White clawed crayfish

Thomson Ecology employs knowledgeable invertebrate specialists who can advise you on white clawed crayfish surveys and conservation.

Ecology and conservation status

The white clawed crayfish (Austropotamobius pallipes) is Britain’s only native freshwater crayfish. It is readily identified by its whitish underside, and has a brown or olive body with a pitted appearance. Adults can be as long as 12 cm. Adult males have bigger claws than females and are more territorial during the breeding season from September to November. They can live for more than 10 years, reaching sexual maturity at 4 years. Females over-winter with eggs held under their tails, releasing juveniles at the beginning of June. The species is nocturnal, living under rocks or submerged logs in the day, and feeding on worms, larvae, snails and small fish in the night.
The white clawed crayfish occurs in streams, rivers, lakes and canals in some parts of the UK but its numbers have declined -largely due to competition from the introduction of the North American signal crayfish in the 1980s and the fungus that it carries (crayfish plague) but also due to loss of habitat through flood defence works, construction, dredging and agricultural activities.

Protection and legislation

The white clawed crayfish is listed under Annex II of the Habitats Directive and therefore member states are required to designate Special Areas of Conservation to protect important populations of this species.

Outside designated sites, white-clawed crayfish receive partial protection under the law. It is prohibited to commercially harvest or capture white-clawed crayfish without a licence but the legislation does not provide strict protection of individual crayfish or their habitats specifically (although their habitat is usually indirectly protected through other legislation such as the Water Framework Directive).

The white clawed crayfish is also a Priority species in the UK Biodiversity Action Plan and is a Species of Principal Importance in England under Section 41 of the NERC Act 2006 (section 42 in Wales) and the Nature Conservation (Scotland) Act in Scotland. It is government policy that local authorities consider the conservation status of such species when determining planning applications.

Licences and surveys

Surveys of white clawed crayfish populations involve setting funnel-shaped traps containing bait along the banks of streams, manual and torchlight surveys. A relevant licence held by a qualified ecologist is required to trap this species for survey purposes and a separate licence from the Environment Agency is required for the use of crayfish traps under the Salmon and Freshwater Fisheries Act.

Mitigation

There are a number of ecological mitigation techniques that can be employed depending on the scale of the development and how it will impact on the white-clawed crayfish population. One of the key things to ensure is that the crayfish have a suitable habitat both during and after the development. They are very sensitive to pollution and vulnerable to crayfish plague, a disease which can be spread by dirty construction equipment. All equipment should therefore be properly disinfected, cleaned and dried when moving from site to site. Following major projects, post-project monitoring of populations should be carried out and remedial action taken if numbers decline.