The white-clawed crayfish, the UK’s only native crayfish and freshwater relative of the lobster, is to be given a much needed helping hand in the South West. A project between the Environment Agency, Avon Wildlife Trust and Bristol Water heralds the start of a concerted effort in the next few years to curb the dramatic decline of native crayfish across the region, by translocating them from threatened areas to specially selected refuge streams.
The first rescues will take place this week when a population near Bristol is transported in cooled tanks to its new habitat. White-clawed crayfish are threatened throughout their European range from changes to habitat, water quality and pollution. However, the increasing threat is from non-indigenous crayfish species (NICS) such as the American signal crayfish.
‘Signal crayfish aggressively push out native crayfish and most devastatingly, carry a fatal fungal disease responsible for wiping out many British populations’ said the project’s coordinator Lydia Robbins of Avon Wildlife Trust, ‘due to crayfish ‘plague’ the Bristol Avon catchment has recently lost three of its four most abundant native populations. Unfortunately research into fully eradicating signal crayfish from river systems, including by intensive trapping has to date proved unsuccessful. ‘
The alien invaders were originally imported for food in the 1970s, but have escaped or been illegally released into the wild. They also threaten more than our crayfish as new research shows their extensive impact on other species, such as trout and salmon numbers.
‘Translocating white-clawed crayfish to refuge sites mitigates the threat from American signal crayfish by actively conserving populations' said Peter Sibley from the Environment Agency, ‘it is hoped by introductions to more isolated areas they will re-establish because they are an important part of river ecosystems in the South West’.
As Britain's largest freshwater invertebrate they are a natural component of other animals' diet including trout, otters and herons. To avoid predation crayfish are nocturnal, hiding in refuges during the day. As omnivores their diet of plant and animal matter varies widely, from fallen leaves to small invertebrates and fish.
‘It was important not to harm the resident ecology when transferring crayfish to new sites so scientific tests examining water quality and in-stream and riparian cover have been undertaken’ said Peter Sibley.
‘It is also imperative we carefully monitor these translocations to evaluate their success so as to inform further strategic conservation’ added Lydia Robbins, ‘and to clarify that trapping American signal crayfish for food is not of any conservation benefit, contrary to popular belief, and increases the risk of spreading crayfish plague.’
Peter Sibley went on to say ‘the public can help our efforts in avoiding the spread of plague by drying out/disinfecting angling equipment between sites. We stress white-clawed crayfish are protected by law and a licence is required to catch any kind of crayfish in Britain.’
Jeremy Williams of Bristol Water commented ‘we are very pleased to be involved in such a project, the security of the species may well depend on such efforts.’
If you have spotted a crayfish or for related advice, contact your local Environment Agency office.