- Norfolk Rivers Trust used eDNA to track the UK endemic white-clawed crayfish (WCC), and the invasive signal crayfish in UK rivers.
- The project detected WCC in a previously undiscovered WWC habitat which can now be protected and detected the invasive signal crayfish in a site that was thought to be safe.
- This project gave a valuable insight into crayfish distributions with directly applicable management outcomes.
Native white-clawed crayfish used to be present in most Norfolk rivers but have been decimated by invasive signal crayfish and are now extinct in most of their range, and the three remaining populations are threatened by the proximity of signal crayfish. As part of their work to protect and restore internationally rare chalk-fed rivers, Norfolk Rivers Trust (NRT) aimed to:
- Use eDNA to track both native and invasive crayfish in UK rivers.
- Gain insight into crayfish distributions in order to inform management decisions.
This involved detecting remnant populations of WCC so that they could be protected, while also ensuring that potential WCC reintroduction sites were free from the invasive signal crayfish.
We used the NatureMetrics aquatic eDNA service to survey for native white-clawed and invasive signal crayfish, and the experience was very good, including the guidance provided by technical staff and the practicalities of shipping and processing equipment and samples, which all worked well. NatureMetrics were also good at helping with interpretation of the results – The technical backup was excellent with great advice on sampling and interpretation of eDNA results.
Dr Jonah Tosney, Technical Director, Norfolk Rivers Trust
Species Are Difficult to Survey
Remnant populations of the native white-clawed crayfish are incredibly difficult to find by conventional trapping methods. In the past, it would take at least two people to hand search about 500 m of river in a day. With eDNA surveys one person was able to survey across many sites in just three days. This would have probably taken weeks of work and a larger team if using traditional methods.
Sampling Techniques Made Easy
NatureMetrics worked with the Norfolk Rivers Trust team to deliver an aquatic eDNA survey, targeting White Clawed and Signal crayfish. We advised on sampling strategy and provided the eDNA sampling kits, which we processed in our laboratories. We then advised Norfolk Rivers Trust on data interpretation and considerations, helping to maximise the usefulness of the data.
Figure 1. The proportion of DNA sequences allocated to the two crayfish species (rows) in ten sampling sites (columns). The White Clawed Crayfish (WCC) is endemic to the UK, and the Signal Crayfish is an invasive species that is threatening the WCC. Each bubble per sample represents the proportion of DNA for each species for that sample. The size of the bubble is relative to the number of sequences from all species for that sample.
- NatureMetrics and NRT have now set up a long-term collaboration to monitor and track the native and invasive crayfish populations at key sites throughout the year and test the efficiency of eDNA in different seasons.
- Both parties are benefiting from this work, conserving key sites for endemic British crayfish and improving our understanding of the seasonal dynamics of crayfish eDNA in streams.
Evidence of Species Occurrences That Help to Manage and Conserve
The eDNA surveys identified populations of both species that had not been identified with traditional monitoring.
Notable detections included:
- A suspected-but-not-yet-found population of white-clawed crayfish that can now be actively protected.
- A population of signal crayfish in a site that had been thought safe but will now be ruled out as a reintroduction site to avoid wasting precious resources.
- Confirmed populations of white-clawed crayfish in two release sites, in an encouraging sign of the project’s success.
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