Response of Out‐Migrating Adult American Shad Guided by Spill and Ultrasound as They Approach Rivière‐des‐Prairies Hydroelectric Generating Station (Québec, Canada)

Abstract Fish entrainment and mortality at hydropower generating stations constitute a major concern for power producers and government agencies. The American Shad Alosa sapidissima is particularly at risk at higher latitudes because of the large percentage of repeat spawners and the vulnerability of many populations. Total or partial turbine shutdowns at powerhouses and concurrent increased spillage are generally considered an effective way to enable fish to bypass the turbines and to reduce associated mortality, but this strategy is unappealing to hydropower producers because of the loss of power generation revenue. Two approaches were tested to repel out‐migrating adult American Shad from the turbine intakes of the Rivière‐des‐Prairies Generating Station powerhouse and guide them toward the adjacent spillway. The first approach consisted of shutting down the powerhouse and increasing spillage. The second approach consisted of testing the effectiveness of an ultrasonic field to deter American Shad from getting close to turbine intakes and to guide them toward the partially opened spillway. On average, fish density observed in front of the 54‐MW powerhouse was reduced by 93% as a result of a powerhouse shutdown lasting about 1 h and a concurrent spillage increase. Similarly, our results showed a decrease in shad abundance of 78–90% in front of the turbine intakes when a pulsed ultrasonic field (125 kHz) was activated. Measurements of sound pressure levels (SPLs) in the forebay suggested that the deterrent effect could be perceived by American Shad more than 100 m away, before they could sense higher water velocities near the powerhouse intakes. These results indicate that the combination of high‐SPL pulsed ultrasounds (125 kHz) and the concurrent opening of adjacent spillway gates could guide postspawn American Shad away from powerhouse intakes.