After more than a year of specialist care, 348 endangered white-clawed crayfish (Austropotamobius pallipes) have been released into protected waters in Northumberland.
The juveniles were reared at Northumberland Zoo after hatching from eggs carried by females rescued from the River Wansbeck in late 2024. Their release into carefully selected “ark sites” marks the completion of the first stage of a conservation project aimed at protecting one of Britain’s most threatened native freshwater species.
The project began in November 2024, when Northumberland Zoo joined the Environment Agency, Tyne Rivers Trust and the National Trust to rescue female white-clawed crayfish carrying eggs — known as “berried” females — from the River Wansbeck.
The operation followed the discovery of unexplained deaths and unusual symptoms in one of the world’s highest-density populations of the species. The females were transferred to the zoo, where their eggs hatched safely in spring 2025. The adults were then returned to the river, while the young remained at Northumberland Zoo to be reared until they were large enough for release.
Over the following year, the zoo’s team monitored and cared for the juvenile crayfish until they reached the minimum body length of 20 millimetres required for release.
On the recommendation of the Environment Agency, the 348 animals were then transferred to protected “ark sites”: isolated water bodies selected to allow white-clawed crayfish to establish and reproduce away from some of the threats affecting populations in the wild. Their precise locations are being kept confidential to protect the species.
“As our facility was built for a much smaller number of berried females, it was quite a jump going from the 3 females we had in early 2024 to the 53 that were taken in during this rescue,” said Lucy Edwards, Curator. “I’m really proud of the amount of effort that the keeper team put into learning about the husbandry of this species, as well as the intense problem-solving required for such a sensitive species. We faced the challenge head-on and it all paid off seeing the 348 craylings released in Northumberland.”
More than 1,500 hours of specialist care
Despite their small size, the crayfish required intensive care. According to Northumberland Zoo, the project involves more than 1,500 hours of staff work each year, including daily husbandry, water-quality monitoring, record keeping, licensing, meetings and conservation planning.
White-clawed crayfish require very specific water conditions and are considered an important indicator of freshwater ecosystem health. They are also a keystone species and form part of the diet of native European otters.
“White-clawed crayfish might not be the animals that people first come to a zoo to see, and they can be a challenging species to get people to love when they don’t have big eyes and fur. But our commitment to them is a huge testament to our devotion to protecting native species,” said Zoo Manager Maxine Bradley. “They may be tiny, but caring for them is incredibly complex, with very specific water parameters needed for them to thrive, and every detail matters. They are a keystone species and an important indicator of a healthy water system, as well as an important food source for our native European otters, so the impact of protecting them goes far beyond the animals themselves. We hope that by sharing their journey with our visitors, we can help more people discover and value this remarkable native species. Conservation isn’t measured by the size of the species, but by the impact we can have on its future.”
Britain’s only native freshwater crayfish
The white-clawed crayfish is classified as Endangered and is Britain’s only native freshwater crayfish. Populations are threatened by habitat loss, invasive American signal crayfish and crayfish plague.
The River Wansbeck remains particularly important for the species, supporting one of the highest-density populations of white-clawed crayfish in the world.
The release of the 348 juveniles is only the first stage of the project. Northumberland Zoo is now planning a purpose-built conservation facility specifically designed for the long-term breeding, care and recovery of white-clawed crayfish, building on the husbandry experience developed during the initial programme.
