Sperm whale foraging behavior changes in response to anthropogenic sound
DeRuiter, S, S Isojunno, I Noirot, A Stimpert, W Zimmer, M Leung, C Harris, L Thomas, B Southall, J Calambokidis, P Tyack, and P Miller. 2015. Sperm whale foraging behavior changes in response to anthropogenic sound. Abstract (Proceedings) 21st Biennial Conference on the Biology of Marine Mammals, San Francisco, California, December 14-18, 2015.
Understanding cetacean behavioral reactions to anthropogenic sound is critical for designing appropriate management strategies to predict and mitigate adverse behavioural responses to noise. Foraging behavior is of particular interest, since energetic balance is closely linked to fitness and reproductive success. In order to quantify changes in sperm whale echolocation-based foraging behavior in response to sound, we studied sperm whales equipped with DTAGs, multi-sensor tags that record sound as well as dive depth and movements. Collaborative effort by the MOCHA, 3S, Sirena, SWSS, and SOCAL-BRS projects provided a unique opportunity for coordinated analysis of responses of sperm whales to diverse anthropogenic sounds. Data were collected between 2000-2010 in the North Atlantic, Mediterranean Sea, Gulf of Mexico, and North Pacific, and include experimental exposures of both solitary males and mixed groups to various sounds: 7 to airgun arrays, 7 to naval mid-frequency sonars and similar sounds, and 1 to pseudo-random noise. Tag acoustic records allowed unambiguous classification of foraging behavior states: production of echolocation clicks indicated searching for prey, a buzz (series of very rapid clicks) indicated a prey-capture attempt, and non-foraging periods lacked clicks. We fitted a continuous-time semi-Markov model to the behavior state data. A likelihood-based model-fitting and model-selection framework governed inclusion of parameters allowing for inter-individual differences, as well as effects of acoustic disturbance. Overall, the results allowed us to detect and describe subtle, yet consistent changes in sperm whale foraging behavior in response to acoustic disturbance, with a general trend toward changes likely to reduce foraging efficiency. Examples include longer searches without intervening capture attempts, and longer non-foraging periods. These short-term behavioral responses to acoustic disturbance can be combined with data on the frequency and durations of such disturbances to understand the longer-term effects of noise on a population, and to inform management actions.