Marine mammal strandings associated with specific mid-frequency active sonar (MFAS) systems have driven much of the awareness, research, and regulatory attention to the effects of noise on these taxa. However, controlled measurements of cetacean responses to known exposures of such sounds have been unavailable. Within the Southern California Behavioral Response Study (SOCAL-BRS), we conducted 79 discrete controlled exposure experiments (CEEs) involving > 100 individual marine mammals tagged with high-resolution acoustic and movement sensors exposed to either experimental sources simulating MFAS sonar or full-scale Navy sonars. Operational Navy systems included hull-mounted SQS-53C MFAS from surface ships and AN/AQS-22 helicopter-dipping sonars. Subject species that are commonly exposed to these sonars off California were: Cuvier’s beaked whale (Ziphius cavirostris), blue whale (Balaenoptera musculus), fin whale (Balaenoptera physalus), and Risso’s dolphin (Grampus griseus). Sources were carefully controlled during CEEs and positioned at ranges of 1 to >50 km from subjects depending on conditions using in situ propagation modeling to meet experimental objectives. Incidental MFAS exposures were also evaluated based on calibrated tag measurements and information available for nearby sound sources (e.g., position, source level). Response type and probability differed between species, with beaked whales being the most sensitive, and depended on contextual variables including animal behavioral state, prey distribution, and source-animal range. Results from the largest, loudest sources (53Cs) at farther ranges (tens of km) suggest categorically different and diminished behavioral responses than those documented for similar received levels (100-160 dB re 1µPa) in the same species using simulated MFAS sources at lower source levels and closer ranges (few km). These results have substantial implications for both the regulatory evaluation of MFAS impacts in sonar use areas and our understanding of the contextual nature of marine mammal behavioral response generally, notably the interaction of received level and spatial relationships (range) between source and receiver.
Southall, B., J. Calambokidis, S. DeRuiter, A. Allen, E. Hazen, A. Stimpert, D. Cade, A. Szesciorka, A. Friedlaender, J. Goldbogen, D. Moretti, G. Gailey. 2017. Controlled exposure experiments with full-scale military mid-frequency sonars in four cetacean species. Abstract (Proceedings) 22nd Biennial on the Biology of Marine Mammals, Halifax, Nova Scotia, October 22-27, 2017.