The white-clawed crayfish Austropotamobius pallipes lives in a diverse variety of clean aquatic habitats but especially favours hard-water streams and rivers. A major threat to the native white-clawed crayfish is posed by the introduction of non-native species of crayfish, which have been farmed in Britain since the late 1970s. Soon after this, crayfish plague (a virulent disease caused by the fungus Aphanomyces astaci) broke out and spread rapidly, causing drastic losses of native crayfish in rivers in England. It is believed that this disease was introduced and is spread by the most frequently farmed species, the North American signal crayfish Pacifastacus leniusculus, a carrier of the disease. Crayfish plague can be introduced into a waterbody not only by entry of signal crayfish but also by water, fish or equipment that has been in contact with signals. This greatly increases the risk to remaining white-clawed crayfish populations.
Signal and other non-native crayfish are larger and more aggressive than the native species and are able to produce more young. Consequently, the introduced species pose a threat not only because some are disease-carriers, but also through predation and competition with white-clawed crayfish. In Britain, signal crayfish are now well-established in the wild. In Northern Ireland no crayfish farms have been established and crayfish plague is unknown, although it occurs in the Republic of Ireland (Holdich & Reeve 1991; Holdich & Rogers 1997). It is only in areas free of disease that white-clawed crayfish are likely to survive in the future.
European status and distribution
A significant part of the EU resource is found in the UK and the Republic of Ireland, where is widespread.
Austropotamobius pallipes is widespread in most parts of England and is common in parts of eastern Wales. It is present in south-west Northern Ireland. A significant part of the EU resource is found in the UK, but the species is now seriously threatened over most of its range in Britain.
Craven in northern England supports strong populations of white-clawed crayfish Austropotamobius pallipes in the limestone streams feeding Malham Tarn, and in Malham Tarn itself. This site is well-isolated and is therefore an important refuge, unlikely to be invaded by non-native crayfish species.
This lowland site in central England represents white-clawed crayfish Austropotamobius pallipes in standing water. This 1 ha marl pit holds a very large population, estimated at 50,000. Although crayfish plague outbreaks have occurred in the Midlands, this waterbody is isolated from river systems and is a good example of a ‘refuge’ site in an important part of the species’ former range.
These four marl loughs in Northern Ireland have strong isolated populations of white-clawed crayfish Austropotamobius pallipes. This site has been selected because of its hydrological isolation and the absence of crayfish plague from Northern Ireland.
Cumbria, North Yorkshire, Northumberland and Tyne and Wear
The Eden is a river with high water quality that supports a large population of white-clawed crayfish Austropotamobius pallipes in the northern part of its range in England. As with the River Wye, the tributaries of the Eden, especially those flowing off limestone, are of particular importance.
The Kent is a river of upland character in southern Cumbria. Densities of white-clawed crayfish Austropotamobius pallipes are very high throughout much of the Kent system (particularly in the tributaries), perhaps higher than anywhere else in England.
The Wensum is a chalk-fed river in eastern England, and is an eastern example of riverine white-clawed crayfish Austropotamobius pallipes populations. As with most of the remaining crayfish populations in the south and east of England, the threats from non-native crayfish species and crayfish plague are severe. Designation of the river as a SAC provides as much protection as can be afforded to such vulnerable populations.
East Wales, Gloucestershire, Wiltshire and Bristol/Bath area, Herefordshire, Worcestershire and Warwickshire, West Wales and The Valleys
The Welsh River Wye system is the best site known in Wales for white-clawed crayfish Austropotamobius pallipes. The tributaries are the main haven for the species, particularly at the confluences of the main river and the Edw, Dulas Brook, Sgithwen and Clettwr Brook.
SACs where this Annex II species is a qualifying feature, but not a primary reason for site selection