Importance of Ultrasonic Field Direction for Guiding Juvenile Blueback Herring Past Hydroelectric Turbines

At the Crescent Hydroelectric Project (Crescent) on the Mohawk River, New York, ultrasound was produced to deter out-migrating Blueback Herring adults and juveniles to sea from entering the intake channel to the Crescent headrace and turbines where mortality may occur. To increase the previously reported deterrence rate, the sound field was extended further upriver to expose juvenile Blueback Herring to an increasing sound gradient as they migrate downriver and allow them more time to avoid the intake channel.  During the peak migration period of 20 September through 14 October 2012, data from continuous fixed-location horizontal echosounding indicated 77% of the net downstream passage of juvenile Blueback Herring at the upriver site bypassed the intake channel. This was significantly higher than expected assuming that entrainment is proportional to river flow, and higher than the proportion observed in presence of the previous ultrasound field.   Repeated pelagic trawling and mobile echosounder surveys corroborated these results by showing Blueback Herring density was significantly higher in the main channel than in the intake channel.  These statistically significant results demonstrate improved downstream passage at Crescent for the majority of out-migrating juvenile Blueback Herring.