Fixed and Mobile Hydroacoustic Detection of Juvenile Blueback Herring to Assess Avoidance Behavior of Ultrasonic Deterrent

Juvenile blueback herring, Alosa aestivalis, downstream migration requires passing the Crescent Hydroelectric Project, Mohawk River, New York.  An ultrasonic system is in place to deter blueback herring from approaching the power plant.  During the 2008 fall outmigration, the abundance of fish passing two fixed locations on the main channel upriver (UM) and downriver (DM) of the ultrasound source was continuously monitored using horizontally-aimed and upward-looking transducers.  Flow was also monitored using an acoustic Doppler current profiler (ADCP).  Data from the fixed-locations was supplemented by a vessel-mounted echosounder with horizontally- and vertically-aimed transducers, as well as, ADCP that traversed multiple locations.  The fixed-location transducers were well situated to monitor passage of fish through UM and DM, based on the distribution of fish observed with the vessel-mounted transducers.  The percentage of fish at UM that passed through DM (31.3%) was almost three times greater than that expected (11.5%) based on the proportion of water volume that passed through DM compared with the volume of water that passed through the power plant.  The most plausible explanation for the difference between the observed and expected values appears to be the presence of ultrasound to steer juvenile blueback herring away from the power plant.  Adjusting the direction and intensity of the ultrasonic field is predicted to increase the blueback herring avoidance behavior.