Echolocation-based Foraging by Harbor Porpoises and Sperm Whales, Including Effects of Noise and Acoustic Propagation

Stacy L. DeRuiter, Ph.D., 2008
Peter Tyack, Advisor

This thesis provides quantitative descriptions of toothed whale echolocation and foraging behavior, including assessment of the effects of noise on foraging behavior and the potential influence of ocean acoustic propagation conditions on biosonar detection ranges and whale noise exposure. Chapter 2 details the application of a modified version of the Dtag to study harbor porpoise echolocation. Study results indicate how porpoises vary the rate and level of their echolocation clicks during prey capture events and show that, unlike bats, porpoises continue their echolocation buzz after prey capture. Chapters 3-4 emphasize the importance of applying realistic models of ocean acoustic propagation in marine mammal studies. These chapters illustrate that geometric spreading approximations sometimes provide inaccurate predictions of communication/target detection ranges or noise exposure levels, especially if refraction in the water column or multi-path acoustic propagation are significant. Finally, in Chapter 5, I describe two methods for statistical analysis of whale behavior data, a rotation test and a semi-Markov chain model. I use them test for changes in sperm whale foraging behavior in response to airgun noise exposure. Test results indicate that, despite the low-level exposures in the study, some whales altered their foraging behavior in response to airgun exposure.