Wild Life - Winter 2022

Crayfish surveys offer hope for endangered species

A cluster of endangered crayfish discovered at one of our nature reserves earlier this year are more widespread than we originally thought, according to the results of our ecological surveys.

The group of white-clawed crayfish – the UK’s only native crayfish species –were found by a team of Trust reserves officers and volunteers within a sanctuary area at Winnall Moors Nature Reserve in January.

Until then, it was thought the crustaceans had died out from the site in Winchester over 30 years ago after a deadly plague wiped out local populations.

Following the remarkable discovery, this summer we carried out four surveys to monitor the crayfish and attempt to determine their relative strength and distribution at the reserve.

To survey them, our expert ecologists check a series of artificial refuge traps

that had been deployed in the water to recreate the cosy shelters the crustaceans seek out.

The crayfish hide inside the submerged traps – essentially a row of connected plastic tubes of varying diameter –which makes it easy to check them for inhabitants.

Once a crayfish has been found, the ecologists record its sex, size, and any signs of damage or disease before returning it to the water – this crucial data helps estimate the strength of the population.

Between 17 and 20 crayfish were found during each survey. This included juveniles, which is a promising sign the group is established at the reserve, as well as an individual recorded in a distinct water channel from the original discovery.

Conservationists have worked for decades to recover the UK’s white-clawed crayfish populations. Nationally, their numbers have declined by at least 70%

since the 1970s due to pollution, habitat loss and the introduction of non-native crayfish and a disease called crayfish plague that’s carried by species from North America.

Over 10 years ago, the Trust embarked on an ambitious floodplain restoration programme, reconnecting relict water meadow carriers and improving river and stream habitat. This will have increased the amount of preferable habitat for white-clawed crayfish and hopefully contributed to their survival at Winnall Moors Nature Reserve.

Find out more about the Wildlife Trusts’ efforts to support the long-term survival of white-clawed crayfish at hiwwt.org. uk/southern-chalkstreams