Crayfish plague has been found on Dorset’s River Allen
following an investigation by the Environment Agency and Dorset Wildlife
Trust.
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.
“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,” said Andy Martin for the
Environment Agency.
American Signal Crayfish look similar to small lobsters,
they are red-brown in appearance with large, smooth claws. They are far
larger than the endangered native white-clawed crayfish.
They carry a fungal disease called crayfish plague, which
can kill native crayfish. They are active during the summer and
hibernate in winter, usually in burrows in riverbanks.
They out-compete our native white-clawed crayfish for food.
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.
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.
“Whilst we can’t be sure of the fate of the surviving
crayfish, the work we are doing on the River Allen with the Environment
Agency, such as providing cover for crayfish to hide in, will provide
any surviving white clawed crayfish a good habitat to thrive in.
“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,” added
Andy Martin.