The white-clawed crayfish (Austropotamobius pallipes) is the UK's only native crayfish species and one of its most critically endangered freshwater invertebrates. Devastated by crayfish plague (a water mould disease introduced with North American signal crayfish) and competition from signal crayfish, white-clawed populations have collapsed across most of their former range.
White-clawed crayfish are protected under Schedule 5 of the Wildlife and Countryside Act 1981 and are a priority species under the UK Biodiversity Action Plan. Population surveys show decline of over 90% in many areas since signal crayfish were introduced in the 1970s. Surviving populations are largely restricted to isolated headwater streams where signal crayfish have not yet arrived.
Crayfish plague (Aphanomyces astaci) kills white-clawed crayfish within days of exposure — North American species are immune carriers but white-clawed crayfish have no resistance. Mortality during plague events is essentially 100%, making biosecurity (preventing movement of water and equipment between sites) the most critical welfare intervention. Anglers, canoeists, and water managers are key vectors for plague spread.
Ark site programs — establishing captive and isolated wild populations in plague-free streams — preserve genetic diversity for future reintroduction. Captive breeding programs in specialist facilities maintain populations while habitat and management solutions are developed. Public engagement programs train water users in biosecurity protocols — check, clean, dry — to prevent plague spread.
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