Non native signal crayfish have a significantly adverse impact on native freshwater flora and fauna in running and standing waters. They can do this by consuming large quantities of plants and invertebrates, and by predating or displacing amphibians, fish and fish eggs. Signal crayfish can also modify aquatic environments, by burrowing into the banks of rivers and ponds. Extensive burrows may destabilise river banks, leading to increased rates of erosion, and the disturbed silts can lead to the shallowing of streams and the compaction of salmonid spawning grounds.
The River Barle is a Site of Special Scientific Interest in which Atlantic Salmon are one of the designated interest features. Natural England, with advice from the Environment Agency, has identified the presence of signal crayfish as a potential threat over time to the favourable condition of the SSSI. They highlighted the need for a systematic survey to provide a baseline against which to assess impacts on both the physical and biological interest of the SSSI. The Environment Agency has also wanted this baseline for some time, to be able to assess any future changes under the European Water Framework Directive.
To date, we know that signal crayfish are present in the River Barle from ad hoc records and some EA electrofishing data, but we do not know the extent or population density. The aim of the survey will be to carry out a systematic survey from Brushford up stream with the aim of working up towards the headwaters as time permits.
The survey will be carried out by a small team of trained volunteers who will be supported by staff from the Environment Agency and National Park Authority. The survey will involve visual searches, and the use of artificial refugees (which act as habitat refuges) and baited traps. The survey will begin in April and continue until late July. We are happy to send out the survey methodology if you would like to see it.
All surveyors carry identification and will, of course, avoid any disturbance to agricultural or riparian activities. The project team contacts land and riparian owners pre survey.
The survey results will be available in the autumn the team and we will be happy to send you a copy on request. The findings of the survey will add to the evidence base enabling an effective response towards this invasive species This project is funded by the Heritage Lottery Fund, the Exmoor Trust and Exmoor National Park. For further details please contact David Rolls, Tel: 01398 322164.
Project Partners, funders and in-kind contributories:
RETA (River Exe and Tributary Association)
RBFC (River Barle Fishing Club)
Exmoor National Park
The Environment Agency
The South West Rivers Trust
Exmoor Moorland Landscape Partnership Scheme
Exmoor Volunteer Partnership
Nicky Green – local crayfish ecologist and researcher