Practical techniques: White-clawed crayfish
England, Wales, Northern Ireland and Ireland
The white-clawed crayfish (Austropotamobius pallipes) is the UK’s and Ireland’s only native freshwater crayfish. It is in decline due largely to competition from the introduced North American signal crayfish (Pacifastacus leniusculus) which also carries a fungus (crayfish plague) that can wipe out populations of white clawed crayfish in a matter of weeks. Habitat loss and damage due to flood defence works, construction, dredging and agricultural activities are also contributing to the decline.
Protection and its implications
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. These sites are protected under the the Habitats Directive and associated Regulations.
Outside designated sites, white-clawed crayfish receive limited protection under the Wildlife and Countryside Act 1981 (as amended), the Salmon and Freshwater Fisheries Act and the Wildlife (Northern Ireland) Order 1985 (as amended by the Wildlife and Natural Environment Act (Northern Ireland) 2011). This protection is intended to prevent commercial harvesting of white-clawed crayfish and prohibits their capture without a licence. This legislation does not provide strict protection of individual crayfish or their habitats specifically, although their habitat receives some protection as a result of regulations derived from the Environmental Liabilities Directive, and less directly, the Water Framework Directive.
The white clawed crayfish is a priority species in England, Wales, and Northern Ireland. Government policy is that local planning authorities should consider such species when determining planning applications. Consideration of priority species would also be expected in the UK as part of the legal Biodiversity Duty.
Typically, the policies of local planning authorities do not distinguish between fully protected species and partially protected species, such as white-clawed crayfish. If this species is present on a development site, it could be a reason for refusing planning permission unless the applicant can clearly demonstrate that the species will be adequately protected during the development process, that disturbance is kept to a minimum, and adequate alternative habitat is provided to sustain at least the existing population. Whilst white-clawed crayfish and their habitats are not strictly protected, the combination of their status as a priority species and the lack of distinction that local authorities make between fully and partially protected species, can mean that planning conditions lead to the treatment of white-clawed crayfish on development sites as if they were a fully protected species.
The white-clawed crayfish is only likely to be an issue on development sites which are close to water, particularly rivers and streams. Further, white-clawed crayfish is now absent from many parts of the country and so this species may not be a consideration even when a water body is directly affected by development.
Mitigation techniques
Protecting individual crayfish
White-clawed crayfish are sensitive to pollution. For developments potentially affecting water bodies containing this species, it is important that pollution is controlled both during and after construction. The Environment Agency has produced a series of Pollution Prevention Guidelines which should help with this issue. The guidelines have been officially withdrawn but provide useful information nevertheless. White-clawed crayfish are also vulnerable to crayfish plague, a disease which can be spread by dirty construction equipment. Equipment used in rivers should therefore be properly disinfected, cleaned and dried when it is moved from site to site. For longer stretches of development works affecting watercourses, it may be best to work in a downstream direction to avoid spreading the disease.
The best way to protect white-clawed crayfish during the development process is likely to depend on the scale and type of the works. Any action which involves the capture and handling of white-clawed crayfish will require a licence from the appropriate statutory agency. In the England and Wales, a separate licence is required for the use of crayfish traps under the Salmon and Freshwater Fisheries Act.
For small scale works, such as repairs to bridges and culverts and short lengths of bank reinforcement, it may be sufficient simply to search for and remove individual white-clawed crayfish from the area affected by the works just before works commence.
For medium scale works, such as replacing bridges or culverts and longer lengths of bank reinforcement that will not involve removing the water from the channel, it may be appropriate to exclude crayfish from the works area. In shallow and clear water, this can be done by searching for and removing crayfish and their refuges just before construction commences. Undertaking some of this work at night may improve capture rates. In deeper and more turbid water, it may be necessary to rely on crayfish traps. However, trapping efficiency is rather low and many traps may need to be used over several nights. Care must also be taken to avoid trapping water voles.
Wire mesh or similar may be used to help prevent crayfish from returning to the works area. However, this requires careful installation and constant maintenance in order to be effective. An alternative approach might be to carry out works on the channel bed or banks in short sections rather than all at once, with each area searched thoroughly for crayfish as the works progress.
For operations involving channel diversion or otherwise removing the water from part of the channel, it is likely that crayfish will need to be excluded from the area. An effective method is to drain down the channel a few days before works begin and then systematically to search the dry channel bed for crayfish, collecting them in buckets to be transferred to alternative habitat. The exercise should be repeated until no more crayfish are found. Leaving the channel dry overnight can be useful. If pumps are used, then a screen over the extraction hose can prevent crayfish being sucked into the pump.
When crayfish are excluded from the works, they usually recolonise naturally once the works are completed, even from several hundred metres away, as long as the habitat is suitable for them.
Maintaining crayfish habitat
Perhaps more important than protecting individual crayfish is ensuring that alternative habitat is provided following the development.
Crayfish require refuges for shelter, firstly from predators during the day and secondly to avoid being washed downstream in times of high flow. The provision of suitable refuges is therefore critical when habitats are restored or new habitats are created. Suitable refuges may be created by reinstating boulders taken from the stream bed and creating gaps amongst stone revetments or other material reinforcing the bank. Willow piling and planting trees close to the watercourse may also lead to the creation of suitable refuges over time. If a new channel is being created, sections of vertical bank and areas of low flow should be included in the design. Moderate amounts of submerged aquatic plants should also benefit crayfish.
Other factors to consider include good water quality, adequate food supply, connectivity with other populations of white-clawed crayfish, preventing colonisation by non-native crayfish, stopping the spread of crayfish plague, and controlling silting and pollution.
Post-development monitoring
Following major projects, there may be a requirement to monitor populations of white-clawed crayfish so that remedial action can be taken if the population does not re-colonise the area. Monitoring results will also inform mitigation for future developments. This may take the form of an annual survey using the same methods as in the preliminary site investigations so that the results can be compared.
Timing of works
Trapping, handling or moving of white-clawed crayfish should not be carried out during crayfish breeding (May to July) or wintering (November to February) periods.
Further reading
Peay, S. (2000) Guidance on Works affecting White-clawed Crayfish. Scott Wilson Resource Report for English Nature Species Recovery Programme.
Peay, S. (2003) Monitoring the White-clawed Crayfish Autropotamobius pallipes. Conserving Natura 2000 Rivers Monitoring Series No. 1. English Nature, Peterborough.
Peay S., Kindemba V., Attwood F. and Christmas M. (2011). A toolkit for developing catchment-scale conservation strategy for White-clawed crayfish. Version 1 October 2011 Buglife – The Invertebrate Conservation Trust, Peterborough.
Natural England (2015) White-clawed crayfish: surveys and mitigation for development projects. https://www.gov.uk/guidance/white-clawed-crayfish-protection-surveys-and-licences