Investigating Sources of Bias in Freshwater Mussel Sampling Methods in the Meramec River Basin, Missouri

Freshwater mussels are among the most threatened aquatic fauna in North America. Given the need for continued monitoring of threatened populations, an evaluation of the effectiveness of metrics from visually-based sampling methods is an essential step in assessing populations of these mollusks. We surveyed 14 sites in the Meramec River Basin in East Central Missouri. At each site, we employed three visual methods for estimating abundance; timed visual searches, systematic strip transects, and stratified randomly placed visual 0.25 m² quadrats. We excavated substrate at each 0.25 m² quadrat to determine baseline abundances for each species. When direct estimation of sampling efficiency is not possible, as is the case with timed visual searches and strip transects, investigation of method covariance, and the habitat-mediated bias associated with those methods, allows calibration of CPUE and density estimates. We compare the results of abundance estimates of each of the visual methods with the robust estimates based on excavated quadrat samples. Sampling effectiveness of visual-based methods were calculated and used to determine if visual techniques provide reasonable approximation of overall mussel abundances and investigated factors that influenced their effectiveness. These results will be used to produce sampling protocols for freshwater mussels for Missouri.