Downriver Passage of Juvenile Blueback Herring near an Ultrasonic Field in the Mohawk River

Abstract

At the Crescent Hydroelectric Project (Crescent), New York, the Mohawk River is impounded by two dams separated by an island, which creates two channels; the turbine channel conveys water to the hydroelectric turbines, and the main channel conveys water around the turbines. Our objective was to determine whether ultrasound could be used to divert juvenile blueback herring Alosa aestivalis from entering the turbine channel during their fall downriver migration. Fixed-location hydroacoustics (420 kHz) was used to continuously monitor fish passage in the main channel upriver and downriver of the 122–128-kHz ultrasonic projectors. A relative index of abundance was derived from echo integration of acoustic backscatter collected from three horizontally aimed single-beam transducers sampling across each channel, while the proportion and speed of fish moving downriver were estimated from upward-facing split-beam transducers. The presence of juvenile blueback herring was verified by castnetting. Fish migrated downriver episodically for periods of hours rather than days. The mean daily number of downstream migrants (N_d ) in the main channel was estimated to be 4.2 times higher at the upriver site than at the downriver site. The estimate for N_d at the main-channel downriver site (N_DM ) was compared with the expected N_d (N_EDM ) based on the proportion of total river flow moving through the main-channel downriver site as measured by acoustic Doppler current profilers. The mean daily difference between N_DM and N_EDM was significantly different from zero. The estimated proportion of fish that passed the main-channel downriver site (31.3%) was almost three times greater than the proportion expected (11.5%). If it is valid to assume that water flow directly influences entrainment and impingement, then the significantly higher-than-expected number of blueback herring that migrated downriver in the main channel could be an indication that ultrasound at Crescent was partially effective in diverting fish.

Received July 17, 2011; accepted February 2, 2012

ACKNOWLEDGMENTS

This study was funded by the New York Power Authority (Contract Number 4600001920). Technical assistance received from K. Kumagai, B. McFadden, and P. Nealson (Hydroacoustic Technology, Inc.) was greatly appreciated. Data collection would not have been possible without the field assistance of T. Hoffman, M. Jeanneau, C. Porembski, and E. Sobo.