The North American signal crayfish, with particular reference to its success as an invasive species in Great Britain

In the last 50 years, at least eight non-indigenous crayfish species (NICS) have been introduced into Great Britain for a variety of purposes including aquaculture, fish markets, restaurants and the aquarium trade, and incidental introductions (for example with consignments of fish and plants), and all have established viable wild populations except one. However, at present, only the North American signal crayfish [Pacifastacus leniusculus (Dana 1852)] is causing notable ecological problems, mainly due to its invasive capabilities, its impact on freshwater communities (including salmonid fish) through its feeding habits and its role as an ecosystem engineer, its interference with angling activities, and the fact that it can act as a vector of crayfish plague, to which Great Britain's indigenous white-clawed crayfish is highly susceptible. The other four North American crayfish introduced into Great Britain are capable of similar negative impacts, but are nowhere near as widespread. It is estimated that the various activities set up to try and control and manage the signal crayfish and repair the damage caused by it cost Great Britain over £ 2 million per annum and are sure to increase as populations expand. Despite stringent legislation, the signal crayfish continues to be spread by illegal introductions as well as by natural expansion of range. The distribution and biology of signal crayfish and the reasons for its success in Great Britain are examined and discussed.