White-Clawed Crayfish Survey
Where water courses, lakes, reservoirs and water-filled quarries are deemed likely to be affected by project proposals, a white-clawed crayfish survey may be required, which aims to establish the presence/ likely absence of white-clawed crayfish on site, and identify potential for constraints and opportunities.
White-clawed crayfish are found within rivers, streams, canals, lakes and other standing water bodies throughout portions of England and Wales, though their populations are scattered and typically at low density. The British population has endured a long term decline, falling by approximately 70% since the 1970s, primarily due to a combination of habitat loss and degradation, and the introduction of the disease-carrying and predatory American signal crayfish. They are protected under UK law, making it an offence of kill, capture, or disturb them, though their habitat is not specifically protected. Works affecting white-clawed crayfish are subject to licensing procedures.
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The appraisal is used to inform the emerging scheme design, enabling significant ecological effects within the zone of influence to be avoided, mitigated, or compensated for, where necessary. This ensures the continued favourable conservation status of white-clawed crayfish, post development, and ultimately compliance with nature conservation legislation and planning policy.
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Presence/ likely absence surveys involve the systematic manual searching of five distinct patches of habitat throughout the survey area. A minimum of ten potential refuges are inspected within each patch, searching for evidence of white-clawed crayfish. The manual searches may be supplemented by torching surveys, whereby the banks of the water feature are traversed at dusk for a minimum of sixty minutes. The surveys encompass ecologically linked suitable habitat beyond the site. If white-clawed crayfish are identified, two additional manual searches with be required, to establish population density. The field survey is typically supplemented by a desk study, utilising maps and aerial photographs of the surrounding area to identify ecological connectivity, and published records of white-clawed crayfish, purchased from the local records centre.
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Alternatively, if the survey area comprises an enclosed water body, eDNA sampling may be undertaken. This involves a rapid assessment of presence/ absence within water bodies, based on traces of white-clawed crayfish DNA within the water column, which typically persists for several weeks. If a negative result is returned, instant confirmation of absence can be established and the feature can be scoped out of the study, thereby expediting the survey process. However, if presence if confirmed, further survey will be required to establish the population size, which eDNA sampling alone cannot determine.
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Requirements for any necessary avoidance, mitigation, or compensation measures will be identified, and opportunities for ecological enhancement will be outlined, to integrate on-site biodiversity net gain into the scheme at an early stage, where possible.​ If the proposals are deemed likely to adversely affect white-clawed crayfish, a mitigation licence may be required, prior to the commencement of works.
White-clawed crayfish surveys are seasonally constrained and protracted, making it prudent to plan ahead and consider ecological issues early on in the planning process. A robust white-clawed crayfish survey at an early stage in project planning and design can therefore deliver significant benefits, avoiding potentially costly and time-consuming delays.​
When
White-clawed crayfish presence/ likely absence surveys should ideally be undertaken between July-September inclusive, though surveys between April-October inclusive are permissible. eDNA sampling must be undertaken between April-October inclusive.
Why Us
With over fifteen years' experience in undertaking ecological surveys, mitigation design, licensing, site supervision, and monitoring, our team of expert ecologists can help guide your project through the planning process.
Our licensed ecologists can appraise your site's white-clawed crayfish suitability, undertake surveys, design mitigation strategies, and apply for mitigation licences.
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By working closely with our clients, we ensure that their developments progress smoothly and in full compliance with the law, orchestrating the best possible outcome for them and the natural world.
