Surveying is carrying out a field survey to detect crayfish and/or estimate their abundane. The extent and intensity of effort depend on the purpose of the survey and the level of confidence required, e.g. is the aim to detect a crayfish population which is present at low abundance? Is detection of crayfish presence enough, or is a semi-quantitative estimate of abundance needed as a basis for monitoring? Monitoring is surveying a crayfish population at intervals (often with environmental factors), to assess whether there is any change in conditions or status in a spatial area over time.
Whether conducting baseline surveys or monitoring known crayfish populations there is no one fixed survey method that is ideal for all situations. The most appropriate method or methods to use depends on the type of habitat present and the purpose of survey. For example, how much confidence is required about presence/absence, or how much detail on abundance is necessary. Use the resources below to understand the application and the limitations of each method, and choose the most appropriate method in relation to your local conditions.
Standard survey methods include:
- Manual search
- Kick and sweep
- Conventional traps (i.e. baited traps)
- Artifical refuge traps
Also a good first step before starting survey work is an assessment of habitat potential for crayfish, but note that non-native crayfish may be present in sites unsuitable for White-clawed crayfish, due to greater tolerance of temporarily dry conditions and poorer water quality. Also look out for field signs ”surrogates” for survey – carapace remains from predation by otter, mink, heron, also crayfish burrows (also bycatch records from angling and electrofishing).
Peay S. (2004) Keynote a cost-led evaluation of survey methods and monitoring for White-clawed crayfish – lessons from the UK. Knowledge and Management of Aquatic Ecosystems 372-373 335-352. Link to free access journal
Peay S. (2003) Monitoring the White-clawed crayfish Austropotamobius pallipes. Conserving Natura 2000 Rivers Monitoring Series No. 1. English Nature, Peterborough. Link to free access report
Lang M. & Wylde A. (2000) Some observations on surveying native and Signal Crayfish. British Wildlife 11(6) 398-400.
The University of Nice is developing a database for field identification of crayfish in Europe which will be availble as an app to download. Link to crayfish key