Capture Probability and Behavioral Response of the Robust Redhorse, a Cryptic Riverine Fish, to Electrofishing

Conservation and management of riverine species, such as the robust redhorse Moxostoma robustum, can be hindered by incomplete understanding of their population status. Behavioral responses to sampling methods and susceptibility 10 Capture by it Particular gear type have implications for the reliability Of population assessments yet are rarely evaluated. Consequently, We used radio-tagged robust redhorses in the Ocmulgee River. Georgia, to estimate capture probability when sampled with standard boat electrofishing techniques and to assess behavioral responses of individuals to single and repeated exposures to electrofishing. the recommended sampling method for this species. Transects containing one to eight radio-tagged individuals were sampled. The positions of radio-tagged individuals Were recorded before electrofishing and at 1-h, 24-h, and 3-5-d intervals after sampling. We estimated robust redhorse abundance and capture probability by treating each transect as analogous to it repeated sample in time. Only one radio-tagged individual and six untagged individuals were captured after 7.46 h of effort. The radio-tared fist id not exhibit an immediate response to boat electrofishing, but some did move horn their original position after electrofishing. Mean movement was 0.15 km after 1 h, 0.19 km after 24 h, and 0.23 km after 3-5 d. However, this movement was similar to thin exhibited by fish located at similar intervals during it related telemetry study without exposure to electrofishing. A mean capture probability of 0.031 with a 95% Bayesian credibility interval of 0.002-0.111 was estimated front the best-approximating model. Electrofishing is not a Particularly effective method for capturing this species: therefore, inferences about population size and distribution Of (his or other cryptic species need to account for low detection probabilities associated With electrofishing. Alternative approaches or Multiple strategies should be considered when assessing the status of such Species.