Application of electricity and underwater acoustics to clear fish from a navigation lock during maintenance

The presence of fish within navigation locks can introduce an environmental challenge for construction crews when maintenance is required. This study examined the effectiveness of a dual-deterrent fish herding technique using electricity and acoustic stimuli to reduce the abundance of fish within a navigation lock before a scheduled dewatering for maintenance. Fixed-location multi-beam imaging sonar was used to evaluate fish per minute (FPM) detections near the lock entrance before, during, and after the herding effort. Standardized mobile side-scan sonar surveys were also conducted before and after the herding to examine fish presence throughout the entire lock. Collectively, a 73% reduction in fish targets detected by side-scan sonar and a 43% reduction in FPM detected by imaging sonar were observed following the herding technique. Post-fish herding, an 88% reduction in FPM > 400 mm and a 35% reduction in FPM < 400 mm were observed. Fish abundance within the lock chamber was reduced and did not result in construction delays, which was problematic and costly during previous dewatering events. Because data from this study are limited to a single lock dewatering and fish clearing event, caution is warranted with the extrapolation of these results. However, the applied methods show promise and may inform future fish clearing efforts to aid lock maintenance.