(DRAFT) - Taxonomy
Species clam, Pacific geoduck
Species Id M060190
Date 26 AUG 96
TAXONOMY
NAME - clam, Pacific geoduck
OTHER COMMON NAMES - Pacific geoduck clam
ELEMENT CODE -
CATEGORY - Aquatic Molluscs
PHYLUM AND SUBPHYLUM - ,
CLASS AND SUBCLASS - Bivalvia (Pelecypoda),
ORDER AND SUBORDER - Myoida,
FAMILY AND SUBFAMILY - Hiatellidae,
GENUS AND SUBGENUS - Panopea,
SPECIES AND SSP - abrupta,
SCIENTIFIC NAME - Panopea abrupta
AUTHORITY - Conrad, 1849
TAXONOMY REFERENCES - 236
COMMENTS ON TAXONOMY -
Superfamily--Hiatellacea
Taxonomy - 1 (DRAFT) - Status
Species clam, Pacific geoduck
Species Id M060190
Date 26 AUG 96
STATUS
Coded Status
Game (Consumptive Recreational)
Commercial
Commercial/consumption
REFERENCES FOR STATUS - 236
COMMENTS ON STATUS -
Geoduck clams dominate the biomass of benthic infaunal communities in many
parts of Puget Sound and support the most valuable commercial clam fishery
along the Pacific Coast of North America. From 1975 to 1987 the annual
catch from Puget Sound has remained between 1100 and 3900 t (2.4-8.6 million
lb) and landings in British Columbia have recently exceeded 5000 t/yr.*236*
The commercial fishery in Puget Sound is co-managed by the Washington
Department of Fisheries and Washington Department of Natural Resources.
These agencies lease subtidal geoduck clam tracts to commercial divers who
take the clams one at a time, using a water jet to loosen the clams from the
substrate. A significant portion of the catch is frozen and exported to
Japan, but there is a growing domestic market for the whole, live clams.
Large, light-colored geoduck clams (good quality) are in high demand in the
market compared to small, dark ones. Quality is inversely related to the
age of the clam and the water depth at which the clam was growing.*236*
Status - 1 (DRAFT) - Distribution
Species clam, Pacific geoduck
Species Id M060190
Date 26 AUG 96
DISTRIBUTION
Distribution - 1 HABITAT ASSOCIATIONS
HABITAT - MARINE
REFERENCES FOR HABITAT - 236
LAND USE -
Bays and Estuaries
REFERENCES FOR LAND USE - 236
NATIONAL WETLAND INVENTORY CODES
NWI NWICLS NWIMOD NWISPEC
Marine, subtidal FL2 L
Marine, intertidal FL2 L
REFERENCES FOR NWI - 236
COMMENTS ON HABITAT ASSOCIATIONS -
Lower intertidal and subtidal to depths of over 110 m along the west coast
of North America.*236*
Geoduck density is highest in substrates of mud-sand or sand compared to
mud or pea gravel or gravel substrates.*236*
Habitat Associations - 1 (DRAFT) - Food Habits
Species clam, Pacific geoduck
Species Id M060190
Date 26 AUG 96
FOOD HABITS
TROPHIC LEVEL -
FILTERER
REFERENCES FOR TROPHIC LEVEL - 236
LIFESTAGE FOOD FOOD PART
Adult Phytoplankton Not Applicable
Adult Bacteria Not Applicable
Adult Plankton Not Applicable
REFERENCES FOR GENERAL FOOD - 236
REFERENCES FOR ADULT FOOD - 236
COMMENTS ON FOOD -
Studies of the food habits of geoduck clam larvae, juveniles, and adults
have not been published; however, some information is available from casual
observations of gut contents of adults and from hatchery operations at the
Point Whitney Shellfish Laboratory. Geoduck clam larvae, juveniles, and
adults, like these stages in other clam species, feed by filtering food
particles from seawater with their gills. Microscopic examination of wet
smears of gut contents from adults taken from Puget Sound have shown only
phytoplankton. Geoduck clams live in water as deep as 110 m, which is well
below the photic zone. Clams below this zone probably feed on live
phytoplankton carried by wind-driven or tidal currents or dead plankton and
bacteria called marine snow, which settles from the photic zone.*236*
COMMENTS ON ADULT FOOD -
Studies of the food habits of geoduck clam larvae, juveniles, and adults
have not been published; however, some information is available from casual
observations of gut contents of adults and from hatchery operations at the
Point Whitney Shellfish Laboratory. Geoduck clam larvae, juveniles, and
adults, like these stages in other clam species, feed by filtering food
particles from seawater with their gills. Microscopic examination of wet
smears of gut contents from adults taken from Puget Sound have shown only
phytoplankton. Geoduck clams live in water as deep as 110 m, which is well
below the photic zone. Clams below this zone probably feed on live
phytoplankton carried by wind-driven or tidal currents or dead plankton and
bacteria called marine snow, which settles from the photic zone.*236*
Food Habits - 1 (DRAFT) - Environment Associations
Species clam, Pacific geoduck
Species Id M060190
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
E Water Temperature: Below 15 degrees C
L Water Temperature: Below 15 degrees C
L Water Temperature: Specified in Comments
J Water Temperature: Specified in Comments
A Water Temperature: Between 15-21 degrees C
A Water Temperature: Below 15 degrees C
G Bottom Type [Aquatic]: Mud or silt
G Bottom Type [Aquatic]: Sand
G Bottom Type [Aquatic]: Gravel
G Water Depth Preference: 50-100 ft.
E Relation to Substrate: Unattached - normally free living
L Relation to Substrate: Unattached - normally free living
J Relation to Substrate: Attached - normally sessile
A Relation to Substrate: Attached - normally sessile
G Currents: tidal
REFERENCES FOR ENVIRONMENTAL ASSOC_ - 236
REFERENCES FOR ADULT ENVIRONMENTAL ASSOC_ - 236
REFERENCES FOR JUVENILE ENVIRONMENTAL ASSOC_ - 236
REFERENCES FOR LARVAE ENVIRONMENTAL ASSOC_ - 236
REFERENCES FOR EGG ENVIRONMENTAL ASSOC_ - 236
COMMENTS ON ENVIRONMENTAL ASSOCIATIONS -
The only published data on salinity and temperature requirements are from
Goodwin. In this study, newly fertilized eggs were allowed to develop to
the straight-hinge stage in various combinations of salinity and
temperature. For 70% or more of the embryos to develop into normal
straight-hinge larvae the salinities had to remain between 27.5 and 32.5
ppt and the temperatures between 6 and 16 degrees C.*236*
Like many bivalves, the older life stages of geoduck clams can tolerate a
wider range of salinity and temperatures. Larvae beyond the straight-hinge
stage are routinely grown at the Point Whitney hatchery at water
temperatures up to 17 degrees C. Juveniles do well in water of 18 degrees
Environment Associations - 1 (DRAFT) - Environment Associations
Species clam, Pacific geoduck
Species Id M060190
Date 26 AUG 96
C. Adults in the lower intertidal and shallow subtidal zones of Quilcene
and Dabob Bays (Puget Sound) are exposed to water temperatures of 21-22
degrees C, sometimes for several days, during July and August in warm
years.*236*
Geoduck clams live in substrates of soft mud, sand, and pea gravel or
gravel substrates or mixtures of these materials. As mentioned earlier,
they grow larger in mud and sand or sand than in mud or pea gravel and
gravel. Densities are greatest in mud and sand or sand and lowest in
mud.*236*
COMMENTS ON ADULT ENVIRONMENTAL ASSOC_ -
Adults in the lower intertidal and shallow subtidal zones of Quilcene
and Dabob Bays (Puget Sound) are exposed to water temperatures of 21-22
degrees C, sometimes for several days, during July and August in warm
years.*236*
COMMENTS ON JUVENILE ENVIRONMENTAL ASSOC_ -
Juveniles do well in water of 18 degrees C.*236*
COMMENTS ON LARVAE ENVIRONMENTAL ASSOC_ -
Like many bivalves, the older life stages of geoduck clams can tolerate a
wider range of salinity and temperatures. Larvae beyond the straight-hinge
stage are routinely grown at the Point Whitney hatchery at water
temperatures up to 17 degrees C.
COMMENTS ON EGG ENVIRONMENTAL ASSOC_ -
The only published data on salinity and temperature requirements are from
Goodwin. In this study, newly fertilized eggs were allowed to develop to
the straight-hinge stage in various combinations of salinity and
temperature. For 70% or more of the embryos to develop into normal
straight-hinge larvae the salinities had to remain between 27.5 and 32.5
ppt and the temperatures between 6 and 16 degrees C.*236*
Environment Associations - 2 (DRAFT) - Life History
Species clam, Pacific geoduck
Species Id M060190
Date 26 AUG 96
LIFE HISTORY
MORPHOLOGY: The geoduck clam is one of the largest burrowing clams in the
world, attaining a shell length of at least 212 mm and a live weight
(including shell) of 3.25 kg. It gapes so widely (except at the hinge) that
the long, fused siphons and large mantle cannot be completely withdrawn into
the shell. In buried adults the extremely long, contractile siphon may
extend 1 m to reach the surface of the seabed. Siphonal openings are not
ringed with tentacles except in early post-larval stages. The tips of the
siphons lack the cutaneous plates found in the horse clams.*236* Small
juveniles have a large, well-developed foot, which becomes proportionally
smaller as the clam grows. The foot of an adult is so small that the clam,
if placed on its side, is not capable of righting itself and digging into
the substrate. The fused mantle is large and fleshy and has only a small
slit for the pedal gape.*236* The shell of an adult clam is quadrate and has
a thin, light brown periostracum. Shell sculpture and thickness vary from
fine and thin to rugose and thick. Studies have demonstrated that geoduck
clam shell is so highly variable in shape that it is difficult to quantify
by the traditional measurements of height, length, width, and
thickness.*236* The hinge has one large cardinal tooth in each valve. The
tooth on the left valve is always largest. The pallial sinus mark on the
shell is very broad and the anterior and posterior adductors are similar in
size.*236*
REPRODUCTION: Geoduck clams follow a simple annual reproductive
cycle. Gametogenesis begins in September and clams spawn from March to July.
Males become sexually mature at younger ages than females; sperm can be
found in the gonads of some males during any month of the year.*236* Geoduck
clams have been successfully spawned in the laboratory. Spawning is
triggered primarily by an increase in water temperature and the addition of
cultured phytoplankton to the spawning tank. Laboratory spawning has
occurred at water temperatures of 8.5-16.0 degrees C (mostly 12-14 degrees
C). Spawning has occurred as early as January 10 and as late as July 5.
Females have huge ovaries that contain many millions of eggs; however, they
are dribble spawners, normally releasing only 1 to 2 million eggs (or less)
during each spawning event. The largest release observed from a single
female during one spawning episode was 20 million eggs.*236* In the
hatchery, spawning is triggered by holding the brood stock at 9-12 degrees
C, and then increasing the water temperature slightly while adding algal
cells to the influent water. A male normally spawns first which then
triggers spawning in other males and females. Usually relatively few females
release eggs during a spawning event. Individuals can be induced to spawn as
many as three or four times during one season. Clams from areas where water
temperatures are relatively high in summer, spawn earlier in the season than
those from cold water areas. Eggs and sperm are released into the water,
where fertilization occurs. Fertilized eggs are spheres about 80 micrometers
in diameter, which are slightly negatively bouyant in sea water of 14
degrees C and 29 ppt of salinity. Very weak water currents will keep the
eggs suspended.*236* Depending on a number of factors such as water
temperatures, health of the brood, and presence of chemical cues, the larval
stage in laboratory and hatchery-reared geoduck clams has ranged from 16 to
47 days. The minimum of 16 days has been observed in the laboratory at
temperatures of 16 degrees C. The maximum of 47 days was reported from early
Life History - 1 (DRAFT) - Life History
Species clam, Pacific geoduck
Species Id M060190
Date 26 AUG 96
laboratory studies at water temperatures of 14 degrees C. The larval period
was shortened to 30 days at 17.6 degrees C. Bacterial contamination and
overcrowding may have artificially delayed larval growth and metamorphosis
in the early laboratory studies. Larval mortalities were extremely high,
indicating problems with culture practices. The length of the larval period
in nature has not been studied.*236* The fertilized egg undergoes cell
division and develops into a top-shaped trochophore larva that has rows of
short, hair-like cilia for swimming. This stage of the life history of
geoduck clams has not been reported in the literature. Within 48 hours, the
larvae form a straight-hinged larva or prodissoconch I, and the shell is
about 110 micrometers long. When length reaches 165 micrometers, rounded
elevations called umbones appear at the hinge on each shell and the larvae
enter the prodissoconch II stage of development. This is the last
free-swimming stage in the clam's life history.*236*
BEHAVIOR: Geoduck clams pass through a distinctive post-larval stage called the dissoconch for 2-4
weeks. At a shell length of 350-400 micrometers, the animal loses its velum
and associated swimming ability, develops spines on the growing edge of the
shell, and starts to crawl with its newly developed foot. This
transformation to the dissoconch is called metamorphosis and is a critical
phase in the clam's life, marking a change of life-style from a planktonic
existence in the water column to an increasingly sedentary style on the
seabed. Metamorphosis may be delayed when the animals are stressed or
critical environmental cues are lacking.*236* Researchers have observed that
chemicals from the tubes of several polychaete worm species trigger
metamorphosis of competent geoduck clam larvae (larvae capable of
metamorphosis). These tubes commonly occur in habitats where adult geoduck
clams are abundant. Studies have suggested that the larvae are capable of
selecting certain habitats by metamorphosing in response to chemical cues
from those habitats.*236* Postlarvae are capable of actively crawling along
the surface of the seabed using the well-developed ciliated foot. They are
also capable of attaching themselves to the substrate with byssal threads
produced by an organ in the foot. On a sand substrate, the postlarva inserts
its foot into the sand and burrows down less than one shell length. (They
apparently do not burrow deeper because the siphons are not developed at
this stage.) During the process of burrowing, byssal threads are attached to
a number of sand grains, forming a sand anchor. After the byssal attachment,
the larvae often return to the seabed surface, remaining attached to the
sand anchor. In strong water currents, postlarvae often detach from the sand
anchor and form several long byssal threads that greatly increase drag, thus
forming a parachute that carries the postlarvae down current. Thus,
postlarvae can remain stationary, crawl short distances, or travel long
distances with their byssal parachutes.*236* When the shell length is
1.5-2.0 mm, the sipons have developed and the clams start to burrow into the
substrate, remaining buried with only the tips of the siphon exposed. At
this point the clams begin to take on the general morphology of adults but
are considered juveniles until sexually mature at an average length of 75
mm. Small juveniles, less than 8 mm long, are unlike adults in having a
shell that is less sharply quadrate; also they can almost completely
withdraw into the shell, actively dig, and are still capable of producing
byssal threads. Juveniles up to 5 mm long may use the byssal parachute for
movement, but not as effectively as it is used by smaller postlarvae.
Juveniles longer than 5 mm probably do not move to another location, but
Life History - 2 (DRAFT) - Life History
Species clam, Pacific geoduck
Species Id M060190
Date 26 AUG 96
Life History - 3 (DRAFT) - Life History
Species clam, Pacific geoduck
Species Id M060190
Date 26 AUG 96
simply bury themselves deeper into the substrate as they grow.*236*
Digging speed is inversely related to shell length. Hatchery-reared
juveniles placed in partly sand-filled beakers with seawater right
themselves and dig completely into the substrate. Juveniles averaging 5 mm
long take about 8 min to bury themselves, whereas 10 mm animals require 30
min. Burial depth is directly related to shell length and the length of the
siphon.*236*
Upon reaching maximum adult size, geoduck clams become poor diggers and are
completely sedentary. They contribute substantially to the biomass of
benthic communities in which they occur. Average abundance in Puget Sound
in sand and mud bottoms at water depths of 6-18 m is 1.7 clams/square meter.
The average whole wet weight is 872 g. Biomass in these areas averages
1,483 g/m and ranges up to 19,651 g/m.*236*
LIMITING FACTORS:
Predation on geoduck clams is probably similar to that on other clams or
invertebrates that release millions of eggs into the water. Mortality
rates are high at first, slow during the juvenile stage, and become very
low when the clams reach adult size. Planktonic larvae are probably eaten
by fish, other plankton, or suspension-feeding invertebrates. After
metamorphosis and assuming the benthic life style, the young postlarvae face
a new host of predators, including epibenthic fish (soles, flounders),
worms, snails, starfish, and crabs. Geoduck clams in the juvenile stage
have thin, fragile shells that do not fully enclose and protect the soft
body parts from predators. Young geoduck clams cannot leap as cockles do to
avoid predators.*236*
POPULATION ATTRIBUTES:
Studies have found size at sexual maturity of geoduck clams to be variable.
The smallest sexually mature clam studied was 45 mm long. Of the clams
sampled, 50% were mature at 75 mm and an estimated age of 3
years. Males generally mature at a smaller size and earlier age than
females. Ripe gonads have been found in geoduck clams as old as 107
years.*236*
The sex ratio of clams older than 10 years is 50:50. Males can be
distinguished from females only by a microscopic examination of the gonads.
No hermaphrodites have been found.*236*
Despite the high fecundity of geoduck clams, the recruitment of juveniles
into the population is very low. As in most bivalves, mortality during the
planktonic and early settlement phases is extremely high, decreasing as the
clams pass through each life stage. The annual mortality rate of adults is
very low: reported rates are 0.01-0.05. Survival of a juvenile or adult is
directly related to the depth that the clam digs into the substrate. Clams
are more susceptible to predators near the surface of the seabed. Once the
clam buries itself deeper than 60 cm, it is beyond the reach of virtually
all predators except man. Juvenile and adult clams can be accurately aged
from acetate peels of the hinge plate. Clams older than 100 years are
common, and the age of the oldest live clam collected in Puget Sound was 131
years. A study in British Columbia found similar age distributions and a
Life History - 4 (DRAFT) - Life History
Species clam, Pacific geoduck
Species Id M060190
Date 26 AUG 96
maximum age of 146 years.*236*
LIFE HISTORY CODES -
Display Site: Water
Gestation/Incubation Period: 3-4 weeks
Gestation/Incubation Period: 1-2 months
Average Number of Offspring/Reproductive Effort: Grea
REFERENCES FOR LIFE HISTORY- 236
Life History - 5 (DRAFT) - Management Practices
Species clam, Pacific geoduck
Species Id M060190
Date 26 AUG 96
MANAGEMENT PRACTICES
RESULT MANAGEMENT PRACTICE
Beneficial Stocking captive-reared wild-strain animals
Adverse Shoreline modification/development
Adverse
Existing Other management practices [specified in comments]
Existing Regulating harvest - setting bag/creel limits
Existing Regulating harvest - restricting weapons/gear use
Existing Regulating commercial harvest gear types
REFERENCES FOR BENEFICIAL MANAGEMENT PRACTICES - 236
REFERENCES FOR ADVERSE MANAGEMENT PRACTICES - 236
REFERENCES FOR EXISTING MANAGEMENT PRACTICES - 236
COMMENTS ON MANAGEMENT PRACTICES -
The Washington State Department of Fisheries is currently exploring the
feasibility of enhancing the commercial fishery by planting hatchery-reared
geoduck calm seed into fished-out beds.*236*
Domestic and industrial pollution in Puget Sound, which has increased with
the expanding human population of the region, has led to restrictions on
geoduck clam harvest in portions of the Sound. Marine construction projects
such as piers, jetties, marinas, and pipelines displace increasing amounts
of geoduck clam habitat every year; aquaculture projects are also rapidly
expanding and competing for space in geoduck clam habitat. Because geoduck
clams are sedentary, suspension feeders that are very long-lived, they are
particularly susceptible to the effects of pollution and habitat loss.*236*
Geoduck clams taken for sport must be dug with hand tools. The daily legal
limit is three per person. The total sport catch is low compared with the
commercial landings.*236*
The commercial fishery in Puget Sound is co-managed by the Washington
Department of Fisheries and Washington Department of Natural Resources.
These agencies lease subtidal geoduck clam tracts to commercial divers who
take the clams one at a time, using a water jet to loosen the clams from the
substrate.*236*
The Washington Departments of Fisheries and natural Resources are engaged
in a program to reseed the clam beds with hatchery reared seed as the beds
are fished out.*236*
Since 1979 the annual catch has been limited to the optimum sustained yield
by regualting the numbers and sizes of the geoduck clam tracts that are
leased each year.*236*
Management Practices - 1 (DRAFT) - References
Species clam, Pacific geoduck
Species Id M060190
Date 26 AUG 96
References
236 * Goodwin, C. Lynn, Bruce Pease. 1989. Species Profiles:
Life Histories and Environmental Requirements of Coastal fishes
and Invertebrates (Pacific Northwest)--Geoduck Clam. Species
Profiles Series 82(11.120) (ed.). U.S. Fish and Wildlife Service
Washington, DC:14.
References - 1