Abstract
At present, there are no direct measures of hearing for any baleen whale (Mysticeti). The most viable alternative to in vivo approaches to simulate the audiogram is through modeling outer, middle, and inner ear functions based on the anatomy and material properties of each component. This paper describes a finite element model of the middle ear for the humpback whale (Megaptera novaeangliae) to calculate the middle ear transfer function (METF) to determine acoustic energy transmission to the cochlea. The model was developed based on high resolution computed tomography imaging and direct anatomical measurements of the middle ear components for this mysticete species. Mechanical properties for the middle ear tissues were determined from experimental measurements and published values. The METF for the humpback whale predicted a better frequency range between approximately 15 Hz and 3 kHz or between 200 Hz and 9 kHz based on two potential stimulation locations. Experimental measures of the ossicular chain, tympanic membrane, and tympanic bone velocities showed frequency response characteristics consistent with the model. The predicted best sensitivity hearing ranges match well with known vocalizations of this species.
Highlights
Little is known about the impact of anthropogenic noise on baleen whales (Cetacea, suborder Mysticeti)
We modeled the middle ear of the minke whale (Balaenoptera acutorostrata) (Tubelli et al, 2012) computationally using the finite element (FE) method, where geometries of varying complexity are broken up into elements and solved for numerically
We can test the validity of the humpback whale middle ear transfer function (METF) by considering the resultant velocity at the stapes footplate at estimated hearing thresholds compared to those measured in terrestrial mammals
Summary
Little is known about the impact of anthropogenic noise on baleen whales (Cetacea, suborder Mysticeti). The bottlenose dolphin (Tursiops truncatus) has a total hearing range based on audiometric data of approximately 100 Hz to 160 kHz, while their whistles are typically between 1 kHz to 24 kHz and clicks between 30 kHz and 60 kHz (see Wartzok and Ketten, 1999). It is usual for hearing ranges to include vocalization frequencies related to predation and many abiotic signals in addition to the frequencies of conspecific vocalizations (Ketten, 2002).
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