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The Freshwater Crayfish in Derbyshire and the Peak District.
The introduction of the non native signal crayfish is posing significant problems for the native White Clawed Crayfish in Derbyshire and also the rivers of the Peak District.
The white clawed crayfish is a dull olive-brown colour with a lighter underside to their claws, hence their name. They need unpoluted water with low sediment levels and generally grow to less than 10cm in length. They mate in October/November and the females lay eggs which are attached in clusters to her abdomen. The following spring, they hatch and the young remain attached to the mother until they are self sufficient, usually mid summer. They thrive in habitats where there are plenty of niches in which they can hide from their predators - that is why the rivers of the Peak District are perfect.
A variety of non-native species have been either released or escaped and the signal crayfish has become particularly well established in Derbyshire. The signal crayfish was introduced in order to try to develop stocks of crayfish that were immune to 'crayfish plague'. The problem was that the imported crayfish were carriers of the disease, even though they did not develop it. The result was the decimation of the native crayfish numbers. It is triggered by a type of fungus, the spores of which are easily transported by anglers and anyone who has been near a source of the fungus in wet weather. But it is not just the fact that they carry the plague fungus, they prey on the smaller native species and their burrows in the river banks are so extensive that they cause a lot of damage.
There have been two big outbreaks of crayfish plague this century, in 2005, the river Dove was hit, with hundreds of white clawed crayfish being found dead on the banks and in 2008 the river Manifold crayfish suffered a similar fate.
In order to try to save the native species from extinction, native crayfish have been captured and transferred to placed that are unlikely to be colonised by the non-native types. This has been done by licenced operatives from the National Trust and Natural England since trapping crayfish is illegal as they are a protected species. However there are still people around who are selfish and irresponsible (or just too stupid to be able to understand) enough to trap any crayfish, native or otherwise, in Derbyshire. These idiots also endanger two other fully protected species - the otter and vole because they can become stuck in the crayfish traps and drown. It is also illegal to release non-native crayfish into the wild, that includes allowing them to escape from captivity.