White-clawed Crayfish Surveys and Mitigation

Durham Wildlife Services Ltd has many years experience in surveying white-clawed crayfish, creating and implementing mitigation measures for this species and obtaining the licence required to carry out these operations.

White-clawed crayfish have declined to such an extent that they are considered 'globally threatened' by the IUCN. They are protected under Schedule 5 of the Wildlife and Countryside Act (1981 as amended) making it illegal to intentionally kill, injure or take them form the wild and is also illegal to sell, possess or offer this species for sale.

The species is also listed under annexes II and V of the EC Habitats Directive, 1992, and this species is classed as a priority species within the subject of a UK Biodiversity Action Plan.

Initial Assessment

Habitat assessments can take place at any time of the year but surveys can only take place from mid June to the end of September to ensure females are not disturbed whilst carrying their eggs.

A habitat assessment will involve evaluating the potential value of river habitats for crayfish and the creation of an annotated map of favourable and unfavourable crayfish habitat locations along the affected stretch of a river.

The main survey technique is active searching in a suitable habitat to determine presence or absence of crayfish; however this is only possible during times of base flow in streams. This type of survey will involve:

• Searching under stones.
• Sweep netting in vegetation and under tree roots.
• Estimating population density.

An alternative survey method involves night searches by torchlight which involves:

• Recording crayfish active at night, these tend to be predominantly adults.
• Surveying more of the watercourse compared to manual searches.
• Viewing crayfish which use inaccessible refuges by day.
• Providing a quick estimate of the density of active animals.

Trapping is the only way of finding out if crayfish are present in watercourses which are too deep or turbid for manual searches, trapping surveys involve:

• Using a plastic mesh trap with a funnel entrance baited with scraps of fish or even cat food which are inspected the next day after setting.
• Only catch a low number, especially larger active males

A license will be required from Natural England to carry out these surveys and all work will be carried out by a competent ecologist with relevant skills, knowledge and experience of working with white-clawed crayfish.

Licensing

Any activity likely to contravene legislation in regard to protected white-clawed crayfish populations will require a license. Applications for licenses must be submitted to Natural England by a competent ecologist, i.e. a person able to demonstrate to the satisfaction of Natural England that they have the relevant skills and knowledge of the species concerned.

Mitigation

In areas where white-clawed crayfish are present and work needs to be carried out, all practical measures must be carried out to avoid or minimise the impacts on white-clawed crayfish. The project should aim to ensure the long term survival of the resident breeding population; once the work has been carried out, the habitat should remain suitable for crayfish in the long term. Depending of the type of project the following mitigation measures may be required:

• Minimise the amount of disturbance to the river bank.
• Minimise the length of channel affected.
• Where feasible bank and channel work should be carried out in small sections rather than all at once.
• Install measures to minimise siltation.
• Prevent any pollution of water courses.
• Provide a replacement habitat for the crayfish if the work involves a permanent loss of habitat.
• Include aquatic and emergent vegetation in channel design.
• If relocating crayfish a suitable habitat prepared in advance will be required.