Our crayfish expert Alex Prendergast took part in a translocation project yesterday, moving native white-clawed crayfish from a North Norfolk river to a safe receptor, or ark, site. Crayfish enthusiasts from across the region and beyond met at a section of river known to hold one of East Anglia’s best remaining natural populations of white-clawed crayfish. Unfortunately, as has been the case in most of England’s rivers, this population is now doomed due to the arrival of signal crayfish in the watercourse further upstream.To find out more about crayfish read the Norfolk Biodiversity Partnership Species Action plan
Suitably disinfected, we spent the morning in the river catching white-clawed crayfish. The target was 150 large healthy animals. Where there are no major stones or other refugia in the channel the largest crayfish are usually found in burrows in the bank. This gave us the opportunity to practise a technique known as ‘crayfish tickling’ which involves fumbling about the bank underwater until a burrow is located and sticking a hand in to see who’s at home. Crayfish were carefully extracted from the burrows, sometimes requiring a few strategic pokes to encourage them to vacate. Once caught the crayfish were screened for porcelain disease, measured and sexed. Only large, healthy animals and a roughly equal ratio of males to females were selected to start the new population at the ark site. A red kite cruised by, briefly distracting attention from our cold-numbed hands.
After lunch and a final push to meet our target ten people, lots of wet equipment and 150 crayfish squeezed into a few cars for the trip to the receptor site – a chain of three recently restored spring-fed ponds on a North Norfolk estate. Tests carried out the week before showed the water to have ideal chemistry for crayfish and the ponds with their crystal clear water and abundant plant and invertebrate life look like an ideal new home. As we released the crayfish, it was great to see them burrowing through the aquatic plants and investigating niches amongst tree roots. We are confident that the new population will succeed in this ark site and future monitoring is planned to check that they do.