Freshwater white-clawed crayfish  (Austropotamobius pallipes)

The only freshwater crayfish native to the UK (3), this species is olive-green to brown in colour and can reach up to 12 centimetres in length. The common name refers to the fact that the undersides of the claws are off-white to pinkish in colour. Females tend to have wider abdomens than males, and males have larger claws. In males, the first two appendages are specialised; they are used to place a sperm mass (spermatophore) underneath the female during mating (2).

This crayfish was once widely distributed across Europe, but has undergone a severe decline, and remaining populations are increasingly fragmented (2). Before 1980 this species was also widespread throughout Britain and Ireland (2), but a large number of populations have since been lost (3). It is currently still fairly abundant in central and northern areas of England (2).

Tends to prefer clear, well-oxygenated, alkaline water (2) and occurs in small streams, lakes, rivers, water-filled quarries and reservoirs (2).

This crayfish tends to be nocturnal, emerging at night to feed on a broad diet consisting of detritus, animal matter and plants. It also occasionally indulges in cannibalism, particularly on individuals with soft cuticles following their moult (2).

Mating takes place in autumn; the eggs develop whilst attached to the mother's abdomen, and the female overwinters with the eggs still attached to her. After the eggs hatch, the juveniles remain attached to the mother before becoming independent at the beginning of summer. During the first year of life, juveniles may moult more than 7 times. After they reach maturity, however, there tends to be an annual moult (2).

Perhaps the most devastating factor affecting freshwater white-clawed crayfish at present is crayfish plague, a virulent fungal disease carried by the aggressive introduced species, the American signal crayfish (Pacifastacus leniusculus)(4). Spores of this disease can be spread in the water, on wet equipment and on fish (2). Competition with introduced crayfish species has also affected our native crayfish (3); signal crayfish were first introduced to the UK in the 1970s and are now naturalised and breeding (2). Two other introduced species have become established (3); the narrow-clawed (or Turkish) crayfish (Astacus leptodactylus) and the noble crayfish (Astacus astacus) (2). Pollution and river works are also likely to have affected the species (2).

The freshwater white-clawed crayfish has been targeted as a priority for conservation under the UK Biodiversity Action Plan (UK BAP). The Species Action Plan aims to maintain the current distribution of the species through a combination of restricting the spread of non-native crayfish and crayfish plague, as well as providing suitable habitat features (3). The Environment Agency has carried out research into potential methods of controlling the signal crayfish, and is currently investigating the use of pheromones to lure this introduced species into traps (5). It is an offence under Schedule 9 of the Wildlife and Countryside Act to release the three introduced species of crayfish into the wild (3).

The UK BAP Species Action Plan is available at:
http://www.ukbap.org.uk

For more on the Environment Agency see:
http://www.environment-agency.gov.uk/

Information authenticated by the Environment Agency:
http://www.environment-agency.gov.uk