At the ongoing 22nd Biennial Conference on the Biology of Marine Mammals. Halifax, Nova Scotia, Canada, SEA Senior Scientist Dr. Brandon Southall presented results from the first-ever experimental study of the potential effects of high-power military sonar. This study involved measurements of behavioral responses of several marine mammal species exposed in controlled conditions to navy ships operating the highest-power, mid-frequency sonar systems. These kinds of sonar systems have been involved in a number of previous marine mammal stranding events. Navies around the world, most notably the U.S. Navy, have been supporting extensive research to try and understand what the potential risks from these systems may be and how they might be mitigated. Subject species included beaked whales, blue whales, fin whales, and Risso’s dolphins in studies spanning five years off of southern California.
Through the support of and logistical cooperation with the U.S. Navy (primarily the Living Marine Research Program along with the Office of Naval Research Marine Mammal Program), SEA scientists as well as research partners from many academic, private, and government research organizations worked together to carefully expose animals to realistic scenarios with operational, full-scale sonar systems using controlled experimental methods. The results indicated behavioral responses (changes in diving and feeding behavior) within some individuals, but that compared with the probability of responses for less powerful systems operated closer to animals the relative probability of response for the same sound levels was substantially reduced. This gives us some insight into the increasingly clear picture that contextual aspects of sound exposure, such as distance, relative motion, and familiarity of the noise animals are exposed to, may be as or even more important in terms of predicting response probability than simply how loud the sound is. These studies are helping us understand many basic aspects of behavior and context-dependencies, as well as applied questions about response probability for operational sources in the ocean.