Abstract

Since the mid-1970s signal crayfish (Pacifastacus leniusculus) have been introduced into Britain and spread to over 250 potential producers. Only 38 producers were registered in 1986 but this rose to 62 in 1989. However, production is still less than 10 tonnes per annum. Customs figures indicate an import and export trade in 'crayfish' but the true situation is not clear. Most signal producers are situated in southern England and it is in this area that crayfish plague has struck a number of native crayfish (Austropotamobius pallipes) populations since the early 1980s. Some 57% of recorded native crayfish sites in England and Wales are now in river catchments that have been affected by crayfish plague between 1980 and 1990. Signal crayfish are a proven vector of this disease in Britain, although other modes of transmission are possible. Many signal populations have developed in the wild, often close to signal production sites. The expansion of such populations can be very rapid under suitable conditions. Laboratory and in situ cage experiments indicate that plague-free signals are capable of eliminating native crayfish when at high densities, although in a number of locations they currently occur in the same habitat. Although the slender-clawed crayfish (Astacus leptodactylus) has been imported into Britain since the early 1970s, largely for the restaurant trade, few attempts have been to cultivate them. A number of wild populations have developed and, like the signals, have undergone rapid expansion in recent years. Recommendations are outlined for the conservation of the native crayfish in Britain.

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