing sand or shell which provides points
of attachment for juveniles as well as protection from many predators. At
salinities below 17.5 ppt, larvae fail to metamorphose and growth of
juveniles ceases *136*.
COMMENTS ON FEEDING JUVENILE ENVIRONMENTAL ASSOC_ -
Because hard clams filter water to obtain food material, they also trap
other suspended material. Discharging this material reduces energy
available for growth (Pratt and Campbell 1956). Excess turbidity can clog
the filtering apparatus and cause death.*57*
COMMENTS ON LARVAE ENVIRONMENTAL ASSOC_ -
At salinities below 17.5 ppt, larvae fail to metamorphose and growth of
juveniles ceases. Optimal temperatures for larval growth range between 18
and 30 degrees C. Growth ceases at oxygen concentrations below 2.4 mg/l
*136*.
COMMENTS ON RESTING LARVAE ENVIRONMENTAL ASSOC_ -
Salinity is most critical during the egg and larval stages. The embyos in
Long Island Sound develop only in the range of 20 to 32 ppt; at 35 ppt only
10% develop (Davis 1958). Veliger survival is low during high rainfall
(Carriker 1961). Veliger growth is best at 20 to 27 ppt. Larvae
apparently require higher salinities than adults, and metamorphosis to seed
clams is rare below 18 ppt (Castagna and Chanley 1973).*57*
COMMENTS ON FEEDING LARVAE ENVIRONMENTAL ASSOC_ -
The optimum temperature range for larval growth is 22.5 to 25 degrees in
brackish water and 17.5 to 30 degrees C at a higher salinity (Davis and
Environment Associations - 3 (DRAFT) - Environment Associations
Species quahog, northern
Species Id M060130
Date 26 AUG 96
Calabrese 1964). According to Carriker (1961) larvae tolerate water
temperatures of 13 to 30 degrees C.*57*
The optimum salinity for larval survival is about 27 ppt (Davis and
Calabrese 1964). At about 22 ppt, the temperature tolerance was reduced.
Survival is highest between 21 and 29 ppt at 19 to 29.5 degrees C. The
larvae grew best between 22 and 30 ppt at 22 to 36 degrees C.*57*
Larvae prefer currents from 12 to 130 cm/sec (Carriker 1952). Densities
of larvae were low near the inlet of an estuary where tidal exchange was
greatest and currents fastest (Carriker 1961). The planktonic abundance
distribution of larvae is not affected by individual tidal stages, but
observations suggest that the abundance was highest 3 h after low tide
(Moulton and Coffin 1954).*57*
COMMENTS ON EGG ENVIRONMENTAL ASSOC_ -
Eggs require temperatures above 7.2 degrees C, but larval survival is
highest between 19 and 30 degrees C (Lough 1975). Growth is greatest from
22 to 26 degrees C. Embryos and veliger larvae develop abnormally and die
at 15 and 33 degrees C, but straight hinged larvae tolerate these
temperature extremes (Loosanoff et al. 1951). The minimum temperature for
growth when clams are fed naked dinoflagellates is 12.5 degrees C, but
higher temperatures are needed to digest algae (Davis andd Calabrese
1964).*57*
Embryos develop normally between 20 to 35 ppt; the optimum is about 28
ppt. The minimum salinity at which larvae survive was 15 ppt.*57*
Normal egg development occurs between 20-35 ppt salinity *136*.
Environment Associations - 4 (DRAFT) - Life History
Species quahog, northern
Species Id M060130
Date 26 AUG 96
LIFE HISTORY
Morphology/Identification aids
The hard clam has a thick shell, a violet interior border, and short
siphons (Verril 1873; Stanley 1970; Morris 1973). The mean length of the
thick solid shell is usually 60 to 70 mm, but sometimes reaches 120 to 130
mm. The ratios of length (L), height (H), and width (W) are: L/H = 1.25;
H/W = 1.52; L/W = 1.90. The thickness index (ratio of shell volume to
internal volume) is 0.60.
The external surface has numerous concentric lines that are conspicuous
and closely spaced near the outer margins, but more widely spaced around the
umbo, especially in younger shells. The center of each valve is smoother
than the distal portion. The umbo is far anterior and projects toward the
front of the shell. The shell is elliptical, somewhat pointed posteriorly,
and has a grayish-white exterior and a white interior with a dark violet
border near the margins. The colored part of the shell was fashioned into
wampum by the American Indians for use as money, hence the scientific name
(Morris 1973). The interior ventral margins are denticulate.
The internal anatomy also has distinctive characteristics (Verrill
1873). Short siphons are united from their bases to near the ends; the
incurrent siphon has a short fringe of tentacles. The siphon tubes are
yellowish or brownish orange toward the end, and may be streaked with dark
brown, black, or opaque white. The foot is large, muscular, and plow
shaped. The mantle lobes are separate along the front and ventral edges of
the shell and have thin edges folded into delicate frills, some of which are
elongated near the siphons. Foot and mantle edges are white.
The veliger larvae can be distinguished from other bivalves by the shape
of the shell and hinge structure (Loosanoff et al. 1966; Chanley and Andrews
1971; Lutz et al. 1982). The margin of the shell is circular, tapering
toward the hinge; the hinge is short and narrow.*57*
Spawning
The spawning season extends from March through November, depending on
latitude and temperature. In temperate climates, spawning is heaviest in
July. The peak is in May in the York River, Virginia, and is progressively
later in Raritan Bay, New Jersey, and Narragansett Bay, Rhode Island.
Individual female hard clams require 2.0 to 2.5 months to complete spawning,
but the release of eggs is greatest during the initial spawning of the
season. Spawning is more intense during neap than during spring tides,
presumably because water temperatures are higher during neap tides. Water
temperature is the decisive factor governing final gamete maturation. In a
2-year study in Lower Little Egg Harbor, New Jersey, the median daily
spawning temperature was 25.7 degrees C. and the range was 22-30 degrees
C.*57*
Fecundity and Eggs
The average number of eggs released by a 60 mm female in nature is about 2
million. About 2,000 spermatozoa are shed for each ovum. The spherical
eggs are 78 micrometers in diameter and yolk granules are closely packed. A
large gelatinous capsule distinguishes the hard clam egg from the eggs of
other mollusks. Eggs are released through the excurrent siphon, and the
capsule swells after contact with seawater until it is 3.2 times the
Life History - 1 (DRAFT) - Life History
Species quahog, northern
Species Id M060130
Date 26 AUG 96
diameter of the egg. Because the gelatinous capsule imparts buoyancy, the
eggs are pelagic and carried by tidal and coastal currents. Spermatozoa
swimming in water come into contact with and penetrate the capsule,
fertilizing the egg. After 10 hours the embryo developing within the
capsule becomes covered with cilia. The lashing of the cilia tears the
membrane and gelatinous capsule and the ciliated gastrula escapes into the
water. Eggs may be carried as far as 25 km from the spawning site.*57*
Larvae
Trochophore larvae are formed about 12 to 14 hours after hatching. The
shape resembles a child's top, and the cilia on the blunt anterior end cause
spiral swimming and rotation around the long axis in either direction. A
functional mouth develops and the larva begins feeding on suspended
particulates, especially dinoflagellates. The larvae concentrate about 1 m
below the surface during daylight but at night are more evenly mixed in the
water column. About 24 h after hatching, a shell gland forms opposite the
mouth, a thin transparent shell is secreted, and the larvae becomes a
veliger. The veliger drifts in ocean and estuarine currents, but it is able
to move 7 to 8 cm/min vertically by extending the ciliated velum. Vertical
migration is stimulated by turbulance, which carries veligers into
horizontal water currents for transport. The number of veligers is greatest
in the water column 3 h after low tide. By drifting with the incoming tide,
the veligers are transported into the estuary and to sea. Veligers of hard
clams are abundant in the zooplankton in estuaries during the summer, where
densities may exceed 500/l. The veliger stage lasts 7 to 30 days, depending
on temperature. Metamorphosis of the veliger of the hard clam is a gradual
process that takes place 16 to 30 days after hatching at 18 degrees C., 11
to 22 days at 24 degrees C. and 7 to 16 days at 30 degrees C.*57*
Juvenile Seed Clam
When the veliger becomes 0.2 to 0.3 mm long, the shell thickens, a foot
replaces the velum, and a byssal gland develops, indicating metamorphosis to
the seed clam. Metamorphosis is inhibited at salinities below 17.5 to 20
parts per thousand (ppt), ensuring that seed clams avoid setting in an
environment with salinities unsuitable for adults. The byssal gland of the
seed clam secretes a tough thread, the byssus, which anchors the clam to the
substrate. Seed clams are set more densely in sand than mud; bits of shell
or detritus may also serve as anchors. In Little Egg Harbor, New Jersey,
the seed clams prefer to set on a firm surface with a thin layer of detritus
or on shells coated with mud. To move, the clam byssus is cast off and the
foot is used for locomotion. When the young clam reaches a desirable
habitat, it spins a new byssus and reattaches to a small object. Seed clams
set without cover are subject to heavy predation. Normally they do not live
in areas exposed to wave action or strong currents, but in the absence of
predators.
Adults
The adult hard clam lives in the substrate and burrows with a muscular foot.
In the first 38 days after first burrowing, adults moved laterally an
average of only 5 cm and a maximum of 15 cm from the point of origin. Hard
clams are most abundant in the lower estuary and are seldom found in the
upper estuary where salinities are lower. The are absent in places with
salinity less than 15 ppt in upper Delaware Bay and in upper Chesapeake Bay.
Life History - 2 (DRAFT) - Life History
Species quahog, northern
Species Id M060130
Date 26 AUG 96
Some populations are oceanic, e.g. those in the shoals of Nantucket Sound.
An offshore population is located between Cape Lookout and Beaufort Inlet,
North Carolina.*57*
Hard clams are euryhaline marine species sensitive to salinities below 12
ppt and thus are found only in the lower Bay from the mesohaline through the
polyhaline zone (12-32 ppt). Although found in a variety of substrates
including mud, hard clams prefer a firm bottom. They favor a mixture
containing sand or shell which provides points of attachment for juveniles
as well as protection from many predators. Hard clams spawn when a critical
temperature occurs. Hard clams spawn at temperatures of 22-24 degrees C.
Normal egg development occurs between 20-35 ppt salinity. At salinities
below 17.5 ppt, larvae fail to metamorphose and growth of juveniles ceases.
Optimal temperatures for larval growth range between 18 and 30 degrees C.
Growth ceases at oxygen concentrations below 2.4 mg/l *136*.
LIFE HISTORY CODES -
Native
REFERENCES FOR LIFE HISTORY- 57
Life History - 3 (DRAFT) - Management Practices
Species quahog, northern
Species Id M060130
Date 26 AUG 96
MANAGEMENT PRACTICES
RESULT MANAGEMENT PRACTICE
Beneficial Maintaining undisturbed/undeveloped areas
Beneficial Mariculture activities
Beneficial Controlling pollution [thermal, chemical, physical]
Beneficial Controlling sedimentation
Adverse Dredging
REFERENCES FOR BENEFICIAL MANAGEMENT PRACTICES - 57
COMMENTS ON MANAGEMENT PRACTICES -
The hard clams' habitat is vulnerable to coastal construction projects and
pollution from urban and industrial development. Because adults do not
migrate, repopulation of over-fished hard clam beds depends on the transport
of larvae from other areas and several years for growth, maturation, and
reproduction. Any disturbance, however temporary, may cause a long-term
impact.*57*
Dredging of coastal waters reduces the abundance of hard clams in the area
of impact. For example, hard clams in the path of a dredged channel through
a lagoon on Long Island, New York, were destroyed, and those on either side
of the path were adversely affected by sedimentation (Kaplan et al. 1974).
Hard clams further than 400 m from the dredge site were unaffected.
Commercial clammers in this area reported no noticable reduction in harvest
the following year, whereas scientists found a significant reduction in
standing crop. In Boca Ciega, Florida, the hard clam population failed to
return to its previous abundance 13 years after dredging (Taylor and Saloman
1968).*57*
Hard clams are taken commercially with hoes, bullrakes, hand tongs, and
power dredges (Engle 1970). Of the commercial landings from Narragansett
Bay, 90% are taken by handraking (Holmsen 1966), whereas in Chesapeake Bay,
95% of hard clams are taken with patent tongs (Haven and Loesch 1973).
Although a power dredge is effective, it is not permitted in many areas,
even though it disturbs the substrate no more than bullraking, and all
evidence of harvesting disappears within 500 days (Glude and Landers 1953).
A power dredge with escalator increases the catch of the more valuable small
clams, but causes disturbance of the substrate (Godcharles 1971). Because
dredging destroys seagrasses and benthic algae and recolonization is slow,
dredging has a relatively long-term environmental impact.*39*
Pollution in Narragansett Bay affects the quahog industry because the
quahog's filter-feeding process concentrates not only food particles but
also many pollutants-including disease-causing bacteria and viruses, and
toxic compounds. Thus, even pollutants that are present only in low levels
in the water can accumulate to dangerous levels in filter feeders.
About 1/4 of Narragansett Bay's total area, including the Providence River
and Mount Hope Bay, is permanently closed to shellfishing because of the
danger of sewage contamination. In addition, a portion of the upper bay is
closed after rainfalls because antiquated "combined sewage" systems in
Providence and other towns allow inadequately treated sewage to enter the
Management Practices - 1 (DRAFT) - Management Practices
Species quahog, northern
Species Id M060130
Date 26 AUG 96
bay during rainstorms.*279*
In some parts of New England, it is also important to watch for shellfishing
closures due to red tides. Shellfish taken from a red tide area can contain
a toxin that causes paralytic shellfish poisoning. However, no occurrences
of toxic red tide have been recorded in Narragansett Bay.*279*
Management Practices - 2 (DRAFT) - References
Species quahog, northern
Species Id M060130
Date 26 AUG 96
References
39* Stanley, J., R. DeWitt. 1983. Species Profiles: Life Histories
and Environmental Requirements of Coastal Fishes and
Invertebrates (North Atlantic)--Hard Clam. U.S. Fish and
Wildlife Service Biol. Rep. 82(11.18) pp 19.
57* Stanley, J. 1985. Species Profiles: Life Histories and
Environmental Requirements of Coastal Fishes and Invertebrates
(Mid-Atlantic) -- Hard Clam. U.S. Fish and Wildlife Service
Biol. Rep. 82(11.41) pp 24.
136 * Chesapeake Bay Program. 1988. Habitat Requirements for
Chesapeake Bay Living Resources. Chesapeake Executive
Council pp 86.
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