(DRAFT) - Taxonomy
Species clam, common littleneck
Species Id M060002
Date 26 AUG 96
TAXONOMY
NAME - clam, common littleneck
OTHER COMMON NAMES - Pacific littleneck
ELEMENT CODE -
CATEGORY - Aquatic Molluscs
PHYLUM AND SUBPHYLUM - Mollusca,
CLASS AND SUBCLASS - Bivalvia,
ORDER AND SUBORDER - Veneroida,
FAMILY AND SUBFAMILY - Veneridae,
GENUS AND SUBGENUS - Prothaca,
SPECIES AND SSP - staminea,
SCIENTIFIC NAME - Prothaca staminea
AUTHORITY - Conrad, 1837
TAXONOMY REFERENCES - 186
COMMENTS ON TAXONOMY -
This species is also known as native littleneck clam, rock cockle, bay
cockle, hardshell clam, Tomales Bay cockle, rock clam, ribbed carpet shell,
steamer clam and Pacific littleneck *13*.
Taxonomy - 1 (DRAFT) - Status
Species clam, common littleneck
Species Id M060002
Date 26 AUG 96
STATUS
Coded Status
Sport Fish
Commercial/consumption
Commercial
REFERENCES FOR STATUS - 3
COMMENTS ON STATUS -
This species is taken in both intertidal and subtidal harvests. It is one of
the most highly distributed hardshell clams along the entire coast of the
northwest region. It is one of the most popular species harvested
intertidally for recreation purposes in the Puget Sound and along the
Washington coast. An estimated 2.3 million pounds were harvested from public
beaches during 774,000 user trips. This species is also farmed in central
Puget Sound *3*.
Status - 1 (DRAFT) - Distribution
Species clam, common littleneck
Species Id M060002
Date 26 AUG 96
DISTRIBUTION
Distribution - 1 HABITAT ASSOCIATIONS
HABITAT - MARINE
REFERENCES FOR HABITAT - 67
LAND USE -
Bays and Estuaries
REFERENCES FOR LAND USE - 67
NATIONAL WETLAND INVENTORY CODES
NWI NWICLS NWIMOD NWISPEC
Estuarine FL1 L 3
Estuarine FL2 L 3
Estuarine, subtidal FL3 L 3
REFERENCES FOR NWI - 67
COMMENTS ON HABITAT ASSOCIATIONS -
Littleneck clams live in the coarse, sand to mud sediments of bays, sloughs
and estuaries in California. On the open coast, they live in nearly any
area where there are rocky points or reefs made up of small cobbles over
coarse sand. In southeastern and south-central Alaska, littleneck clams
are common on sandy gravel beaches. In some coastal waters of California,
there are wide fluctuations in clam abundance because heavy runoff from
creeks causes extensive sanding-in of cobble beaches which decimates clam
habitat. Littleneck clam populations in those areas that have undergone
sanding-in may require as many as 5 years to recover.
Littleneck clams live often on small beaches that exist in pockets on
rocky shorelines, or in small patches of larger beaches. The best beaches
for littleneck clams are those with coarse sand or fine gravel mixed with
mud, stones, or shells. Apparently littleneck clams do poorly in fine
sand.*67*
Depth:
Littleneck clams are most abundant in the lower part of the intertidal
zone and subtidally to a depth of 3 m. Maximum burrowing depth is about 15
cm. In Alaska, clams live in the 1.5 to 1.0 m tidal range.*67*
ANIMAL/PLANT SPECIES ASSOCIATIONS -
The littleneck clam has many predators. In Mugu Lagoon, California, it was
observed that the snail Polinices reclusianus and the crab, Cancer anthonyi,
caused fatalities. Littleneck clams make up 16% of the diet of the octopus
Octopus dofleini. The clams eaten were 15 to 70 mm long, but most were 40
to 50 mm long. The intensity of predation was related to distance between
the den of the octopus and the gravel beaches where the clams lived.
Two carnivorous gastropods, Forreria belcheri and Shaskyus festivus, prey
on littleneck clams. Sea stars (Pycnopodia helianthoides) prey on
littleneck clams in Prince William Sound, Alaska. The sea otter (Enhydra
lutris) also is a major predator of clams. Other predators are polychaetes,
fishes and ducks. Small fishes have been found to nip on the siphons of
littleneck clams, reducing clam growth.
In transplant experiments in Mugu Lagoon, California, the deep dwelling
bivalve Sanguinolaria nuttallii has no discernable influence on the
shallow-dwelling littleneck clam.*67*
REFERENCES FOR SPECIES ASSOCIATIONS - 67
Habitat Associations - 1 (DRAFT) - Food Habits
Species clam, common littleneck
Species Id M060002
Date 26 AUG 96
FOOD HABITS
TROPHIC LEVEL -
FILTERER
REFERENCES FOR TROPHIC LEVEL - 67
LIFESTAGE FOOD FOOD PART
Adult Plankton Not Specified
General Plankton Not Specified
REFERENCES FOR GENERAL FOOD - 67
REFERENCES FOR ADULT FOOD - 67
COMMENTS ON FOOD -
The littleneck clam is a suspension feeder, collecting everything in the
plankton small enough to be ingested. The size of particle ingested is
controlled by the size of the mouth or opening or the life stage. Clam
postlarvae can feed only on particles under 10 micrometers in diameter,
primarily benthic diatoms and perhaps sediment bacteria. Because most
littleneck clams live in the intertidal zone, most feeding is at high tide.
Unlike many species of clams, littlenecks can move by using their foot and
reburrow. Clams in heavily populated areas may move to less densely
populated areas, and clams exposed by dredging can reburrow after dredging
is completed.*67*
COMMENTS ON LARVAE FOOD -
The littleneck clam is a suspension feeder, collecting everything in the
plankton small enough to be ingested. The size of particle ingested is
controlled by the size of the mouth or opening or the life stage. Clam
postlarvae can feed only on particles under 10 micrometers in diameter,
primarily benthic diatoms and perhaps sediment bacteria. Because most
littleneck clams live in the intertidal zone, most feeding is at high tide.
Food Habits - 1 (DRAFT) - Environment Associations
Species clam, common littleneck
Species Id M060002
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: Below 15 degrees C
L Water Temperature: Specified in Comments
L
A
G Estuarine habitat zone: bay
G Substrate: Sand
G Substrate: Mud or silt
G Relation to Substrate: Occurs in substrate [penetrating]
LIM Stability of Bottom: Stable
LIM Biodegradable Organics: Clean waters that have not been exposed to pollutio
REFERENCES FOR ENVIRONMENTAL ASSOC_ - 67
REFERENCES FOR LIMITING ENVIRONMENTAL ASSOC_ - 67
REFERENCES FOR ADULT ENVIRONMENTAL ASSOC_ - 67
REFERENCES FOR LARVAE ENVIRONMENTAL ASSOC_ - 67
COMMENTS ON ENVIRONMENTAL ASSOCIATIONS -
Littleneck clams live in the coarse, sand to mud sediments of bays, sloughs
and estuaries in California. On the open coast, they live in nearly any
area where there are rocky points or reefs made up of small cobbles over
coarse sand. In southeastern and south-central Alaska, littleneck clams
are common on sandy gravel beaches. In some coastal waters of California,
there are wide fluctuations in clam abundance because heavy runoff from
creeks causes extensive sanding-in of cobble beaches which decimates clam
habitat. Littleneck clam populations in those areas that have undergone
sanding-in may require as many as 5 years to recover.
Littleneck clams live often on small beaches that exist in pockets on
rocky shorelines, or in small patches of larger beaches. The best beaches
for littleneck clams are those with coarse sand or fine gravel mixed with
mud, stones, or shells. Apparently littleneck clams do poorly in fine
sand.*67*
Depth:
Littleneck clams are most abundant in the lower part of the intertidal
zone and subtidally to a depth of 3 m. Maximum burrowing depth is about 15
cm. In Alaska, clams live in the 1.5 to 1.0 m tidal range.*67*
Environment Associations - 1 (DRAFT) - Environment Associations
Species clam, common littleneck
Species Id M060002
Date 26 AUG 96
COMMENTS ON LIMITING ENVIRONMENTAL ASSOC_ -
Heavy metals have been concentrated in littleneck clams because long-lived
sedentary animals commonly concentrate such contaminanats. Littleneck
clams are highly sensitive to copper whcih is used in antifouling boat
paints. A 15% mortality of clams was reported at copper concentrations of
7 and 18 micrograms per liter after 30 days of exposure. At 39 and 82
micrograms per liter, mortality was 86% and 97%, respectively, after 30
days of exposure. Copper concentrates in the gills and disrupts regulation
of cellular sodium and potassium.
The uptake of heavy metals in littleneck clams has been monitored in
Elkhorn Slough, California. Shell concentrations (ppm dry weight) were as
follows; Ag, 5.8; Cd, 2.9; Cr, <5.7; Cu, 11.5; Mn, 16.8; Pb, <9.0; and Zn,
9.2. The quantities of heavy metals in the littleneck clam generally were
lower than those in other shellfish in California. Crabs consumed more
clams from oiled than from unoiled sand because clams do not burrow as deep
in oiled sand. Slow burrowing in oiled snad also led to increased
predation. Small clams are far more vulnerable to crab predation than
large ones.*67*
COMMENTS ON ADULT ENVIRONMENTAL ASSOC_ -
Adult littleneck clams can withstand water temperatures from near freezing
to 25 degrees C, and the salinity tolerance for adults ranges from about 20
ppt or less, to 30 ppt in Prince William Sound, Alaska.*67*
COMMENTS ON LARVAE ENVIRONMENTAL ASSOC_ -
Larval littleneck clams normally live in a relatively narrow range of
temperature and salinity. Near Newport, Oregon, the optimum water
temperature range is 10 to 15 degrees C and the optimum salinity range is
27 to 32 ppt.*67*
Environment Associations - 2 (DRAFT) - Life History
Species clam, common littleneck
Species Id M060002
Date 26 AUG 96
LIFE HISTORY
Spawning: The sexes of the common littleneck clam are separate. The time of
spawning varies throughout its range, depending largely on water
temperature. Early studies in British Columbia report spawning in January
and in February and March. The growth of gametes reaches a peak in March
and spawning begins in April. Few spawn later than September. The male
spawning cycle parallels that of the female, but for unknown reasons lags
behind that of the female by about 1 month. In British Columbia, most clams
spawn in late spring but some may spwn off and on throughout the summer.
In Alaska, spawning starts in mid-July when the water temperature is about
8 degrees C. In Prince William Sound, Alaska, spawning begins in late May
to mid-June and continues into September. In summer, water temperature
fluctuations are unusually strong, so there may be two periods of high
temperature and two corresponding spawning peaks. In a warmer than normal
year, only one temperature and spawning peak may be expected.
In Mugu Lagoon, California, it was reported that June marks the beginning
of the season of gamete release. It was also observed that gonad weight
declined sharply between June and December, indicating spawning between June
and December.
During spawning, the eggs and sperm are discharged through the siphon and
mass fertilization takes place in the open water.
Eggs and Larval Stages:
The embryos develop into a trocophore larval stage (60-80 micrometers)
about 12 hours after fertilization. The veliger (straight-hinge stage)
develops in the next 24 h. A ciliated velum develops and helps the larva
swim and maintain itself in the upper part of the water column. Larvae feed
on phytoplankton and are about 0.15 mm long after 1 week. The veligers
develop an umbo (prodissoconch) and may reach a length of 0.26 to 0.28 mm in
2 weeks. Larvae up to 0.5 mm long were found in British Columbia. Prior to
metamorphosis, the veligers develop a foot and an eye spot, move to the
bottom, and search for a suitable surface on which to settle. Once a
suitable surface is found, the larvae undergo metamorphosis and attach to
the surface by secreting byssal threads. Depending on food supply and
temperature, the planktonic larval stage generally lasts about 3 weeks.
The larval stage is a critical one and breeding success or failure is
frequently determined at this time. Larvae are at the mercy of currents and
may be carried away from settling areas and perish.
Postlarvae and Recruitment:
Postlarvae are epifaunal and mortality may be high. After settlement,
mortality is highest during or at the end of the first year. Highest
mortality is in the winter.
In Mugu Lagoon, California, clams that had set in mid-April in sand were
7.6 mm long by mid-June whereas those in mud were 8.3 mm long by mid-June.
Unlike the Washington clams, Saxidomus, which remain permantly at site of
settlement, young littleneck clams can crawl, using their foot, to other
areas.*67*
The extent of annual recruitment of littleneck clams varies greatly
between areas. It was found that Protothaca had the highest variance in
numbers of all species collected in 10 sampling periods over a 3-year
period, suggesting a high variability in recruitment. In sand,
Life History - 1 (DRAFT) - Life History
Species clam, common littleneck
Species Id M060002
Date 26 AUG 96
experimentally increased adult densities had no significant effect on
recruitment, whereas in mud, high adult densities reduced recruitment up to
60%. In Prince William Sound, Alaska, the clam's northern limit,
recruitment was erratic and there was little recruitment from 1967 to 1971,
probably due to poor spawning.
Maturity and Life-Span:
The only data on maturity are from north Pacific populations. At Woods
Island, Ladysmith Harbor, British Columbia, sexual differentiation was
apparent when clams were 15 to 35 mm long or during their second or third
year of life. Mature clams were usually 22 to 35 mm long. At Prince
William Sound, Alaska, the youngest sexual mature clams was 3 years old and
13 mm long. In British Columbia, mature 2 year old clams were found; about
one-half of the clams spawned for the first time at the end of the second
year of life.
Growth Characteristics:
Some scientists believe that littleneck clams can be accurately aged by
counting the rings on the shell. The rings are much closer together when
growth slows in the winter because of low metabolism. However, excessive
variation in ring patterns were found in the same population from Newport
Bay, Oregon. Also disturbances can interrupt growth of rings. Rings can be
evaluated as an aging tool by marking the shell and then recovering the
clams for examination at a later date.
The growth of littleneck clams varies throughout its range. Growth curves
are available for clam populations from Alaska, British Columbia, and
California and for an experimental plot in Oregon. In Prince William Sound,
Alaska, clams reach the marketable length of 30 mm in 8 years, but at
Porpoise Island, southeast Alaska, clams reach this length in 4 to 5 years.
In waters near Sidney, British Columbia, the range of length of the clams
for each year of life was as follows: 1st year, 11-17 mm; 2nd year, 22-33
mm; 3rd year, 36-51 mm; 4th year, 37-51 mm; 5th year, 43-55 mm; 6th year,
44-57 mm; 7th year, 47-60 mm; 8th year 49-61 mm; 9th year, 51-62 mm; and 10
year, 54-63 mm. The authors noted wide differences in growth rates among
the years.
In Mugu Lagoon, California, the growth rate of littleneck clams was
consistently depressed at experimentally induced high intraspecific
densities. In mud the clams linear growth declined more than in sand as
intraspecific density increased. In Alaska, clams at the higher tide levels
has the best growth. At Kiket Island, Washington, however, the best growth
was near mean lower low water and less rapid at higher and lower tide
levels. Growth was better on the north side of the island because of more
stable water temperatures and salinities.
In British Columbia, littleneck clams are 37 mm long in 3.5 to 4 years and
63 mm long in 10 years. In the State of Washington, it takes 4 to 6 years
for clams to reach commercial length (1.5 inches). In Oregon, clams planted
on artificial substrate were 37 mm long in 42 months. In California, clams
reach legal size (1.5 inches) in 2 years, although in Mugu Lagoon it appears
to take up to 7 years to reach legal size.*67*
LIFE HISTORY CODES -
Spawning Site: Standing Water
Spawning Site: Sand
Life History - 2 (DRAFT) - Life History
Species clam, common littleneck
Species Id M060002
Date 26 AUG 96
LIFE HISTORY CODES -
Spawning Site: Gravel
Gestation/Incubation Period (insemination to parturati
Parental Care of Young: No care given young
REFERENCES FOR LIFE HISTORY- 67
Life History - 3 (DRAFT) - Management Practices
Species clam, common littleneck
Species Id M060002
Date 26 AUG 96
MANAGEMENT PRACTICES
RESULT MANAGEMENT PRACTICE
Beneficial Controlling pollution [thermal, chemical, physical]
REFERENCES FOR BENEFICIAL MANAGEMENT PRACTICES - 67
COMMENTS ON MANAGEMENT PRACTICES -
In California, there was commercial digging prior to World War II, but now
most of the beds have been overexploited and only sport clamming is
permitted. San Francisco Bay is the only large area in California with
sufficient clam abundance to support a commercial fishery, but because of
pollution, all clams from San Francisco Bay would have to be depurated
before sale. Because of daily catch limit of 50 clams, a commercial fishery
is unlikely to develop. Littleneck clams are not harvested in Prince William
Sound or elsewhere in Alaska as a consequence of paralytic shellfish poison
or PSP. Eating shellfish that have consumed large amounts of the
poison-producing microscopic dinoflagellate Gonyaulax catenella can cause
serious illness. The major problem of the sport clam fishery in California
is the discharge of sewage and animal wastes into estuaries and nearshore
marine waters. Although there is a coastwide warning of the dangers of
paralytic shellfish poison from May 1 to October 31, the poison is not a
problem.*67*
Management Practices - 1 (DRAFT) - References
Species clam, common littleneck
Species Id M060002
Date 26 AUG 96
References
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.
American Fisheries Society Special Publication 16. (ed.):277.
67* Shaw, W. N. 1986. Species Profiles: Life Histories and
Environmental Requirements of Coastal Fishes and Invertebrates
(Pacific Southwest) -- Common Littleneck Clam. U.S. Fish and
Wildlife Service Biol. Rep. 82(11.46) pp 11.
References - 1