Grabowski, T. B., T. D. Ferguson, J. T. Peterson, and C. A. Jennings. 2009. Capture probability and behavioral response of robust redhorse, an cryptic riverine fish, to electrofishing. North American Journal of Fisheries Management 29:721–729.
Conservation and management of riverine species, such as robust redhorse Moxostoma robustum, can be hindered by incomplete understanding of their population status. Behavioral responses to sampling methodologies and susceptibility to capture with a particular gear type has implications to the reliability of population assessments, yet are rarely evaluated. Consequently, we used radio-tagged robust redhorse in the Ocmulgee River, Georgia, to estimate capture probability when sampled with standard boat-electrofishing techniques and assess behavioral responses of individuals to single and repeated exposures to electrofishing, which is the recommended sampling method for this species. Transects containing 1-8 radio-tagged individuals were sampled. The positions of radio-tagged individuals were recorded prior to 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 a repeated sample in time. Only one radio-tagged individual and six untagged individuals were captured after 7.46 h of effort. Radio-tagged robust redhorse did not exhibit an immediate response to boat electrofishing. Some movement away from their original position was observed in radio-tagged robust redhorse within the first hour post-electrofishing (mean ± SE: 0.15 ± 0.05 km; range: 0.0-0.80 km), after 24 h (0.19 ± 0.05 km), and after 3-5 days (0.23 ± 0.14 km). However, this movement was similar from that exhibited by fish located at similar intervals during a related telemetry study without exposure to electrofishing. A mean capture probability of 0.031 with 95% Bayesian credibility intervals of 0.002-0.111 was estimated from the best approximating model. Electrofishing is not a particularly effective method for capturing this species; therefore, inferences about population size and distribution of this 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.