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The white clawed crayfish Why does the white clawed crayfish need help? The white clawed crayfish (also known as the Atlantic stream crayfish) is the only freshwater crayfish native to the British Isles. The species is widely distributed nationally, although naturally absent from western Wales, Scotland, and parts of western England and Ireland. It was once widespread across much of Europe but has suffered a serious decline across its range and is considered to be a globally threatened species. How do I recognise a white clawed crayfish? • Crayfish look rather like small lobsters growing to about 10 or 12 cm in length. • The body is smooth, pitted and brown to olive in Natural England colour. • They have large fearsome-looking claws have pale undersides (hence the common name) but are darker and rough above. These are larger in the male. White clawed crayfish • They walk using their four pairs of legs and can propel themselves quickly through the water with vigorous flicks of their fan-like tails. Where do you find white clawed crayfish? In Britain the white clawed crayfish requires clear, welloxygenated waters that contain enough calcium to form their outer (exo) skeletons. This means they are usually found in fast flowing streams, brooks, and rivers, but can also be found in reservoirs and quarry pools that are relatively free of fine sediment. Crayfish are active mainly at night, hiding by day under stones, tree roots, submerged plants or in burrows and crevices in the riverbank. What do they eat? Native crayfish are omnivorous, feeding on both plant and animal matter. They prey on snails, insect larvae and scavenge for dead fish and vegetable matter. Like other species of crayfish they are sometimes cannibalistic – occasionally feeding on the softer-bodied young of their own species. Suffolk Wildlife Trust What are its predators? Juveniles are particularly prone to predation by fish, such as trout and perch, dragonfly and aquatic beetle larvae, and mature crayfish. Adults fall prey to rats, mink and herons, especially after moulting when their bodies are soft. In some parts of the country they are an important source of food for otters. Lifecycle Crayfish take 3—4 years to reach reproductive maturity and mate in October or November. Around 100 fertilised eggs become attached to the underside of the female’s abdomen and spend the winter in this state. The eggs hatch into tail-less, miniature crayfish in the late spring where they continue to cling to their mother before moulting into a second stage with a rounded hairy tail fan about three weeks later. The juveniles then leave their mother and undergo up to five more moults before reaching adulthood after their first year. In subsequent years, the adult crayfish undergo an annual moult. After Brooke House, Ashbocking, Ipswich IP6 9JY Tel: 01473 890089 Fax: 01473 890165 Email us at [email protected] or visit our website at www.suffolkwildlifetrust.org Registered Charity No 262777 Creating a Living Landscape for Suffolk moulting, crayfish are soft and particularly vulnerable to predation. Crayfish may have a life span of between 7 and 12 years taking up to six years before they reach full size. Threats to white clawed crayfish • Poor water quality White clawed crayfish are susceptible to pollutants such as fertiliser run-off and sewage which lowers the oxygen concentration in water. They are also vulnerable to certain pesticides especially synthetic pyrethroid insecticides. • Site and catchment management Stream bed management can destroy or damage their habitat and watercourses may become unsuitable for crayfish through erosion of soil within the catchment, which reduces water quality and clogs streams. • Crayfish plague This disease is caused by the fungus Aphanomyces astaci and is a serious contributory factor to the national decline of the white-clawed crayfish. Many populations of the native species, especially in the south, were lost to the disease from the 1980’s onwards. It is thought that the disease is mainly spread by the non-native species which appear to be unaffected. Spores of the fungus can spread through water and can become attached to fish scales, mud and angling equipment. The fungus causes abnormal behaviour (eg walking about during the day) and blotching of the exoskeleton before death. There is no means of eradicating crayfish plague. • Competition for food and habitat from introduced crayfish species Four introduced crayfish species have become established in the wild in the UK, two of which, the Turkish crayfish and the North American signal crayfish, have become widespread and abundant in British waters. Both of these species, which arrived in the 1970’s, can out-compete the native species for resources and may even prey upon it. Legal protection White clawed crayfish are protected under Schedule 5 of the Wildlife and Countryside Act (1981) and cannot be killed, kept, sold or handled without a licence. The same Act also prohibits the release of exotic crayfish into the wild. How can I help native crayfish? • Equipment used in waters where non-native species are present, or where native crayfish mortality has occurred, should be thoroughly dried before use and treated with a proprietary disinfectant before further use. • Report sightings of native or non-native crayfish to the project (see the address below). Other relevant SWT factsheets: • Creating an ‘otter haven’ • The water vole • The European otter • Relevant conservation grants For further advice, contact Suffolk Wildlife Trust on: 01473 890089 [email protected]