Effectiveness of pulsed direct current at reducing walleye escapement from a simulated reservoir

Abstract

Fish escapement from reservoirs is problematic and makes management of these fisheries challenging. Historically, physical barriers have been used to limit fish movement but are prone to clogging and require constant maintenance. Thus, evaluations of alternative technologies are needed to limit reservoir fish escapement. Electrical barriers may offer an effective option for reducing fish escapement, but their effectiveness may be species-specific. Here, we predicted pulsed direct current with a graduated field would (1) alter walleye Sander vitreus behavior, (2) reduce escapement and (3) not induce mortality. Laboratory experiments compared walleye behavior, escapement, and mortality at four pulse (0, 0.3, 0.5, and 0.8ms) and three voltage (0, 60, and 80V) settings. The average voltage gradient 80cm in front of the outlet was 0.09V/cm (power density=1.36μW/cm3) at 60V and 0.14V/cm (power density=3.36μW/cm3) at 80V. Our results demonstrate that pulsed direct current was successful at reducing approaches and increasing deflections of walleyes, suggesting fish avoided the barrier. Altered behavior resulted in nearly an 80% reduction in escapement with smaller fish more likely to escape compared to larger individuals. However, pulse width and voltage did not influence escapement rates. Walleye mortality was 0% for control trials, ranged from 0.5–5.7% with the current activated, and was greatest at the highest barrier setting (0.8ms, 80V). Our laboratory results indicate pulsed direct current may be effective at reducing fish escapement from reservoirs. Lower pulse and voltage settings should be used due to their ability to reduce escapement while inflicting minimal mortality compared to higher settings. Additional work should evaluate the success of electric barriers in reservoir field settings under a wider range of conditions and on additional species.