Effects of Mid-Frequency Sonar Signals on Alewife, Narragansett Bay, Rhode Island

This study investigated the effects of mid-frequency sonar signals on alewife (Alosa pseudoharengus). Alewife was selected because of its status as a Species of Concern. Additionally, alewife has an expanded hearing range compared to most fish species and is able to detect mid-frequency sonar. Experimental trials exposed fish to frequency modulated and continuous wave tones (2.5 – 5 kilohertz) with a received peak level of 195 decibels referenced to one micro-Pascal over a two minute time period. The goals of the study were to assess physiological injury through gross examination and to observe behavior using video analysis. There was no mortality associated with the sound exposure in this test. Examination of organs and tissues did not reveal differences between control and exposed groups. Clear behavioral reactions (increased swimming speed and irregular swimming behavior) to sound signals were observed. As each exposure trial progressed, behavioral habituation to sound signals was evident. This study helps to fill a data gap addressing the effects of high intensity non-impulsive sound sources, such as sonar, on fish. The outcomes of this study, no effect to tissues and behavioral habituation, lessen concerns that high intensity mid-frequency sonar signals could have sustained effects on fishes.