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Status of the European Green Crab in Oregon Estuaries in 2004

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  • Prepared for the Pacific States Marine Fisheries Commission and the Alaska Department of Fish of Game.
  • The recent invasion of Pacific Northwest estuaries by the European green crab, Carcinus maenas, caused much initial alarm. Following the last El Niño of 1997-98, a strong cohort of young green crabs appeared in estuaries along the coasts of Oregon, Washington, and as far north as Port Eliza on the west coast of Vancouver Island, British Columbia. Unusually strong northward-moving coastal currents (up to 50 km/day from September 1997 to April 1998) must have transported green crab larvae from more established source populations in California to the Northwest. Coastal transport events and recruitment of young green crabs have been much weaker in recent years. It was hoped that green crabs would go extinct in the Pacific Northwest estuaries once the original colonists reached the end of their life span of 4-6 years. This has not happened. Some recruitment has occurred every year since 1998. Recruitment strength appears to be linked to winter temperatures: cold winters (2002) result in poor recruitment while warm winters (2003), in good recruitment. Circumstantial evidence suggests that Coos, Yaquina, Netarts and Tillamook estuaries in Oregon and Willapa Bay, Washington harbor a small self-sustaining population of green crabs that is not dependent on a larval source from California. There can be a substantial time lag between the discovery of an exotic species and its impact on the native community. For example, green crabs were documented to exist in New England in 1817, but it was not until the 1950’s when this species expanded its range and increased in abundance sufficiently to impact the soft-shelled clam populations in Massachusetts, Maine and Nova Scotia. Even though green crab abundance in the Pacific Northwest is low when compared to Europe, eastern North America, Tasmania and California, it is imperative to continue monitoring efforts for two reasons: 1) to elucidate the process of range expansion of this model non-indigenous marine species with planktonic larvae and 2) to understand the role of ocean conditions on recruitment in order to predict the next strong recruitment event of green crabs.
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