Geoduck Clam

Geoduck Clam
Latin Name

Panopea abrupta

Group Name

Molluscs

Taxonomy details

Habitat

Geoduck clams are found in the waters of the northeast Pacific from Alaska to Baja California. Living at variable depths from the low intertidal zone to more than 100 metres, they burrow into the ocean floor. A developing geoduck digs about a third of a metre per year. After reaching about a metre depth, the adult geoduck settles in for a long uneventful life.

Species Description

Geoduck clams are bivalves, and have two shells that are white and somewhat rectangular in shape. Their equal-sized valves do not conceal their enormous siphon (neck), which is white to reddish-brown in colour. Geoduck clams are the largest burrowing clams in the world, with a shell length that can exceed 20 centimetres. They generally weigh between 0.5 and 1.5 kilograms, but, occasionally, grow as large as 3 kilograms. Geoducks are slow-growing and long-lived, with maximum ages of at least 168 years.

The geoduck clam (Panopea abrupta) occurs from Alaska to the Gulf of California in the northeast Pacific, from the Intertidal zone to depths of at least 110 metres. It buries itself in up to a metre of sand, mud, gravel, and other soft substrates. The fishery occurs throughout coastal British Columbia and is conducted with HOOKA (surface-supply air) dive gear.

Geoduck Life Cycle

Geoducks ("gooey-duck") are harvested commercially by divers using high pressure water delivered through a nozzle (known as a "stinger") which loosens the substrate around the clam and allows the diver to lift the clams out live. Geoducks are quickly shipped to processing plants where they are packed and usually delivered live to Asian markets.

Geoducks are distributed from Alaska to the Gulf of California (Quayle 1970), however, commercial fisheries exist only in northern Washington State, throughout British Columbia and in Alaska. Geoducks are large burrowing clams found between the intertidal and approximately 210 m (Jamison et al. 1984), with an average landed weight of approximately one kilogram. Individuals can be aged from growth rings using a validated procedure (Shaul and Goodwin 1982). They are among the longest lived animals in the world, often reaching ages in excess of 100 years and with a maximum recorded age of 146 years (Breen and Shields 1983, Harbo et al. 1983). Geoducks grow rapidly in the initial 10 to 15 years, after which time the growth in shell length ceases while total weight increases at a slow rate through a thickening of the shell and an increase in meat weight (Harbo et al. 1983, Goodwin and Shaul 1984, Sloan and Robinson 1984). Estimates of natural mortality rate in British Columbia populations range from 0.01 to < 0.05 (Breen and Shields 1983, Harbo et al. 1983, Sloan and Robinson 1984, Noakes and Campbell 1992). Geoducks begin to recruit to the fishery at age 4 and are fully recruited at 12 years (Harbo et al. 1983).

Adult geoducks have separate sexes. Ripe gonads are found in clams ranging from 7 to 107 years old, suggesting that individuals may be capable of reproducing over a century. Spawning occurs annually, mostly from June to July in association with increases in seawater temperatures (Sloan and Robinson 1984). Females release from 7 to 10 million eggs which are fertilized and develop in the water column until settlement on the bottom within 40 to 50 days (Goodwin et al. 1979, Goodwin and Shaul 1984). The settled post-larvae are active crawlers and can travel along the bottom aided by a byssal thread parachute. At a shell length of approximately 2 mm, they begin to burrow into the substrate; the depth occupied is related to the shell length and siphon length. At settlement and for the first two years , juvenile geoducks are vulnerable to a number of predators, including snails, sea stars, crabs (Cancer spp), shrimp and fishes (Goodwin and Pease 1989). Fast growing clams can bury to a refuge of 60 cm or more in two years. The end of the burrowing stage coincides with the beginning of annual reproductive activity at 7 to 8 years for males and females, respectively (Sloan and Robinson 1984).

Despite the large reproductive output of P. abrupta over a long life, juveniles are scarce and recruitment appears to be low. Age-frequencies do, however, show peaks of juvenile abundance which suggests that populations may be supported by recruitment pulses. Laboratory experiments indicate that geoduck embryos have relatively narrow salinity and temperature tolerance limits (Goodwin 1973).

Stock Assessment

Illustration of a geoduck

Illustration of a geoduck

The management strategy employed in the geoduck fishery is harvest-rate based quotas over rotational fishing areas. Much of the scientific research that is conducted on geoducks is aimed at estimating the biomass of populations in commercially-harvested areas. SCUBA surveys provide the data to estimate the average density; mean individual geoduck weight is obtained from biological and market sampling; and geoduck bed area is estimated from fishery logbook information and from SCUBA and acoustic surveys. The product of these three variables is the estimated biomass. Quotas are derived using a harvest rate of 1.8% of biomass. To date, almost 50% of the measured geoduck bed area has been surveyed either by SCUBA or remote-sensing acoustic surveys, or both. Thus, the recommended commercial harvest amounts are increasingly based on information derived from data and less on conservative extrapolation. Quotas and harvest amounts are stable with no anticipation of change, barring that resulting from population declines due to sea otter (Enhydra lutris) predation.

In-season, the fishery is managed on a fine spatial scale, allowing qualitative information to be collected for most beds harvested, including density estimates and indicators of productivity. Current objectives in Science are to characterize the geoduck beds to allow for spatial analysis and a better understanding of the metapopulation dynamics.

Geoduck research at the Pacific Biological Station is co-funded by the Underwater Harvesters Association (UHA).

Geoduck Current Research

Transect Surveys

Map: Geoduck surveys in BC.

Geoduck surveys in BC.

Dive surveys of geoducks have been conducted in collaboration with the UHA and First Nations since 1992 in all areas of the BC coast. To date, approximately 70 individual surveys (10 to 15 days each) have been conducted, covering over 25% of the beds and over 50% of the total bed area that is available for commercial harvest. Surveys provide the density data required to estimate biomass, from which quotas are calculated.

The method used to survey involves laying lead-core transects, perpendicular to the shore, in random locations within known commercial beds. SCUBA divers swim on either side of the transect line with a 1-metre bar and count the number of geoducks and record associated habitat data between the transect line and the edge of the bar. The divers stop at the end of 5-metre marked sections to record their observations. For wide beds, every 2nd, 3rd or 4th quadrat is sampled, depending on the width. This allows more transects to be completed in a bed which reduces the variability in the data.

Biological sampling

At the end of transect surveying, a biological sample of approximately 450 geoducks is collected from three randomly-chosen sites within the survey area. The geoducks are harvested with no bias for size, tagged with unique numbers and shipped to a licensed processing plant where they are measured and weighed and the meats removed for sale.

The shells are sent to the Pacific Biological Station where the shells are further processed to determine the animal ages. Geoduck ages are obtained by counting the rings on a cross section of the shell in the area of the hinge. The biological sample provides information of age and size distribution of populations, recruitment trends and growth rates.

Photo: Survey divers with metre bars and clipboard with data sheets. Photo Dominique Bureau

Survey divers with metre bars and clipboard with data sheets. Photo: Dominique Bureau

Photo: Processing geoducks. Photo Claudia Hand

Processing geoducks. Photo: Claudia Hand

Photo: Processing geoducks. Photo Claudia Hand

Processing geoducks. Photo: Claudia Hand

Acoustical Seabed Classification

Photo: Cross-section of geoduck shell showing annual growth rings.

Cross-section of geoduck shell showing annual growth rings.

Since the geoduck clam is harvested from subtidal fine-grain sediments, this makes them a perfect candidate for acoustical substrate classification. Acoustical surveys are used to determine the sediment composition of the top layer of the seabed in order to map the distribution of substrates suitable for harvestable geoduck populations. To date, approximately 20% of geoduck beds and 40% of geoduck bed area have been acoustically surveyed.

Remote acoustical sensing is also useful for the design of biological field surveys. As well, spatial analysis with Geographic Information System (GIS) software provides the framework for studies of pre and post-fishery population distribution and abundance.

Geoduck Publications

Stock Status Report

Integrated Fisheries Management Plan

Horse Clam Publications

Integrated Fisheries Management Plans

Overview of the Fishery

Research documents and stock status reports - Scientific papers and short resource status papers, available through the Department's Canadian Science Advisory Secretariat (CSAS) site

Geoducks ("gooey-duck") are harvested commercially by divers using high pressure water delivered through a nozzle (known as a "stinger") which loosens the substrate around the clam and allows the diver to lift the clams out live. Geoducks are quickly shipped to processing plants where they are packed and usually delivered live to Asian markets.

The recreational fishery is limited to hand digging methods: Commercial gear ("stingers") cannot be used for sport harvest.

The commercial fishery is managed by limiting harvest with a combination of a total allowable catch, individual licence quotas and a catch verification program. The Total Allowable Catch (TAC) is calculated by first determining the biomass (the product of the bed area, the geoduck density and mean individual geoduck weight), and applying an annual harvest rate of 1.8%. Deductions from the TAC are made for clams harvested in scientific surveys, for geoduck broodstock for aquaculture and enhancement purposes and for biotoxin monitoring programs. The remaining TAC is divided into 55 equal quotas, one for each licence eligibility.

A three-year area rotational process is in effect in many areas of the coast. Each of the three geographic regions of the coast (North Coast, West Coast of Vancouver Island and Inside Waters), is divided into three sub-units with roughly equal geoduck harvest areas. Some of these sub-units are fished at three times the annual exploitation rate (a total harvest rate of 5.4 %) once every three years. The exceptions to rotational fisheries are in Areas 16 and 23 to 27 which are fished annually to increase flexibility in harvest management. Rotational fisheries concentrate the fishing fleet to make it easier to monitor quotas and reduce the annual number of landing ports for validation of landings. As well, they allows for a more thorough examination of fishery areas, since data from only one third of the coast needs to be processed.

There are circumstances where annual fisheries are more sensible such as on the West Coast of Vancouver Island where closures due to PSP and predation from Sea Otters require the flexibility of having annual access to all areas.

Contacts

Erin Wylie
Lead Resource Manager
Geoduck Fishery
250-756-7271
erin.wylie@dfo-mpo.gc.ca
Claudia Hand
Science
Nanaimo
250-756-7139
claudia.hand@dfo-mpo.gc.ca

For other geoduck fishery departmental contacts, please consult the Shellfish Contacts page.

For more information about ongoing research on the geoduck at the Pacific Biological Station, please contact:

Claudia Hand
 250-756-7139
 Claudia.Hand@dfo-mpo.gc.ca
Dominique Bureau
 250-756-7114
 Dominique.Bureau@dfo-mpo.gc.ca
Ian Murfitt
 250-756-7081
 Ian.Murfitt@dfo-mpo.gc.ca
Miriam O
 250-756-3365
 Miriam.O@dfo-mpo.gc.ca
Reziah Khan
 250-756-7156
 Reziah.Khan@dfo-mpo.gc.ca