English crayfish claws back from the edge

Humanity is helping the native English crayfish make its last stand on one of the country's finest chalk streams - having caused the crustacean to be almost wiped out in the first place.

Five years ago the crayfish, which resembles an elegant miniature lobster, was widespread along the length of the Hampshire Itchen, a near pristine river which flows through Winchester. Now it survives in only one location in the headwaters of a tributary, the Cheriton stream. The disaster has been caused by a lethal fungal disease, introduced with the American signal crayfish.

It's the same story for streams and rivers across southern England, from Cornwall to Kent. The American arriviste, which is immune to the disease, is marching northwards.

If the fungal plague does not kill the native species, then the new arrival appears to do the job itself. Being bigger, more aggressive and mobile it can out-compete the Englishman and is also known to eat it.

The American was brought here in the 1970s to be reared in tanks and ponds for human consumption. It soon escaped into the wild along with three other non-native crayfish species which pose a lesser threat to the local variety.

There are thought to be only about 2,000 native, or white clawed, crayfish in the surviving colony in the stream at Alresford, near Winchester. Thirty have been captured, including females carrying fertilised eggs, and are being raised at nearby Sparsholt College.

The hope is that they will breed and provide a captive population which can be released back into the Itchen some time in future if the colony is wiped out. The native crayfish is protected by law, while releasing the invaders into the wild is now a crime.

The government's Environment Agency is also hoping to boost the colony's numbers by improving the underwater habitat for the crayfish. Ten tonnes of large, knobbly flintstones are being placed along a 100 yard-stretch of stream bed. These provide the nooks and crannies the crayfish need to shelter in.

Tim Sykes, the agency's conservation officer in Hampshire, said: ``The crayfish plague worked its way upstream at an amazing speed. Two summers ago there were just two colonies left and now we're down to one.''

He found a female nestling in a hole in a stone. Folded into her curled up tail was a cluster of ball-bearing sized eggs, which she protects all through the winter and spring. She emerged after a moment, signalling her displeasure by giving him a sharp nip on the hand. The agency is working with local conservation groups in Yorkshire, surveying streams and rivers for the native and the aliens.