Silver Carp herding: A telemetry evaluation of efficacy and implications for design and application

Objective: The removal of invasive Silver Carp Hypophthalmichthys molitrix is a primary control action in North America. Strong avoidance responses to underwater sound and electricity have been shown to facilitate herding and mass removal of these fish. We conducted a telemetry study on a closed population of Silver Carp (i.e., 10 telemetered fish) to assess fine-scale movement responses to herding stimuli. Methods: Two herding boats traveled along bank-to-bank transects through the study area (longitudinal progression rate = 0.37 m/s) emitting sound and electricity ("combination technique") or no added stimuli ("control"). Result: The combination technique was most effective in terms of increasing fish presence (2.2 x the control) in the refuge zones when herding had concluded and effective range (i.e., fish reaction distance; 1.6 x the control) relative to the herding boats. The median (similar to 1 m/s) and maximum (similar to 2 m/s) swimming velocity was relatively stable across fixed effects, except for the negative influence of water depth on maximum velocity. Water depth also exhibited a negative effect on fish reaction distance. Conclusion: Our results suggest that the effective range of the combination technique was conservatively 200 m (similar to 20 dB re 1 mu Pa > ambient level) when accounting for water depth in the study area. Herding deployments <1 m/s (longitudinal progression) could control fish passing and maintain fish movements toward an intended location. The information provided herein can serve to assist planning, designing, and applying herding efforts to manage, control, and remove these invasive fish.