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American signal crayfish which have been introduced
to Britain represent a major threat to the natural
ecology of our rivers. These animals have spread
rapidly in many rivers, especially in England.
Their numbers are prolific and they can dominate
those environments they invade. They eat almost
anything, vegetable matter, carrion or fish if
they can get them. They threaten fish because
they can hide in crevices below stones or under
banks, which fish like young salmon and trout
also use during the winter or during spates.
By 2006 signal crayfish were present in the upper
Earn and several other locations in Tayside but were not known to be present in
the Tay, but they were present in a pond from which
they could potentially escape into a tributary
of the Tay.
As that population of crayfish represented a direct threat which might still be prevented, the Tay Foundation contributed to a project
to eradicate it before the crayfish spread
to the river, from which it would be impossible
to remove them. The procedure used to eradicate
them was novel and had only once been used previously
in Britain, in some ponds near Edzell in 2004.
The project was very challening but considered successful. However, since that time another population of signal crayfish has been found and in the autumn of 2010 it was confirmed that crayfish from this other population have in fact become established in a tributary of the Tay from which eradication may now be impossible.
A report on the 2006 eradication project is provided below.
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