Saltaire Village, World Heritage Site
Image by Dan Bailey




Saltaire Village World Heritage Site
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Added to website: 30 January 2013
Signal crayfish in the River Aire

Peter Bottomley writes: All over Great Britain, living in most of our rivers is the alien signal crayfish; this crustacean can grow up to 100cm and live for up to 20 years. It has been found in traps at Silsden and it is on its way down stream to Saltaire, so the fish pass in the proposed water turbine will allow the problem more easily to flow further down the river. The plague it carries is rapidly fatal to the British crayfish (about 3 weeks), a white oval patch on its claw hinge gives it the name 'signal' because it resembles the train signalman's flag and it is bluish brown in overall colour.

The crayfish was first brought to Europe in the 1960s as an extra food stuff but escaped from farms into the rivers. The deadly North American Pacifastacus leniusculus species was introduced into Great Britain in 1976 and in 1981 it was discovered in our fresh water rivers. The signal crayfish lays about 300 eggs in the autumn and they mature in about 3 years. Crayfish have been around for 30 million years. They are very robust and live well in our waters by eating young fish and most decaying materials. They bore into the river banks to nest and by the look of it are around to stay but they are in turn eaten by birds, rats and otters. Some people keep them as pets in tanks but they can climb the walls and escape. They are farmed in many places around Great Britain but should be licensed in certain areas by MAFF.

The young fish and the virus spores they carry can be washed down river with the flow; also the spores can be carried on damp tackle by river fishermen from one river to another, so the problem seems just unstoppable. The Environment Agency is said to be having some success in planting pheromone traps and anglers are asked to kill any signal crayfish that they catch, but the invaders are very hard to stop. The problem is also occuring in Japan and Australia.


Peter Bottomley



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