Until recently the River Allen’s native White-clawed crayfish population, one of the few remaining in Dorset, has managed to remain free from disease but dead and distressed crayfish were recently spotted in the river in July.
Samples were sent to the Centre for Environment Fisheries and Aquaculture Science for disease analysis and they have now confirmed that the crayfish are infected with crayfish plague.
Andy Martin for the Environment Agency said: “The crayfish plague is carried by non-native American Signal crayfish, which are not susceptible to it and are present in many of our Dorset Rivers. It is transferred to new waters either through the movement of the Signal crayfish or by water and/or damp equipment that has come from waters that contain signal crayfish. It is not clear yet how the disease reached the River Allen.”
American Signal crayfish carry a fungal disease called crayfish plague, which can kill native crayfish.
They also compete with our native White-Clawed Crayfish for food and shelter. They also cause damage to riverbanks by deep burrowing, impact on river fly populations and can reduce fish stocks by eating large amounts of fish eggs.
Monitoring the situation
The Environment Agency is working closely with the Dorset Wildlife Trust and local landowners to monitor the situation and determine the extent of the outbreak.
Dorset Wildlife Trust Conservation Officer, Amanda Broom, said: “It is very sad that White Clawed Crayfish have been infected with the crayfish plague on the River Allen, as this was one of just three populations remaining in Dorset. However, by remaining vigilant and observing biosecurity procedures such as cleaning and drying equipment and shoes that have been near the river, hopefully we can limit the amount of crayfish being affected by this disease.”
Please follow the ‘Check – Clean – Dry’ procedure
The South West Crayfish Partnership are urging river users to follow the ‘check – clean – dry’ procedure to try and contain the disease and prevent it spreading to other watercourses.
Andy Martin, for the Agency, said: “We are urging river users to ensure that any equipment they use in the River Allen is clean and dry before entering the river, when moving between locations and at the end of the day. This will hopefully limit the rate of spread of the disease through the river and reduce the risk of it being spread to other rivers that still have white-clawed crayfish populations.”
Ark sites for crayfish
Last year the South West Crayfish Project – a partnership between Buglife, the Environment Agency, Avon Wildlife Trust and Bristol Zoo – worked with Dorset Wildlife Trust to establish an Ark site for the White-clawed crayfish in the River Allen. Nearly 400 crayfish were moved to a nearby safe haven site. This site will be monitored this year to see if the population has established successfully.
Andrew Whitehouse, South West Manager for Buglife said: “I think this shows how important it is to have Ark sites for White-clawed crayfish, both as a reactive conservation tool to urgent threats and as an insurance policy – as even our strongest wild populations can be compromised.”
“We are monitoring the River Allen Ark site this summer and hope to have some good news there.”