Geoduck aquaculture or geoduck farming is the practice of cultivating geoducks (specifically the Pacific geoduck, Panopea generosa) for human consumption. The geoduck is a large edible saltwater clam, a marine bivalve mollusk, that is native to the Pacific Northwest.
Juvenile geoducks are planted or seeded on the ocean floor or substrate within the soft intertidal and subtidal zones, then harvested five to seven years later when they have reached marketable size (about 1 kg or 2.2 lbs). They are native to the Pacific region and are found from Baja California, through the Pacific Northwest and Southern Alaska.
Most geoducks are harvested from the wild, but because of state government-instituted limits on the amount that can be harvested, the need to grow geoducks in farms to meet an increasing demand has led to the growth of the geoduck aquaculture industry, particularly in Puget Sound, Washington. Geoduck meat is a prized delicacy in Asian cuisine; the majority of exports are sent to China (Shanghai, Shenzhen, Guangzhou, Beijing, are the main Chinese markets), Hong Kong and Japan.
History Washington state Wild geoducks had been harvested in Puget Sound, Washington by residents and visitors for hundreds of years, but it was not until 1970 that the Washington Department of Natural Resources (WDNR) auctioned off the first right to commercially harvest wild geoducks. Research into the viability of farming geoducks began in the 1970s. In 1991, the development of hatchery and grow-out methods from brood stock were initiated. By 1996, commercial aquaculture had begun. As of 2011, there were 237 commercial sites operating on of privately owned properties (including those leased from other private owners). Commercial geoduck aquaculture has been primarily undertaken within the intertidal zone.
British Columbia Commercial harvesting of wild geoducks began in 1976. In the early 1990s, the cultivation method developed in Washington was adopted in British Columbia by Fan Seafoods Ltd and the Underwater Harvesters Association (UHA), a group of 55 licence holders for geoduck and horse clam fishery. The UHA used this method to initiate a wild geoduck enhancement program by seeding depleted subtidal areas with cultivated juvenile geoducks thereby ensuring continued supply in the wild. It even invented a mechanical seeder that plants cultured juvenile geoducks on subtidal beds. Through a collaboration agreement between the provincial government's Department of Fisheries and Oceans (DFO), Fan Seafoods Ltd. and UHA, five pilot sites were selected in 1996 to study the feasibility of a geoduck aquaculture venture. In 2007, the provincial government of B.C. licensed UHA to operate the first commercial geoduck farm on off Hernando Island.
Other areas No geoduck aquaculture industry exists in Southern Alaska and Mexico. In New Zealand, Cawthron recently reported successful attempts at rearing juvenile geoducks. The plan is to plant them in subtidal areas in order to supplement wild geoduck harvest.
Geoduck species and their distribution Panopea generosa is the geoduck species that is found in the Pacific Northwest and Alaska. Panopea globosa, which is another species in the same genus, Panopea, is harvested in Mexico's Gulf of California.
A small wild geoduck fishery exists in New Zealand for Panopea zelandica, the "deepwater clam", and in Argentina for Panopea abbreviata, the "southern geoduck". A fifth species, Panopea japonica, the Japanese geoduck, is found in Korea and Japan, but there is no viable commercial industry in those countries for this species.
Biomass densities in Southeast Alaska are estimated by divers then inflated by twenty percent to account for geoducks not visible at the time of survey. This estimate is used to predict the two percent allowed for commercial harvesting.
Predators and diseases Juvenile geoducks are susceptible to attack from predators in their first year when they have not yet burrowed deeply into the substrate. Crabs, sea stars, predatory gastropods, and flatfishes have been observed to feed on them. Adult geoducks, which are already buried deep in the substrate, are out of reach of most predators except for sea otters and humans.
In 2012, no infectious diseases had been observed attacking cultured juvenile geoducks planted in the wild up to that point. Surface abnormalities were observed in wild adult geoducks, but the pathogen or pathogens could not be identified. However, a protozoan parasite (Isonema sp) was believed to be the causal agent of cultured geoduck larvae mortalities at a Washington experimental hatchery.Kent, M.L., R.A. Elston, T.A. Nerad and T.K. Sawyer. 1987. An Isonema-like flagellate (Protozoa: Mastigophora) infection in larval geoduck clams, Panope abrupta. Journal of Invertebrate Pathology 50: 221229.
Production methods The Washington Department of Fisheries (WDF) Point Whitney Laboratory pioneered research into the aquaculture of geoducks in 1970. The initial purpose of developing the techniques was to enhance the wild population that was being depleted by commercial fishing. Their first challenge was inducing spawning from wild adult geoducks brought into the hatchery; the second challenge was the survival of the resulting larvae. As of 2012, research into improving culture techniques is continuing, however the basic environmental conditions for growth of geoducks have already been established.
Summary of optimal biophysical parameters for geoduck culture (nursery and grow-out)
Parameter Optimal Value Substrate mud/sand/pea gravel (penetration to 1m) Depth 3–20 m Temperature 8-18 C Salinity 26-31 ppt Transparency (Secchi) 2->10m Current velocity <1.5 kn (<0.75 cm/s) Productivity 15-200 mgC/m2/day
The techniques for culturing geoducks are similar to that of other bivalves. Modifications have been made by both academic and private laboratories through the years.
Collection of broodstock Geoducks spawn from spring to late summer in the wild, peaking in June and July. Because of this timing, an equal number of male and female clams are collected starting in the early fall when gametogenesis commences. The clams are placed in milk crates and maintained in polyethylene fish totes supplied with flowing seawater (10-12 °C) for several weeks. Microalgae is added as feed and regular cleaning is carried out to remove biodeposits.
Spawning method Spawning is initiated by changing the seawater and increasing the amount of microalgae to increase the temperature of the water. The higher temperature and abundant supply of microalgal feed induces spawning in males first, then in females.
Rearing of larvae Fertilized geoduck eggs remain floating in the water column for 16 to 35 days until they metamorphose and settle on the substrate. As larvae, they are kept at a water temperature of 16 °C and supplied with microalgal feed with frequent water changes.
Growing-out method Larvae that are ready to metamorphose are collected and placed in a primary nursery system where water temperature is kept at 15-17 °C and supplied with microalgal feed. Metamorphosed larvae are characterized by the development of an attachment mechanism known as byssal threads.
Once byssal threads have developed, the clams are moved to a secondary nursery system which contains sand as the substrate. They are kept here until they are large enough to be moved outdoors.
Tertiary nursery systems are made of large outdoor tanks or totes which have the same sand substrate and flowing seawater. The clams are kept in these systems until they reach a valve length of 5 mm, at which point they are ready to be planted.
Planting and seeding Four to five juvenile geoducks are planted inside PVC tubes that are "wiggled" into the sandy substrate along the intertidal zone during low tide. The PVC tubes are between 5 and 15 cm in diameter, with lengths from 20 to 30 cm, about 7 cm of which remain above the substrate. The plastic tubes are covered with a mesh net to protect the clams from predators. The tubes also serve to retain seawater at low tide, which prevents dehydration of the clams. After one to two growing seasons when the juvenile geoducks have burrowed themselves deep enough into the substrate to be out of reach of predators, the PVC tubes are removed. Not all tidelands are suitable for geoduck aquaculture. The sand must be deep and clean, and the water must have the right salinity and degree of cleanliness.
In Washington State, the aquaculture of geoducks occurs on intertidal lands, whereas in British Columbia, geoducks are cultured in subtidal areas, which necessitates the growing of juvenile geoducks to at least 12 mm instead of 5 mm before planting. Once planted in the subtidal bed, the area is covered with netting to protect the clams from predators (PVC tubes are not stable in subtidal beds due to strong currents).
Harvesting Mature geoducks are left to grow out until they are large enough to be marketable (1.0 kg). This can take from five to seven years. Wild and cultured geoducks are harvested by first loosening the substrate around them using a powerful nozzle that ejects high-pressured water. Once loosened, the clams are collected by hand and placed in crates for transport to a processing facility.
Grading and packing Although there is no standard grading system for quality, the color of the siphon (the whiter the better) and the size (up to 1 kg) are the main determiners of price. Live geoducks are packed in coolers and shipped on the same day they are harvested.
Economic importance The geoduck industry produces an estimated 6000 metric tons of clams annually, of which only about 10-13% come from aquaculture. Washington is the largest producer of wild and cultured geoducks.
Average Annual Production 2007-2010 Location Production (in metric tons) Wild Washington State 2143 British Columbia 1572 Mexico 1094 Culture Washington State 591 British Columbia 75 Total 5823
Difference between wild and cultured geoduck Wild Culture crunchier generally whiter hardier, travels better more uniform size less water shrinkage thinner shell may weigh 25% less than average wild geoduck
Major markets China (Mainland and Hong Kong) is where 95% of geoducks exports are sent. Although the clams are priced at about $20 per pound at the point of origin, they can sell for $100 to $150 per pound at their destination. While exports to Japan have decreased in recent years because of increasing prices, the market in China is expected to soar.
Management of the industry
British Columbia Environmental groups and citizens of British Columbia have voiced their concerns about geoduck aquaculture operations in the Province, even though the industry is still in its preliminary stages. Their main issue has been the lack of peer-reviewed studies on the impact geoduck aquaculture practices will have on the environment. Most concerned groups point to the situation in Puget Sound, Washington as an example of the environmental harm posed by geoduck farms. Other concerns being raised include the destruction of the natural aquatic habitat, washed up waste (such as nets), disease outbreaks, competition with wild species, and "purge fishing" or the removable of all wild geoducks in a specific area prior to the planting of cultured geoducks. This procedure is apparently necessary because of the economics of the industry.
The management of Canada's aquaculture sector is headed by the Department of Fisheries and Oceans. The department shares this responsibility with 17 other departments and agencies at the federal and provincial levels.