Behavioral Response Studies in southern California (SOCAL-BRS): Progress to date and evolution to realistic exposure scenarios

Speaker: Brandon Southall and Jeremy Goldbogen  (University of California and Stanford University)

Abstract

SOCAL-BRS is a multi-team collaboration designed to increase understanding of marine mammal behavior and provide a more robust scientific basis for estimating risk and minimizing effects of active, mid-frequency military sonar systems. The research team includes interdisciplinary expertise in marine mammal biology, behavior, and communication, as well as underwater acoustics, engineering, and biostatistics. Four field seasons were conducted involving visual observations, passive acoustic monitoring, animal-attached acoustic and movement tags, photo ID, biopsy, and controlled sound exposure methods on over 20 cetacean species in biologically important areas throughout the southern California Bight. Over 125 individuals of nine species were tagged with six tag types, including several [Baird’s beaked whale (Berardius bairdii), Risso’s dolphin (Grampus griseus)] that had not been previously studied using such monitoring tools. Over 70 controlled sound exposure experiments were conducted using specific protocols and protective measures to ensure animals were not harmed. Several sound types, including both simulated and in 2013 actual military sonar, were projected through a deployed sound source from a research vessel and changes in vocal, diving, and horizontal movement behavior were measured. For baleen whales, active acoustic measurements of prey fields for foraging animals were integrated into statistical analyses of potential responses to sound. Results demonstrate the importance of measuring context-relevant environmental parameters in interpreting response; the inclusion of prey metrics explains four times more variance in dive metrics than playback data alone. Results to date indicate that Cuvier’s beaked whales (Ziphius cavirostris) react most strongly to simulated sonar exposures with clear changes in vocal and diving behavior indicating avoidance responses at low received sound levels. Blue whale (Balaenoptera musculus) responses are more variable and depend on complex interactions of exposure conditions and individual behavioral state. Ongoing efforts include expanding sample sizes in other species using simulated sounds and the novel experimental use of operational Navy mid-frequency sonar systems.