The geoduck is native to the west coast of North America. The shell of the clam ranges from 15 centimetres (5.9 in) to over 20 centimetres (7.9 in) in length, but the extremely long siphons make the clam itself much longer than this: the “neck” or siphons alone can be 1 metre (3.3 ft) in length. The geoduck is both one of the largest clams in the world, and one of the longest-lived animals of any type.
These marine bivalve mollusks are the largest burrowing clams in the world, weighing in at an average of 0.68 kg (1½ pounds) at maturity, but specimens weighing over 6.8 kg (15 pounds) and as much as 2 metres (over 6½ ft) in length are not unheard of.
A related species, Panopea zelandica, is found in New Zealand and has been harvested commercially since 1989. The largest quantities have come from Golden Bay in the South Island where 100 tonnes were harvested in one year. There is a growing concern over the increase of parasites in the Puget Sound population of geoduck. Whether these microsporidium-like parasitic species were introduced by commercial farming is being studied by Sea Grant. Research to date does indicate their presence.
Geoducks are one of the longest-living organisms in the animal kingdom. The oldest recorded specimen was 168 years old, but individuals over 100 years old are rare. A geoduck sucks water containing plankton down through its long siphon, filters this for food and ejects its refuse out through a separate hole in the siphon. Adult geoducks have few natural predators, which may also contribute to their longevity. In Alaska, sea otters and dogfish have proved capable of dislodging geoducks; starfish also attack and feed on the exposed geoduck siphon.
Geoducks are broadcast spawners. A female geoduck produces about 5 billion eggs in her century-long lifespan—in comparison, a human female produces about 500 viable ova during the course of her life. However, due to a low rate of recruitment and a high rate of mortality for geoduck eggs, larvae and post-settled juveniles, populations are slow to rebound. In the Puget Sound, studies indicate that the recovery time for a harvested tract is 39 years.
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.
Alternate spellings include gweduc, gweduck, goeduck, and goiduck. It is sometimes known as the mud duck, king clam, or when translated literally from Chinese, the elephant-trunk clam.
The large, meaty siphon is prized for its savoury flavour and crunchy texture. Geoduck is regarded by some as an aphrodisiac because of its phallic shape. A team of American and Italian researchers analysed bivalves and found they were rich in amino acids that trigger increased levels of sex hormones. Their high zinc content aids the production of testosterone.
- It is very popular in China, where it is considered a delicacy, mostly eaten cooked in a fondue-style Chinese hot pot.
- In Korean cuisine, geoducks are eaten raw with spicy chilli sauce, sautéed, or in soups and stews.
- In Japan, geoduck is prepared as raw sashimi, dipped in soy sauce and wasabi. On Japanese menus in cheaper sushi restaurants, geoduck is sometimes substituted for Tresus keenae, a species of horse clam, and labeled mirugai or mirukuigai. It is considered to have a texture similar to an ark shell (known in Japanese as akagai). Mirugai is sometimes translated into English as “giant clam”, and it is distinguished from himejako sushi, which is made from Tridacna gigas.