Prediction of a mysticete audiogram via finite element analysis of the middle ear.

The impact of anthropogenic sound on marine mammals is difficult to assess, especially for species without available audiograms. There are currently no audiograms for any species of mysticete because of their size and, in many cases, their endangerment status. Consequently, insight into the hearing range of all mysticete species comes from indirect sources such as vocalization recordings. In contrast to mysticetes, several odontocete species have published audiograms. Both the middle ear and the cochlea play an important role in shaping the audiogram of any mammal. The transfer function of the middle ear shapes the low-frequency portions of an audiogram, whereas the high-frequency portion of the audiogram is shaped by the frequency place map of the cochlea (Rosowski 1994). Biophysical models of the cetacean middle ear can be developed using finite element (FE) techniques. FE modeling has been successfully used to provide an understanding of how several terrestrial mammalian middle ear systems work. The advantage to using FE models is that they directly incorporate the geometry and material properties of the structures of interest. For this study, the middle ear of a mysticete species, Balaenoptera acutorostrata (minke whale), was modeled using FE methods. The same methods were used to develop a model for the Tursiops truncatus (bottlenose dolphin) middle ear, a control species that has a behaviorally derived audiogram to verify the modeling approach.