Conservationists have released almost 200 white-clawed crayfish – one of the UK’s most endangered native species – into the wild to help boost the rare crustacean’s dwindling numbers.

Experts from Hampshire & Isle of Wight Wildlife Trust and Bristol Zoological Society released the crayfish into a safe section of the River Itchen’s upper reaches in a coordinated effort to safeguard the species’ future.

The crustaceans, which are the UK’s only native freshwater crayfish species, had been reared from eggs by the Bristol Zoological Society, to ensure they had a good chance of survival when released into the wild.

Altogether, 192 crayfish were released in time for the breeding season.

Despite once being common and widespread in British rivers and stream, white-clawed crayfish numbers have declined dramatically by at least 70% across the UK since the 1970s. This decline has been even more severe in Hampshire.

They are currently threatened with extinction due to pollution, habitat loss and, most prominently, the spread of invasive crayfish species, such as North American signal crayfish, which carry crayfish plague, a disease that is deadly to our native species.

The release forms part of Hampshire & Isle of Wight Wildlife Trust’s Southern Chalkstreams Project, which aims to protect chalk stream habitats and the species that call them home, especially white-clawed crayfish.

Dr Ben Rushbrook, the Trust’s principal ecologist who leads on the white-clawed crayfish conservation project, said: “This, and earlier releases have allowed us to extend the range of white-clawed crayfish on this catchment of the River Itchen.

“This will increase the species’ long-term security, by providing it a degree of resilience to the impacts of potential threats, such as pollution.

“Working with the Bristol Zoological Society to rear and breed crayfish of Itchen provenance in captivity allows us to achieve this, without impacting the population in the species’ existing range.”

With funding from The Vitacress Conservation Trust, the Trust’s Southern Chalkstream Project has contributed to the release of over 1,400 captive-born white-clawed crayfish in the past eight years.

As well as Bristol Zoological Society, partners on the project include Natural England and the Environment Agency.

Dr Jen Nightingale, UK conservation manager at Bristol Zoological Society, said: “We have worked so hard to successfully breed this endangered species, so seeing them return to their natural habitat is always a special moment for us.

“White-clawed crayfish are an important part of the aquatic ecosystem and of the food chain, but numbers are in decline and, without projects like this, the species could disappear from south west England in the next 10 years.”

The Itchen has one of the last remaining white-clawed crayfish populations in Hampshire. Earlier this year, Wildlife Trust staff and volunteers discovered a cluster of white-clawed crayfish in a river channel at Winnall Moors Nature Reserve in Winchester. Until then, the species were thought to have died out from the site over 30 years ago.

The presence of white-clawed crayfish indicates a healthy ecosystem as the freshwater invertebrates require clean, well oxygenated and nutrient-rich waters.

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