Development of Standardized Stream-Dwelling Crayfish Sampling Methods at Site and Drainage Scales

Methods for assessing stream fish, freshwater mussel, and insect assemblage structure, presence, and status have existed for several decades. Such methods are lacking for assessing crayfish. The current study addresses that deficiency by testing robust sampling methods to assess species richness, distribution, and density at both site and drainage scales. We tested the ability of timed search methods to capture all known species of crayfish at a site and of a kick seine to assess the mean density of crayfish (per m2) in riffles. Riparian crayfish burrows were excavated to capture additional species not captured with the other methods. Our data and methods allow for assessments of the inherent trade-off between sampling time and resources and statistical confidence. An example sampling regime of 3.5 h of effort per site required seven 15-min timed search samples and captured at least 80% of the crayfish species richness, with 85% confidence across all sites tested. Twelve kick-seine samples yielded crayfish density estimates within 50% of an estimated true density at 70% confidence for all species with densities >0.5/m2. In the drainage-scale component, we employed a sampling effort prescription derived from our site-scale data across seven drainages in Missouri. To achieve 100% of the species richness sampled at 97.5% confidence in wadeable second- to fourth-order streams, researchers will need to sample one site for every 18 river kilometers of second- to fourth-order streams occurring in a drainage. We believe our methods can provide a repeatable and statistically supported tool for researchers assessing crayfish assemblages in wadeable streams across the Midwest.