White Clawed Crayfish Surveys

Background

The white-clawed crayfish (Austropotamobius pallipes) is Britain’s only native species of crayfish. It will occupy a variety of habitats including streams, rivers, brooks, reservoirs and water-filled quarries. Although abundant in some waterbodies, the white-clawed crayfish has seen a dramatic decline in population in recent decades, primarily due to the presence of non-native species, including the North American signal crayfish (Pacifastacus leniusculus) that can carry a disease known as ‘crayfish plague’. Due to the risk of spreading disease, EMEC practice strict biosecurity standard in all our fieldwork.

Due to the decline in white-clawed crayfish numbers, it is now 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 (as amended) 20, as well as other legislation relating to rivers and fisheries. It is also a Priority Species under the UK Post-2010 Biodiversity Framework. Therefore, if development works are proposed within, or in close proximity to a suitable waterbody, it is important to determine if white-clawed crayfish are present and whether the proposed works will impact on the species.

Timing

White-clawed crayfish surveys can be carried out between July and September inclusively, avoiding suboptimal winter months and spring/autumn when crayfish carry eggs and young. A torchlight survey may be undertaken between April and June; however, other survey techniques are not advised during this period as it is likely to cause harm to the juvenile crayfish. Environmental DNA (eDNA) surveys can be carried out between April and October inclusive, when crayfish are likely to be most active.

Methodology

Depending on the nature of the site and its location, the local biological record centre may initially be contacted to see if there are records of crayfish within the waterbody that may be impacted by the works. Even when there are records of white-clawed crayfish in a watercourse, they are not uniformly spread along the channel and therefore a survey of crayfish presence and population must be conducted on site by a suitably qualified ecologist with an appropriate Natural England crayfish licence.

A white-clawed crayfish survey will be conducted in the watercourses on and around the site, and will involve refuge sampling, night viewing and trapping. Refuge sampling involves searching potential refuge locations within a watercourse, kick sampling using a pond net may also be undertaken where suitable. Night viewing involves searching for crayfish within a watercourse via torchlight at night. Trapping is a more invasive method and as such is generally only used where other methods are unsuitable.

The survey will be carried out by an appropriately licensed ecologist with an assistant for health and safety when working near water.

Environmental DNA Survey

Environmental DNA (eDNA) testing is a recognised survey technique for establishing the presence or absence of white-clawed crayfish in watercourses. Water samples will be taken from suitable watercourses within or surrounding the Site. The surveys will follow the eDNA methodology and protocol guidelines:

• The survey will be undertaken by a suitably experienced ecologist with an assistant for health and safety when working near water;
• Testing kits will be sourced from one of the Natural England approved agencies, e.g. ADAS, Sure Screen Scientifics
• Water samples will be taken between mid-April and late-October.

Please note, negative results returned from water samples taken outside of this period may not be accepted by the relevant local planning authority (LPA) and / or statutory body. Full white-clawed crayfish surveys may be required if the eDNA results return a positive result (which would incur additional costs).

Refuge Sampling

The standard survey method used to search for crayfish along a watercourse involves selectively searching potential refuges via stone-turning and using a net at several sample locations within the waterbody and completing a habitat assessment. Several sample locations may be required to establish a population estimate (although normally the primary purpose of the survey is to establish presence or presumed absence).

Night Viewing

This method involves recording crayfish via torchlight at night. This method results in minimal disturbance to the watercourse, covers a wider area and also covers inaccessible areas compared to manual searches such as refuge sampling.

Crayfish Trapping

A passive method using baited traps that are left in situ for no longer than 24 hours at a time. Traps are set in the evening and then retrieved the following morning and any captured white-clawed crayfish are identified and counted before release. This method requires consent from the Environment Agency. Only ‘otter friendly’ traps are used.

The survey will also take note of any invasive, non-native species present within the water, such as signal crayfish (Pacifastacus leniusculus) and aquatic plants.

Following the Survey

Report

We will provide a report detailing the results of our survey and any required mitigation as soon as possible following the survey, however; should you have a specific date for submission of a planning application we will do our utmost to accommodate this.

Licensing and Mitigation

Should white-clawed crayfish be present within or in close proximity to a development site, where it is likely that the crayfish will be either disturbed, injured or killed by the proposed works, it may be necessary to translocate the crayfish i.e. moving the white-clawed crayfish from the area to be affected into safe areas of suitable habitat. This will require a conservation licence from Natural England that will require detailed mitigation, compensation and enhancement measures to ensure no adverse impacts to this declining species.

Should a licence be required, EMEC Ecology can apply for this on a client’s behalf. EMEC Ecology has the ability to design and implement site-specific mitigation, compensation and enhancement measures that will be suitable for a planning application.

Monitoring

Monitoring the impact of development works is an important part of conservation and should it be required (it is often a stipulation of a licence), EMEC Ecology can monitor the site to see how effective the mitigation has been.