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Low‐ and high‐frequency sounds were tested as a means of repelling blueback herring Alosa aestivalis in confined‐area and open‐water experiments. Confined‐area tests were performed by analyzing the response of blueback herring in floating net‐pens to sounds differing in frequency, sound pressure levels (SPLs, given in decibels [dB] in reference to l.0 μPa), and pulse width. Highfrequency sounds between 110 and 140 kHz, at SPLs above 180 dB (at 1.0 m from the transducer) and at various pulse widths, elicited statistically significant (P < 0.05) avoidance responses by blueback herring. A reduced response was observed at sound frequencies of 100 and 150 kHz. Low‐frequency sounds between 0.1 and 1 kHz at SPLs of 160–175 dB (at 1.0 m from the transducer) elicited only short‐term startle responses. Field tests were performed at Richard B. Russell Dam (on the Savannah River at the Georgia‐South Carolina border) to evaluate candidate transducers and amplifiers. In field evaluations a single high‐frequency transducer emitting 124.6‐ and 130.9‐kHz sounds at an SPL of 187 or 200 dB (at 1.0 m) partially repelled blueback herring that were approximately 60 m away from the transducer for periods of up to I h. These results suggest that high‐frequency sound may provide an effective and inexpensive method, relative to structural measures, for reducing entrainment of blueback herring at hydropower stations.

Fish can sense a wide variety of sounds by means of the otolith organs of the inner ear. Among the incompletely understood components of this process are the patterns of movement of the otoliths vis-à-vis fish head or whole-body movement. How complex are the motions? How does the otolith organ respond to sounds from different directions and frequencies? In the present work we examine the responses of a dense rigid scatterer (representing the otolith) suspended in an acoustic fluid to low-frequency planar progressive acoustic waves. A simple mechanical model, which predicts both translational and angular oscillation, is formulated. The responses of simple shapes (sphere and hemisphere) are analyzed with an acoustic finite element model. The hemispherical scatterer is found to oscillate both in the direction of the propagation of the progressive waves and also in the plane of the wavefront as a result of angular motion. The models predict that this characteristic will be shared by other irregularly-shaped scatterers, including fish otoliths, which could provide the fish hearing mechanisms with an additional component of oscillation and therefore one more source of acoustical cues.