Abstract

The American signal crayfish Pacifastacus leniusculus was introduced to Great Britain for aquaculture in the mid-1970s and has spread naturally and by human introduction, with corresponding losses of indigenous white-clawed crayfish, Austropotamobius pallipes, from crayfish plague and competition. At least five other crayfish species have been introduced illegally and are now established. Further releases of three species were banned (1992), keeping of crayfish was regulated (1996), and crayfish were banned as angling bait (2005). Despite legislation, introductions still occur and the introduced crayfish species continue to spread. Species risk assessments have recently been carried out for five non-indigenous crayfish species using a standardised methodology. This study describes the findings. Pathways and potential for spread differ between species, but all involve human action. Importation of live crayfish for food, a growing interest in the wild-harvest of signal and narrow-clawed crayfish, Astacus leptodactylus, translocations by the public (e.g., anglers), and the illegal trade in aquarium species were assessed as significant risks. All the non-indigenous crayfish have potential for harm, but the risks from two European species, the noble crayfish, Astacus astacus, and the narrow-clawed crayfish, A. leptodactylus, were considered minor, compared to those of signal crayfish, spiny-cheek crayfish, Orconectes limosus, virile crayfish, Orconectes virilis, (yet to be risk-assessed) and red swamp crayfish, Procambarus clarkii. Future trends in the colonisation of Great Britain are considered.

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