Overview:  The Olympia oyster ranges from Southeast Alaska to Baja California, and is the only oyster that is native to Washington.  Formerly abundant, the Olympia oyster was an important food source for many coastal Native American tribes.  Oysters usually inhabit low tidelands or estuaries that remain inundated with water during low tide, although they also can be found on the undersides of floats and on pilings.  Although this species seldom reaches more than an inch-and-a-half in diameter, its quality as a food source quickly led early settlers to take advantage of the abundant oyster stocks of Willapa Bay.  Throughout the 1850's and 1860's, schooners laden with Olympia oysters were travelling between Oysterville, WA, and San Francisco, heralding the start of a lucrative Pacific Northwest shellfish industry.  By 1870, overharvesting had already significantly depleted oyster stocks in both Willapa Bay and Puget Sound.  Water pollution was another factor that had, and continues to have, profound effects on oyster populations.  As filter-feeders, oysters take in huge quantities of seawater (about 20 - 30 quarts an hour), to extract phytoplankton.  However, any pollutants or pathogens that are present are also extracted and quickly become concentrated in the oyster's tissues.  Though oyster growers strove to maintain and enhance the water quality of the tidelands that sustained their oyster-beds, unregulated effluent from surrounding pulp and paper mills before the 1950's played a large part in the declines of the Olympic oyster.  To augment their ailing stocks, oystermen began importing the larger and faster-growing Japanese or Pacific oyster in large numbers, which soon displaced the Olympia oyster in their cultivated beds.  Non-native oyster-predators, such as the Japanese oyster drill (Ocenebra japonica), and a parasitic flatworm (Mytilicola orientalis) were accidentally introduced along with their hosts and exacerbated the Olympia oyster's decline.

In the southern Puget Sound region, Olympia oyster populations continue to be threatened by pollution from motorboats, pulp mills and wastewater discharge.  Additionally, silt from highway construction projects has smothered a large proportion of the oyster population in the more shallow areas.  Despite increases in some local oyster populations due to water quality improvements, Olympia oyster stocks in Washington have never reached pre-exploitation levels.  Currently, the Puget Sound Restoration Fund is looking to re-introduce Olympia oysters in at least seven different sites throughout Puget Sound and Hood Canal.  To find out more about Olympic oysters in the Pacific Northwest, check out National Wetlands Research Center at http://www.nwrc.gov/publications/specindex.html#L.

Distribution: The Olympia oyster inhabits estuaries, small streams and rivers from southeast Alaska south to Baja California.