(DRAFT) - Taxonomy
Species Pacific gaper
Species Id M060014
Date 26 AUG 96
TAXONOMY
NAME - Pacific gaper
OTHER COMMON NAMES - Washington clam, big-neck clam, blue clam, empire clam, gaper clam, great horseneck clam, otter-shell clam, rubberneck clam and summer clam
ELEMENT CODE -
CATEGORY - Aquatic Molluscs
PHYLUM AND SUBPHYLUM - Mollusca,
CLASS AND SUBCLASS - Bivalvia,
ORDER AND SUBORDER - Veneroida,
FAMILY AND SUBFAMILY - Mactridae,
GENUS AND SUBGENUS - Tresus,
SPECIES AND SSP - nuttallii,
SCIENTIFIC NAME - Tresus nuttallii
AUTHORITY -
TAXONOMY REFERENCES - 01
Taxonomy - 1 (DRAFT) - Status
Species Pacific gaper
Species Id M060014
Date 26 AUG 96
STATUS
Coded Status
Commercial
Commercial/consumption
REFERENCES FOR STATUS - 01
Status - 1 (DRAFT) - Distribution
Species Pacific gaper
Species Id M060014
Date 26 AUG 96
DISTRIBUTION
Distribution - 1 HABITAT ASSOCIATIONS
LAND USE -
Bays and Estuaries
REFERENCES FOR LAND USE - 01
NATIONAL WETLAND INVENTORY CODES
NWI NWICLS NWIMOD NWISPEC
Marine, intertidal N 2
Estuarine, subtidal L 2
Estuarine, intertidal N 2
Marine, subtidal L 2
REFERENCES FOR NWI - 01
COMMENTS ON HABITAT ASSOCIATIONS -
This species is a subtidal and lower intertidal suspension/filter feeding
bivalve.*01*
Clam beds are sometimes closed to harvest because of paralytic shellfish
poisoning. Other beds are permanently closed to harvesting because of
contamination by coliform bacteria. As a result of pollution in Washington
waters, over 25% of the potential areas for subtidal clam harvesting are
closed. In California, clams in estuaries such as San Francisco Bay are not
commonly harvested because of pollution.*01*
ANIMAL/PLANT SPECIES ASSOCIATIONS -
Pea crabs (Pinnixa faba and occasionally P. littoralis) can be found in the
Pacific gaper's mantle cavity. The hard, leathery tips are often covered
with many different species of plants and animals. The Pacific gaper appears
to harbor pea crabs only in the southern part of its range. This species is
an intermediate host for the tapeworm, Echeneibothrium sp., whose definitive
host is the bat ray ( Myliobatis californica).*01*
REFERENCES FOR SPECIES ASSOCIATIONS - 01
COMMENTS ON SPECIES ASSOCIATIONS -
Predators include those that prey on T. capax, especially worms, snails,
crustaceans, fish, and mammals. Common predators include moon snails
(Polinices spp.), Dungeness crab (Cancer magister), bat ray (Myliobatus
californica), leopard shark (Triakis semifasciata), starry flounder
(Platichthys stellatus), sea stars (Piaster spp.), and sea otters (Enhydra
lutris). Many planktivorous organisms prey on Pacific gaper eggs and
larvae.*01*
Factors Influencing Populations: Sea otters prefer to feed in areas where
Pacific gaper densities are high and composed of small individuals unable to
burrow deeply because of sediment charactersistics; large Pacific gapers in
soft sediments are resistant to sea otter predation. The Pacific gaper may
compete with T. capax, however T. capax is more common in gravel-shell soils
whereas T. nuttallii is more common in pure sand substrates. The Pacific
gaper also burrows deeper than T. capax and thus avoids temporary freezing
conditions. No information is available concerning mortality rates, but very
high mortality rates probably occur during larval and early juvenile stages,
becoming lower as clams mature. Annual juvenile recruitment varies widely
and probably has a major effect on the population structure.*01*
Habitat Associations - 1 (DRAFT) - Food Habits
Species Pacific gaper
Species Id M060014
Date 26 AUG 96
FOOD HABITS
TROPHIC LEVEL -
FILTERER
REFERENCES FOR TROPHIC LEVEL - 01
LIFESTAGE FOOD FOOD PART
General Phytoplankton Not Specified
General Zosteraceae Not Specified
General Detritus Not Specified
REFERENCES FOR GENERAL FOOD - 01
COMMENTS ON FOOD -
Food items include suspended diatoms, flagellates, dinoflagellates, and
detritus. Detritus may include particles of eelgrass (Zostera marina).
This species is a suspension/filter feeder. Food particles are transported
via the inhalant siphon and are filtered from the water by the gills, sorted
by the palps, and passed to the mouth.*01*
Food Habits - 1 (DRAFT) - Environment Associations
Species Pacific gaper
Species Id M060014
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
G Water Temperature: Between 15-21 degrees C
G Water Temperature: Specified in Comments
G Water Temperature: Below 15 degrees C
G
G Dissolved Oxygen: Unknown
G Total Dissolved Solids: Unknown
G Nutrient [Phosphorus and Nitrogen]: Unknown
G Substrate: Mud or silt
G Substrate: Sand
G Substrate: Specified in Comments
G Relation to Substrate: Occurs in substrate [penetrating]
G Bottom Type [Aquatic]: Mud or silt
G Bottom Type [Aquatic]: Sand
G Bottom Type [Aquatic]: Gravel
G Bottom Type [Aquatic]: Specified in Comments
G Specific Conductances [uMhos]: Unknown
G Water Depth Preference: 1-5 ft.
G Water Depth Preference: 5-10 ft.
G Water Depth Preference: 10-25 ft.
G Water Depth Preference: 25-50 ft.
G Water Depth Preference: 50-100 ft.
G Water Depth Preference: Specified in Comments
G Estuarine habitat zone: bay
G Estuarine habitat zone: sound
G Estuarine habitat zone: specified in comments
G Currents: tidal
REFERENCES FOR ENVIRONMENTAL ASSOC_ - 01
COMMENTS ON ENVIRONMENTAL ASSOCIATIONS -
The species occurs in polyhaline-euhaline waters and temperatures of 1-21
degrees C. Freezing temperatures on mud flats may limit this species'
northern distribution. *01*
The Pacific gaper is most abundant in sediments consisting of fine sand or
firm sandy mud. But it is also found in relatively firm sediments
Environment Associations - 1 (DRAFT) - Environment Associations
Species Pacific gaper
Species Id M060014
Date 26 AUG 96
consisting of sand, silty-sand, sandy-clay,and gravel. Sediment structure
affects burrowing depth; clams burrow deeper in mud and sand substrates
than clay substrates.*01*
Eggs and larvae are pelagic. Juveniles and adults are benthic infauna;
adults may burrow to depths of 1 m.*01*
Eggs and larvae are neritic. Juveniles and adults are found primarily in
bays and estuaries, but may also occur in protected coastal waters.
Juveniles and adults occur from the lower intertidal zone to 30 m below mean
lower low water (MLLW). In Puget Sound, they are most abundant from 1-5 m
below MLLW.
Environment Associations - 2 (DRAFT) - Life History
Species Pacific gaper
Species Id M060014
Date 26 AUG 96
LIFE HISTORY
This species is a large, subtidal and lower intertidal suspension/filter
feeding bivalve. Eggs and larvae are pelagic. Juveniles and adults are
benthic infauna; adults may burrow to depths of 1 m (usually found 25-50 cm
deep).*01*
Eggs and larvae are dispersed by currents. Juveniles and adults do not move
laterally once they become established. Small Pacific gapers have the
ability to reburrow after being disturbed, but like T. capex, older, larger
clams (>60 mm shell length) lose the ability to reburrow. However, since the
most larger clams live deep within the sediment (up to 1 m) they are
protected from most natural disturbances. Peak settlement for spat occurs in
May in Central California and probably July in Puget Sound.*01*
Reproduction: The Pacific gaper is gonochoristic, oviparous, and
iteroparous. It is a broadcast spawner; eggs are fertilized externally.
Mating/Spawning: Spawning occurs year-round, depending on geographical
location. Spawning occurs during summer in northern regions such as British
Columbia and Puget Sound. Spawning occurs from spring to fall for much of
California, and year-round in Central California, with a peak from February
to April when temperatures are lowest. The wide daily water temperature
fluctuations in Central California may explain the occurrence of year-round
spawning.*01*
Fecundity: unknown
Egg Size and Embryonic Development: Egg size is unknown, however embryonic
development is indirect and external.*01*
Age and Size of Larvae: Larvae are probably 0.06-0.28 mm in diameter. In
Elkhorn Slough, Calif., the duration of the larval stage is estimated to be
21-30 days. Spat require 10 days to grow to 2 mm and 25 days to grow to 5
mm.*01*
Juvenile Size range: Juveniles are 0.26 mm to 51.0-71.0 mm in diameter;
small clams (4 mm) grow 0.25 mm/day. One year old clams average 50 mm in
shell length.*01*
Age and Size of Adults: This species matures in about 2 years and between
51.0-70.0mm shell length. The Pacific gaper may live to 17 years, with a
shell length as great as 200 mm.*01*
LIFE HISTORY CODES -
Foraging Strategy: Filtering
Breeding/Spawning Season: January
Breeding/Spawning Season: February
Breeding/Spawning Season: March
Breeding Spawning Season: April
Breeding/Spawning Season: May
Life History - 1 (DRAFT) - Life History
Species Pacific gaper
Species Id M060014
Date 26 AUG 96
LIFE HISTORY CODES -
Breeding/Spawning Season: June
Breeding/Spawning Season: July
Breeding/Spawning Season: August
Breeding/Spawning Season: September
Breeding/Spawning Season: October
Breeding/Spawning Season: November
Breeding/Spawning Season: December
Parental Care of Young: No care given young
Dispersion: Random
REFERENCES FOR LIFE HISTORY- 01
Life History - 2 (DRAFT) - Management Practices
Species Pacific gaper
Species Id M060014
Date 26 AUG 96
MANAGEMENT PRACTICES
RESULT MANAGEMENT PRACTICE
Beneficial Regulating harvest of species being described
Beneficial Predator control
Beneficial Public education - publicity
Beneficial Maintaining undisturbed/undeveloped areas
Beneficial Controlling pollution [thermal, chemical, physical]
Adverse Dredging
Adverse Underwater explosions
Adverse Changing tidal cycle/ current patterns
Adverse Wastewater disposal/assimilation
Adverse Bilge purging/cleaning
REFERENCES FOR BENEFICIAL MANAGEMENT PRACTICES - 01
REFERENCES FOR ADVERSE MANAGEMENT PRACTICES - 01
COMMENTS ON MANAGEMENT PRACTICES -
Factors Influencing Populations: Sea otters prefer to feed in areas where
Pacific gaper densities are high and composed of small individuals unable to
burrow deeply because of sediment charactersistics; large Pacific gapers in
soft sediments are resistant to sea otter predation. The Pacific gaper may
compete with T. capax, however T. capax is more common in gravel-shell soils
whereas T. nuttallii is more common in pure sand substrates. The Pacific
gaper also burrows deeper than T. capax and thus avoids temporary freezing
conditions. No information is available concerning mortality rates, but very
high mortality rates probably occur during larval and early juvenile stages,
becoming lower as clams mature. Annual juvenile recruitment varies widely
and probably has a major effect on the population structure.*01*
Management Practices - 1 (DRAFT) - References
Species Pacific gaper
Species Id M060014
Date 26 AUG 96
References
01 Emmett, R. L., S. L. Stone, S. A. Hinton, and M. E. Monaco. 1991
Distribution and abundance of fishes and invertebrates in west coast
estuaries, Volume II: species life history summaries. ELMR Rep. No. 8.
NOAA/NOS Strategic Environmental Asessments Division, Rockville, MD,
329p.
References - 1