Saving Devon's Native Crayfish - Connecting the Culm

The River Culm is home to the white-clawed crayfish, the UK’s only indigenous freshwater crayfish. Sadly, the white-clawed crayfish has seen a decline of over 70% in the South West in the last 50 years and is now recognized as globally endangered (IUCN) and is protected under the Wildlife and Countryside Act 1981.

The sharp decline in the species has been driven by habitat degradation, pollution, deteriorating river water quality, but primarily the introduction of the invasive, non-native American signal crayfish and its associated pathogens. Signal crayfish not only carry a deadly crayfish virus which kills white-clawed crayfish, but they also prey and outcompete the native crayfish for food.

White-clawed crayfish are a smaller, less aggressive species which produce fewer young. Signal crayfish produce greater numbers of young and mature faster. Unlike our native crayfish species, signal crayfish burrow extensively into riverbanks and predate coarse fish and eggs, which means that there is also a risk of soil erosion, flooding and deterioration of ecosystem health if they are present.

White-clawed crayfish being checked at Wildwood Devon hatchery

Devon has only two remaining fragile wild populations of white-clawed crayfish, both of which are under threat of extinction from expansion of American signal crayfish and declining water quality. Learn more about the two remaining populations in the table below.

River	White-clawed crayfish population
Culm	White-clawed crayfish were believed to have died out on this river in the 1980’s but were rediscovered in 2006. Surveys during the summers of 2018 and 2019 established that a population of white-clawed crayfish survives along a km stretch of river between Hemyock and Uffculme. Surveys also established that signal crayfish populations are present above and below the native crayfish in the main river and its tributaries. The white-clawed crayfish is slowly disappearing at the upstream edge of its range in response to the downstream expansion of signal crayfish.
Creedy Yeo	Surveys during the summers of 2021 and 2022 established that a population of white-clawed crayfish survives along a 5km stretch of river between Crediton and Newton St Cyres. Native crayfish were previously found over a much wider length of the river but now only around 10% of the original population survives. Since 2005 signal crayfish have expanded downstream and white-clawed crayfish have disappeared from areas where they are present.

River

White-clawed crayfish population

Culm

White-clawed crayfish were believed to have died out on this river in the 1980’s but were rediscovered in 2006.
Surveys during the summers of 2018 and 2019 established that a population of white-clawed crayfish survives along a km stretch of river between Hemyock and Uffculme.
Surveys also established that signal crayfish populations are present above and below the native crayfish in the main river and its tributaries.
The white-clawed crayfish is slowly disappearing at the upstream edge of its range in response to the downstream expansion of signal crayfish.

Creedy Yeo

Surveys during the summers of 2021 and 2022 established that a population of white-clawed crayfish survives along a 5km stretch of river between Crediton and Newton St Cyres.
Native crayfish were previously found over a much wider length of the river but now only around 10% of the original population survives.
Since 2005 signal crayfish have expanded downstream and white-clawed crayfish have disappeared from areas where they are present.

Without intervention it’s likely that this keystone species may become extinct in Devon rivers within the next decade.

Two people in the river undertaking a crayfish survey

How can our native crayfish be saved?

Unfortunately, at present there is no way of eradicating American signal crayfish or effectively reducing their numbers in our rivers (without causing unacceptable environmental damage to other aquatic species).

Conservation methods are therefore currently focused on ensuring white-clawed crayfish populations do not become extinct by establishing a Devon crayfish hatchery and subsequent breeding populations in ‘ark sites’ (usually still waters or tributaries away from the threat from American signal crayfish) ahead of potential future river re-introductions.

Addressing deteriorating water quality in our rivers is an equally important aspect but there are no quick wins due to the scale and complexity of the issues involved.

What is happening in Devon to safeguard our native crayfish?

The good news is that a range of organisations including the Blackdown Hills National Landscape, Wild Planet Trust, Wildwood Trust and South West Water have been working over the last number of years to ensure white-clawed crayfish do not become extinct in Devon.

Led by the Wildwood Trust, the Saving Devon’s Native Crayfish project is the latest project to step up conservation efforts. Thanks for funding from Natural Englands Species Recovery Programme, the project is developing a new crayfish hatchery and wildwood Devon, will be building a bespoke ark site and creating a new crayfish education display at Wildwood Devon.

During September crayfish specialists and Widlwood Devon staff have been completing native crayfish surveys on the Culm and Creedy and have successful translocated animals from the river to the hatchery to establish captive breeding populations (fingers crossed they mate this autumn!). Once the mating season is over, most of the males will be returned to the rivers and the females will hopefully carry the fertilised eggs over winter, before the young crayfish hatch in early summer. These captive bred/raised crayfish will then be cared for at the hatchery until they are big enough to be released into ark sites or river tributaries where they are safe from the threat of invasive signal crayfish.

Crayfish specialist Dr Jen Nightingale (left) and Wildwood Devon Conservation Manager Charly Mead (right) undertaking a crayfish survey

More surveys will be undertaken in the Culm in 2024 and 2025 and the survey team would welcome help from any interested volunteers. For more information contact hello@connectingtheculm.com