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Research Document - 2008/042

Risk Assessment for European green crab (Carcinus maenas) in Canadian Waters

By T.W. Therriault, L.M. Herborg, A. Locke, and C.W. McKindsey


Non-indigenous species continue to be dispersed to new environments and it is important for managers to understand the potential risk posed by these species. The European green crab (Carcinus maenas) has a rather extensive invasion history dating back over a century in North America. In order to determine the potential risk posed by this non-indigenous crab species to Canadian waters, including both the Atlantic and Pacific coasts, a formal risk assessment was undertaken. Most global introductions of crabs have been attributed to commercial shipping activities. European green crab already exists in Canadian waters on both coasts with both attributed to human-mediated activities. Based on impacts of green crab elsewhere owing to their extensive invasion history, there is considerable concern about the potential ecological (biological, habitat) and genetic impacts if green crab spread in Canada. Life history characteristics of green crab enhance long-distance natural dispersal. Further dispersal via ballast water is probable but a number of other anthropogenic dispersal vectors exist.

Fisheries and Oceans Canada conducted a national risk assessment to determine the potential risk posed by European green crab in Canada. This assessment included evaluating the probability of arrival, survival, reproduction and spread and potential consequences to determine a risk level. In addition, the potential risk posed by pathogens, parasites or fellow travelers (e.g. other invasive species) also was determined. These components were assessed in an expert, peer-review workshop held during February 2008 using the best available information on their biology, potential vectors of introduction, and impacts in both native and introduced ranges. The assessment concluded that European green crab generally posed a moderate to high risk on both coasts depending on the ecological endpoint assessed. For pathogens, parasites or fellow travelers the risks were deemed low. However, as little is known about many potential pathogens, parasites and fellow travelers of this crab species there was considerable uncertainty.

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