Technical Report

Status of the European Green Crab, Carcinus maenas, in Oregon and Washington coastal Estuaries. Report for 2020 and 2021

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  • The European green crab (Carcinus maenas) has persisted in Oregon and Washington coastal estuaries since the late 1990s. A strong year class arrived in the Davidson Current during the 1998 El Niño, but numbers decreased and remained below 1 per trap per day until the arrival of the 2015-2016 El Niño. Ocean indices indicate that California was the predominate source of larvae prior to the 2015-2016 El Niño (Behrens Yamada & Kosro, Behrens Yamada, Peterson & Kosro, 2015). Since then, numbers have increased steadily to an average of around 6 crabs per trap per day for Yaquina and Coos estuaries, with maximums of up to 25- 28 per trap. Measurable ecological impact is predicted to occur around 10 per trap (Grosholz et al. 2011). Between the two El Niños recruitment of young green crabs to these estuaries was sporadic with many years of recruitment failure. But since 2015 recruitment has been good every year. Since green crabs live for 6 years, these recent strong year classes can produce larvae until 2027. Evidence suggests that the Davidson Current transporting larvae from California during the winter is no longer the only source of larvae for our coastal estuaries (Behrens Yamada, Fisher and Kosro 2021). Now that populations in Oregon, Washington and British Columbia have built up, we have evidence for local production and for larvae sources from a genetically distinct population on Vancouver Island (Alan Shanks and Carolyn Tepolt, personal communication). The current cooler ocean conditions could hold recruitment in check, but a return to high PDO and strong El Niño patterns would signal good recruitment and higher green crab densities. Even though green crab abundance in Oregon and Washington is still low when compared to Europe, eastern North America, Tasmania, California and the west coast of Vancouver Island, it is imperative to continue monitoring efforts for two reasons: 1) To elucidate the process of range expansion and population persistence of European green crabs. It could serve as a model for the spread of other non-indigenous species with planktonic larvae. 2) To predict the arrival of strong year classes from ocean conditions and to alert managers and shellfish growers of possible increases in predation pressure from this invader.
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