White-Clawed Crayfish Surveys
White-Clawed Crayfish & the Law
White-clawed Crayfish are the only native freshwater crayfish species present within the UK. Their claws are creamy or rosy white on the underside, giving them their name. The introduction of invasive non-native species of crayfish has led to the 50-80% decline of White-clawed Crayfish through direct competition and introduction of the fatal disease crayfish plague carried by introduced species. In addition, habitat loss and water pollution have had further impacts on the native crayfish. White-clawed Crayfish are fully protected under the Wildlife and Countryside Act 1981 (amended) and The Conservation of Habitats and Species Regulations (2017). This makes it an offence to kill or injure them as well as disturb them in/or destroy their habitat.
Typical habitat
White-clawed Crayfish live in rivers and streams (preferably base-rich) throughout the UK. However, due to the presence of invasive crayfish in Britain, their available habitat area has significantly decreased.
Basic requirements for White-clawed Crayfish survival include:
- Suitable refuges (e.g. stones)
- Food supply (e.g. leaf litter, macrophytes, aquatic invertebrates, fish remains)
- Access to other populations for breeding
- Good water quality
- No competition from non-native crayfish
- No crayfish plague (introduced by non-native crayfish)
Crayfish are susceptible to predation (particularly as juveniles and after molting), which makes suitable refuges of utmost importance. Refuges must be fully submerged, sizeable enough to cover crayfish, aerated, resistant to high water flows and available for occupation.
eDNA surveys
Environmental DNA or eDNA is a new technology for surveying for crayfish. Water samples are collected from the stream or river and sent to a special laboratory for DNA analysis. This method is much better for determining the absence of White-clawed Crayfish in a water body because it is quicker, less expensive, has a wider survey time window and is less invasive for the animals themselves.
However, eDNA cannot measure the estimated population of crayfish present, which is required for an EPS Licence. Therefore if the eDNA test is positive, further Phase II Surveys are required to inform a European Protected Species Licence application.
Phase II White-clawed Crayfish surveys
A Phase I survey does not require any licences to survey waterbodies. However, if White-clawed Crayfish may be present on the site, Phase II surveys may only be undertaken by a trained ecologist with a survey licence for them.
The standard method of surveying for White-clawed Crayfish is a manual search of potential refuges within the survey area. However, this method can only be undertaken where the water depth is no more than 60cm and it is safe to do so. Alternative methods such as trapping may also be used if the standard method is not possible but can be more invasive and labour-intensive. Surveys have a limited season and are best undertaken in July to September after they have released their young.
White-clawed Crayfish & development
Development that would impact populations and habitats of White-clawed Crayfish must include a detailed avoidance, mitigation, compensation and enhancement strategy. To meet planning policy, the development will only be allowed if it provides a net benefit to the species. Habitat restoration and modification of features to benefit White-clawed Crayfish may be used.