Austropotamobius pallipes


Austropotamobius pallipes is an endangered European freshwater crayfish, and the only species of crayfish native to the British Isles. Its common names include white-clawed crayfish and Atlantic stream crayfish.

Distribution and ecology

It 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. A. pallipes is the only species of crayfish found in Ireland, occurring over limestone areas inhabiting rivers, streams, canals, and lakes. It is absent from the more acidic waters of the west, and occurs in streams with a moderate flow alongside other freshwater invertebrates such as caddis fly, mayfly, and mollusc species. Trout and three-spined stickleback also occur in the same habitat. Tree roots and rocks in the banks provide shelter. Juveniles shelter in vegetation such as watercress and grass mats growing out of the bank.

Description

A. pallipes is an olive-brown colour, with pale-coloured undersides to the claws. It may grow to long, although sizes below are more common. It typically lives in rivers and streams about 1 metre deep, where it hides among rocks and submerged logs, emerging to forage for food, and also in lakes.

Conservation

In France A. pallipes is found in streams such as the Mornante and Sellon, two small tributaries of the Dorlay in the Loire department. It is protected as a heritage species.
The distribution of A. pallipes is rapidly shrinking and in Great Britain it is now more or less restricted to central and northern England, east Kent, and eastern Wales and a population has been discovered in Essex. There is also a population in Candover Brook, a tributary of the River Itchen in Hampshire. Until recently a population had existed in the River Frome in Bristol/South Gloucestershire, but Avon Wildlife Trust believe this was wiped out during 2007–2008. Populations of A. pallipes can also be found in the upper reaches of the River Thames, where it competes with the introduced noble crayfish. Dowdeswell Reservoir in Gloucestershire supports A. pallipes and during the engineering works undertaken in 1998, Severn Trent put in place a management programme for its protection. However, it was once found across most of England and Wales.
One of the major reasons for this decline is the introduction of the invasive North American signal crayfish and red swamp crayfish. The signal crayfish is a carrier of crayfish plague, an infectious disease to which it has resistance, while A. pallipes has none. A. pallipes is also sensitive to many kinds of pollution, such as insecticides.