White-clawed Crayfish Surveys

The white-clawed crayfish is protected under Schedule 5 of the Wildlife and Countryside Act 1981 (as amended) making it illegal to harm, disturb and take (including to handle), this species without an appropriate licence, or to buy or sell white-clawed crayfish whether alive or dead.

It was once a widespread species in streams, rivers and lakes throughout England and Wales but, over the past 30 years, populations of the white-clawed crayfish have been decimated by the spread of non-native crayfish species and crayfish plague, a disease carried by the introduced North American signal crayfish. In some places the mismanagement of rivers has caused stretches to be less suitable. Industrial pollutants and sewerage have also taken their toll and few strongholds now remain.

All remaining populations are extremely vulnerable to extinction. It has been estimated that, if current trends continue, the species is likely to become extinct within 30 years. It is classified as Endangered on the IUCN Red List.

White-clawed crayfish spend most of the day under large stones or in the banks of rivers and lakes. They are largely nocturnal, emerging to feed on a broad diet of detritus, animals and plants. Breeding takes place in autumn. The eggs develop whilst attached to the mother’s abdomen, and the female overwinters with the eggs attached to her. They overwinter in burrows or other sheltered places and begin to look for food when the water warms again. The eggs usually hatch in June and the juveniles remain attached to the mother for about two weeks before becoming independent at the beginning of summer.

Expert crayfish consultants - white-clawed crayfish surveys

In order to inform licensing for projects you should consider the potential for impact on white-clawed crayfish. This may be direct (e.g. through river management works) or indirect (e.g. via discharge of water into watercourses). Our crayfish experts are able to assess the habitats present within water bodies for their potential to support white-clawed crayfish. This would usually be done as part of a Preliminary Ecological Appraisal (PEA) during the initial stages of the project. Potential presence is based on a number of habitat factors combined with historical records for white-clawed crayfish and non-native species.

If it is necessary to undertake a direct survey for white-clawed crayfish it would be based on the ‘Standard Method’ devised for monitoring white-clawed crayfish on behalf of Life in UK Rivers (Conserving Natura 2000 Rivers). Where the standard method is not practical, due to local conditions, then appropriate methodologies will be substituted, potentially including bait trapping, refuge trapping, night viewing, hand searching and burrow inspection. Our expert team possess the relevant licences for this work. In addition one of our team is licensed and qualified to carry out both bankside and SCUBA diving surveys. We can therefore, undertake underwater hand-searching surveys for this species, a method particularly useful in assessing populations across large bodies of water or in deep water (i.e. quarries and lakes).

Surveys for white-clawed crayfish should take place ideally between July and October inclusive. Valid surveys can be undertaken outside of this period, in warm weather in late spring or early autumn if necessary, but there is a risk of causing females to shed their eggs/young which should be acknowledged and controlled by careful handling.

The Ecology Consultancy has rigorous biosecurity procedures to ensure that our team do not transfer crayfish diseases, non-native animals or plants between sites.