Hearing sensitivities and sound pathways in odontocetes

Abstract

Sound is of primordial importance for marine mammals and the impact of anthropogenic noise on their life history is still largely unknown. Understanding how odontocetes or toothed whales have evolved a highly specialized hearing system has also been the focus of intensive research both in the laboratory as well as in the field. The use of auditory evoked potentials to study hearing in whales and dolphins has allowed scientists to obtain rapidly hearing measurements in species that were not easily accessible. This dissertation presents an overview of a travel system used to rapidly and non-invasively measure the hearing of odontocetes. In addition, this work presents the basic hearing measurements or audiograms of two new species of odontocetes; the long-finned pilot whale (Globicephala melas) and the Blainville's beaked whale (Mesoplodon densirostris). Hearing pathway differences in two species of odontocetes, the atlantic bottlenose dolphin (Tursiops truncatus) and the false killer whale (Pseudorca crassidens) were also collected and potential interspecies variations were discussed. The last chapter presents the results of an experiment investigating echolocation disruption in the false killer whale using an acoustic pinger to mitigate by catch in Hawaiian fisheries. This dissertation combines non only data on the basic hearing of new species and a new perspective of the complex hearing mechanisms and hearing pathways variations across odontocetes, but it also provides baseline data to address important conservation issues such as the effects of noise on marine mammals as well as the feasibility of using acoustic deterrents to mitigate interactions with fisheries. Understanding how different species of odontocetes evolve, use and react to sound is important to build successful conservation strategies that will both protect animal species as well as accommodate human activities when it is possible.