White-clawed Crayfish Surveys
White-clawed crayfish. Also known as Atlantic stream crayfish, are Britain’s only native freshwater crayfish. They look like miniature lobsters, measuring just 10-12cm long and are an olive/brown colour. White-clawed crayfish are found in freshwater streams, rivers, canals and lakes where they find submerged crevices among stones, tree roots or burrow into earth banks. Our native crayfish are under serious threat from exotic signal crayfish species that displace our white-clawed crayfish, and from a fungal pathogen to which the signal crayfish are immune, but is virtually 100% lethal to our native species. White-clawed crayfish are also under threat from industrial, agricultural and domestic pollution, land drainage and riparian engineering works to deepen and straighten watercourses.
Since the 1970s, approximately 70% of the UK population of white-clawed crayfish has been lost. It is listed on the Government’s Section 41 Priority Species List and under the Wildlife and Countryside Act it is illegal to take or sell white-clawed crayfish.
Surveys for white-clawed crayfish should be carried out if historical presence or local conditions suggest that they might be present. A licence may be issued by Natural England for operations in relation to maintenance or engineering works which affect the species. A licensed ecologist should carry out the surveys where methods often include; manual searches, hand netting, trapping and night viewing. The recommended optimal period for carrying out surveys is July to September. Late May and June should be avoided as the females may be carrying newly hatched young. Following identification of white-clawed crayfish, the impacts of the development on the habitat should be assessed. Re-designing the scheme to avoid negative effects is the priority, however, if this is not possible, mitigation measures should be used to assess the impacts. These can include; reducing disturbance to the river bank, reducing water pollution including silt, reducing the area affected and working in discrete sections, adding appropriate vegetation and excluding crayfish. Compensation measures will be required if there is still a negative impact. These can include creating new habitats and moving the crayfish within the catchment area.
Please call us to discuss your project so we can advise on the most appropriate survey protocol and best course of action.