River Barle Signal Crayfish Project

Signal crayfish underwater

In 2014 a population of the signal crayfish (Pacifastacus leniusculus) was found along a five mile stretch of the River Barle, designated a Site of Special Scientific Interest (SSSI) for its unmodified natural ecosystem.

Signal crayfish are one of the most widespread and damaging non-native invasive species in the UK. They are responsible for severe declines in populations of the native white-clawed crayfish (Austropotamobius pallipes) as well as having notable effects on wider floral and faunal communities. Negative impacts include:

- Carrier of the crayfish plague (Aphanomyces astaci) which our native crayfish are very susceptible to.

- Predation

- Competition for food and shelter from predators

- Increased siltation and flooding due to a high degree of burrowing in riverbanks leading to erosion.

The Trial

The River Barle Signal Crayfish Project, led by Nicky Green Associates, is an innovative volunteer focused approach attempting to control signal crayfish within our trial area on the River Barle. The project started in 2015 and the combination of trapping and male sterilisation has not been trialled in the UK before.

River Barle Crayfish Project volunteers

Our dedicated team of volunteers are out on the River Barle between April and October. Artificial refuge traps are checked weekly, the larger males are sterilised and returned and all other signal crayfish are humanely dispatched on site. Important information relating to the population structure is collected to help us determine if this method is working and so far, the results are looking promising.

You can find out more about the River Barle Signal Crayfish Project from the video below, an episode from ‘Nature Natters’ North Devon Biosphere’s ‘Pledge for Nature Project. Pledge for Nature hopes to inspire you to take action for nature.

We need your help!

Alongside the River Barle Signal Crayfish Project we have volunteers surveying for signal crayfish on some of Exmoor's other rivers and have since discovered them on the Exe as a result. If you have seen any invasive species within the National Park or would like to volunteer please visit our Get Involved page.

We can also give advice, so if you have an invasive species on your land that you are looking to control please do not hesitate to get in touch by email or phone.