THE northern stronghold of native crayfish, in the rivers Wansbeck and Aln, could be under threat from the spread of the aggressive signal crayfish, Environment Agency officers have warned.

Angling clubs, conservation groups and other organisations have all been warned that North American signal crayfish have been discovered in the River Derwent near Blaydon. As a result special measures have been put in place to try to halt their spread.

The first report came last month when Agency officers were informed by staff at Gateshead’s Thornley Woods Centre that they had found two signal crayfish – one alive and one dead.

Further surveys revealed another female signal crayfish at Thornley Woods. This was removed by Agency staff.

Agency conservation officer, Anne Lewis, said: “At the moment, the signal crayfish seem to be present in the Derwent in low numbers but it is essential that we take every step to prevent their spread.

“The American species of crayfish is bigger, more aggressive and out-competes our native crayfish. Most importantly it also carries a fungal disease known as crayfish plague that has wiped out our native crayfish from most rivers in the south of England.”

The bid to stop the spread of the signal crayfish into rivers which are home to the smaller, native white-clawed crayfish, includes:

Disinfection procedures. This can be as simple as ensuring angling equipment is thoroughly dry when moving between rivers

A halt to the transfer of fish from the Derwent to catchments which are home to native crayfish

Informing everyone about the problem and how to prevent the spread to important crayfish rivers.

If anyone discovers signal crayfish in the area please let the Agency know by contacting the free emergency number on 0800 80 70 60. Please note that it is illegal to keep or release to the wild any crayfish without a special licence from Defra, if they are non-native, or English Nature, if they are native.

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