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PACIFIC OYSTER

DID YOU KNOW? Pacific oysters were introduced from Japan. They develop first as males, and after a year begin to function as females.

SCIENTIFIC NAME: Crassostrea gigas.

COMMON NAMES: Japanese Oyster, Miyagi oyster, giant oyster, immigrant oyster, and giant Pacific oyster.

DESCRIPTION: Rough shell that is highly fluted and laminated. Shells are usually whitish with purple streaks and spots. Can reach 10 inches in length.

LIFECYCLE: The Pacific oyster is an exotic species, introduced into west coast estuaries from Japan. Because spawning depends on a rise in water temperatures above eighteen degrees Celsius, it only spawns erratically in west coast estuaries. As a result, cultured "spat" is used to seed oyster beds. When spawning does occur, it occurs primarily in July and August. Eggs and larvae are planktonic distributed throughout the water column in estuarine waters. Later stage larvae settle out of the water column and crawl on the bottom searching for suitable habitat before settling. Juveniles and adults are sedentary and are found in lower inter-tidal areas of estuaries. Oysters prefer firm bottoms, and usually attach to rocks, debris or other oyster shells. However, they can also be found on mud or mud-sand bottoms.

RANGE: In North America, the Pacific oyster is found from Southeast Alaska to Baja California. It is cultivated primarily on oyster farms in protected coastal estuaries; however, some wild beds exist in Washington and British Columbia.

HABITAT AND ECOLOGY: The Pacific oyster is a highly valuable estuarine species which is threatened by pollution in its environment because it concentrates contaminants. Presently, many estuarine areas are completely closed to oyster culture and harvest because of bacterial and chemical contamination associated with urban centers, marinas, and sewage outfalls. In fact, on any given day in the United States, one third of all shellfish beds are closed due to contamination. Oysters face many other threats as well. Antifouling paints containing copper can alter the growth of oysters as well as cause the shell to thicken and oxygen consumption to increase. The high sulfite content discharges by pulp mills in the Pacific Northwest are also known to reduce survival and growth of oysters. In addition, siltation and turbidity resulting from logging and onshore development can cause early larvae mortality. Dredging of estuaries has also severely restricted the areas available for successful production.

ECONOMIC VALUE: Introduced in the early 1900's from Japan, Pacific oysters quickly grabbed a foothold in North America's growing aquaculture industry. In fact, the Pacific oyster is Washington's most valuable shellfish resource. Important spawning beds are located in Puget Sound, Hood Canal, Grays Harbor, Tillamook Bay, Coos Bay and Morro Bay.


Revised 12/16/96