1,000 crayfish released into river at Builth Wells Published duration 8 May 2014

image copyright Natural Resources Wales image caption Native crayfish numbers have been affected by non-native American signal crayfish and pollution

More than 1,000 native white-clawed crayfish have been released into a river in Powys in a bid to "save the species from extinction".

Natural Resources Wales (NRW) has reared and released over 2,700 captive reared crayfish into the wild in the last three years.

The latest juvenile batch were released in a river tributary near Builth Wells.

Native crayfish numbers have been affected by non-native American signal crayfish and pollution, say officials.

They have been released into specially selected "ark" sites on a tributary of the River Irfon after being reared at NRW's Fish Culture Unit with help from local ecology charity the Wye and Usk Foundation.

image copyright Natural resources wales image caption The project is part of wider work to mitigate threats facing the crayfish

The release sites are chosen for their habitat and water quality and because they are free from non-native crayfish and crayfish plague, a disease carried by the American crayfish.

White-clawed crayfish have been found at release sites 15 months after the initial introduction which experts say is a good sign given the white-claw is Britain's only native crayfish and at "real risk" of becoming extinct from mainland Britain.

Their sensitivity to chemical pollution is also a useful indicator of water quality so establishing a healthy population "would be a good sign that we are creating a better environment in Wales", according to Oliver Brown from NRW.

"Rearing in excess of 1,000 crayfish in one production cycle is a real breakthrough for us," he added.

"With few naturally abundant populations left in Wales, captive rearing is likely to be the most efficient way of providing crayfish to stock ark sites.