Endangered Crustaceans - White clawed crayfish
The White-clawed Crayfish (Austropotamobius pallipes) is an endangered European freshwater crayfish and the only species of crayfish native to the British Isles. It is also known as the Atlantic stream crayfish. The White-clawed Crayfish is found from the Balkan Peninsula to Spain and reaches its northerly limit in Great Britain and Ireland, where it also has its greatest population density.
The White-clawed Crayfish is an olive-brown coloured crayfish, with pale coloured undersides to its claws.
The White-clawed Crayfish may grow to 12 centimetres (5 inches) long, although sizes below 10 centimetres are more common. The White-clawed Crayfish typically lives in rivers and streams about 1 metre deep, where it hides among rocks, submerged logs and lakes, emerging to forage for food.
The population of White-clawed Crayfish is rapidly declining and once found across most of England and Wales in Great Britain, it is now more or less restricted to central and northern England and eastern Wales.
There is a regionally significant population in the River Frome in South Gloucestershire and Bristol and a population has been discovered in Essex. There is also a population in Candover Brook, a tributary of the River Itchen in Hampshire.
One of the major reasons for this decline is the introduction of the invasive North American signal crayfish (Pacifastacus leniusculus). The signal crayfish is a carrier of crayfish plague, an infectious disease to which it has resistance while the native crayfish have none. The British species is also sensitive to many kinds of pollution, such as insecticides.
The White-clawed Crayfish is the only species of crayfish found in Ireland, occurring over limestone areas inhabiting rivers, streams, canals and lakes.
White-clawed Crayfish are absent from the more acidic waters of the west. They occur in streams with a moderate flow alongside other freshwater invertebrates such as caddis fly, mayfly and mollusc species.
Trout and 3 Spined Stickleback also occur in the same habitat. Tree roots, rocks in the banks provide shelter. Juvenile White-clawed Crayfish species shelter in vegetation such as watercress and grass mats growing out of the bank.
The White-clawed Crayfish is classed as 'Vulverable' on the IUCN list 10 May 2006.