Foraging Behavior and Disruption in Blue, Fin, and Humpback Whales in Relation to Sonar Exposure: The Challenges of Generalizing Responsiveness in Species with High Individual Variability

Behavioral response studies (BRSs) are an important approach for quantifying responses of marine mammals to naval sonar exposure. Controlled exposure experiments (CEEs) are BRSs based on a formal experimental design. Impact assessment often requires prediction of the likelihood that an individual of any species present in an area will respond to a given dose of sonar. Empirical data exist for only a few species, and species are often grouped to enable estimation of responsiveness for unstudied species. In this study, data for three taxonomically close species were combined to quantitatively determine whether they could be grouped in terms of responsiveness. We focused on foraging responses of blue (Balaenoptera musculus), fin (Balaenoptera physalus), and humpback (Megaptera novaeangliae) whales in relation to sonar exposure. These species are lunge filter feeders, and the number of lunges within each phase of a CEE was used to test for changes in foraging in response to exposure. Humpback whales, which were exposed to the highest sound levels, were found to be more responsive during and after sonar exposure when compared with blue and fin whales. The lunge rates of blue and fin whales throughout the sonar exposures remained similar to baseline and no sonar control levels. The greatest challenge is the ability to generalize responsiveness in species for which responses at the individual level are probably rare and subtle. Moreover, the interpretation of these species' similarities and individual differences in responsiveness is problematic given the contextual differences between each CEE. As in previous studies, our results reinforce the need for BRSs to incorporate environmental data collection that is relevant to the behavioral state of study animals.