Britain’s native crayfish could be wiped out of one of its last strongholds, the River Eden and its tributaries in Cumbria, unless all river users remain vigilant. According to Eden Rivers Trust, a Cumbrian conservation charity, the biggest threat to the native crayfish is the American signal crayfish and the crayfish plague disease which it carries. This American invader is already in the rivers surrounding Cumbria.
So far the River Eden and its catchment has managed to avoid being infiltrated by the American crayfish or its disease, which is deadly to the native variety. But conservationists are stressing how important it is to make sure that the signal crayfish is not introduced to the river, either deliberately or accidentally.
The American signal crayfish was originally brought into this country to be farmed for food but has since escaped and been deliberately released in to many rivers across the country, including the north of England. It has already eradicated the native crayfish in many river systems in England and there are fears that it could now be transferred to the Eden.
Results of a major study of the native white clawed crayfish in the River Eden and its tributaries, undertaken by Eden Rivers Trust, show that they are currently doing well in many areas, but there is no room for complacency.
“It would be a disaster if the American signal crayfish arrived in the Eden valley. The two kinds of crayfish can’t exist side by side and it would undermine all the hard work carried out by conservationists, land owners and river users over many years,” says Maggie Robinson, Manager of Eden Rivers Trust, a charity set up over 10 years ago to conserve the river.
Where the two types of crayfish have mixed, the native crayfish has been wiped out. The signal crayfish is not only larger and more aggressive than its native counterpart, it damages river banks by burrowing, eats fish eggs and young, and carries the disease, crayfish plague, which kills the native variety.
As well as being deliberately introduced in to rivers, there are a number of accidental ways signal crayfish and their disease can arrive. One is when fish stocks are released into a river for angling purposes – either young signal crayfish or crayfish plague can be unwittingly transferred to the new river. Another is the possibility of river users like fishermen or canoeists inadvertently transferring crayfish plague into another river, if equipment is not washed, dried or disinfected properly.
Eden Rivers Trust advises that anyone moving from other rivers to the Eden should:
Wash all mud, weed, etc off all equipment thoroughly;
Dry all equipment completely;
If complete drying is not possible, disinfect equipment with an iodine-based disinfectant.
For more information on the native white clawed crayfish, the American signal crayfish and how to prevent its spread, go to edenriverstrust.org.uk.
