The White-Clawed Crayfish (Austropotamobius pallipes) is the only native freshwater crayfish species in Great Britain although many other crayfish species such as the American Signal Crayfish (Pacifastacus lenuisculus), Narrow Clawed (Turkish) Crayfish (Astacus leptodactylus) and the Noble Crayfish (Astacus astacus) have now been intentionally and accidentally introduced into our rivers and streams for commercial purposes of crayfish farming and have resulted in a significant decline in the native species through out-competing and the spreading of pathogens.
This decline has led to the White-Clawed Crayfish being protected under both British and European law. The White-Clawed crayfish is listed on Schedule 5 of the Wildlife and Countryside Act 1981 (as amended) and is also included in Appendix III of the Bern Convention and Annexes II and V of the European Habitats and Species Directive. It is also a priority species under the UK Biodiversity Action Plan (BAP).
The species current stronghold is in many areas of central and northern England, where they can still be found in relative abundance. Former White-Clawed Crayfish strongholds such as the chalk streams of south-east England now only hold scattered and isolated populations. The distribution of the White-clawed Crayfish in Wales is mainly confined to two river catchments, the Usk and the Wye. Areas of the north and west Wales appear to not support the native species, due primarily to the fast flowing upland areas and high levels of acidity in the river catchments.
If development works are planned to be completed within, or at close proximity to a watercourse or waterbody, it is important to determine if White-Clawed Crayfish or invasive crayfish species are present and whether the proposed works will impact on the species and their potential distribution.
All of our surveys are conducted by a suitably qualified ecologist with an appropriate Natural England or Natural Resources Wales crayfish license.
Often the first stage of a project is to undertake a background search to determine if there are records of crayfish in the river catchment. Typically this will involve contacting the relevant local records centre and statutory agencies.
The survey for crayfish involves three main methods:
This crayfish survey technique involves walking along a watercourse and includes taking samples from potential refuges and completing a habitat assessment. Several samples may be required to be able to establish a population estimate. Where appropriate, kick sampling using a pond net is also used.
Areas of boulders and cobbles in shallow water are searched by hand and occasionally with the use of a glass-bottomed bucket. Stones are carefully turned over and after the silt has settled the substrate can be viewed and any crayfish captured for examination. Stones are then replaced afterwards. A pond-dipping net is often placed downstream to catch any escaping crayfish. In addition, root systems under bankside trees are also searched.
This crayfish survey method involves recording crayfish via torchlight at night.
A successful method uses baited traps that are left for no longer than 24 hours at a time. This method although successful can harm non-target species such as otter and water vole; therefore trapping may not always be appropriate.
Another crayfish survey technique involves using baited traps that are left overnight and retrieved the next day. The traps are often used in areas such as deep pools that are not suitable for hand searching. These baited traps are secured using metal stakes and string.
White-clawed crayfish surveys are predominantly carried out between March to September inclusively, however between April and June surveying (other than torching at night) is not advised as it is likely to cause harm to the young.
Our ecologists are able to undertake crayfish surveys. For more information call us on 029 2065 0331.