HUNDREDS of endangered crayfish have been released at a secret site in the River Itchen.

In a bid to boost the crustacean numbers in the UK, conservationists have released 200 white-clawed crayfish into the Hampshire river.

They are one of the UK's most endangered native species and the release is hoped to secure the species' future. They were released in time for breeding season and have been reared from eggs.

The release was organised by experts from Hampshire & Isle of Wight Wildlife Trust and Bristol Zoological Society.

Despite once being common and widespread in British rivers and stream, white-clawed crayfish numbers have declined dramatically by at least 70 per cent across the UK since the 1970s.

Hampshire Chronicle: Almost 200 endangered white-clawed crayfish were released into a safe section of the River Itchen in Hampshire Almost 200 endangered white-clawed crayfish were released into a safe section of the River Itchen in Hampshire (Image: Hampshire & Isle of Wight Wildlife Trust)

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.

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.”

Hampshire Chronicle: Conservationists from Hampshire & Isle of Wight Wildlife Trust and Bristol Zoological Society collaborated on the releaseConservationists from Hampshire & Isle of Wight Wildlife Trust and Bristol Zoological Society collaborated on the release (Image: Hampshire & Isle of Wight Wildlife Trust)

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

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.”