The auditory system of the minke whale (Balaenoptera acutorostrata) : a potential fatty sound reception pathway in a mysticete cetacean

• Main Author: Yamato, Maya
• Format: Thesis
• Language: English
• Published: Massachusetts Institute of Technology and Woods Hole Oceanographic Institution 2012
• Subjects: Minke whale; Hearing; Balaenoptera acutorostrata; baleen whales; minke whale; toothed whales
• Online Access: https://hdl.handle.net/1912/5661

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2012 Despite widespread concerns about the effects of anthropogenic noise on baleen whales (suborder Mysticeti), we lack basic information about their auditory physiology for comprehensive risk assessments. Hearing ranges and sensitivities could be measured if customized equipment and methods were developed based on how baleen whales receive sound. However, sound reception pathways in baleen whales are currently unknown. This thesis presents an integrative approach to understanding hearing in baleen whales through dissections, biomedical imaging, biochemical analyses, and modeling sound propagation through a whale head using the Finite Element Method (FEM). We focused on the minke whale (Balaenoptera acutorostrata) because it is one of the smallest and most abundant mysticete species, reducing logistical difficulties for dissections and experiments. We discovered a large, well-formed fat body extending from the blubber region to the ears and contacting the ossicles. Although odontocetes, or toothed whales, are thought to use specialized “acoustic fats” for sound reception, no such tissues had been described for mysticetes to date. Our study indicates that the basic morphology and biochemical composition of the minke whale “ear fats” are very different from those of odontocete acoustic fats. However, the odontocete and mysticete fatty tissues share some characteristics, such as being conserved even during starvation, containing fewer dietary signals compared to blubber, and having well-defined attachments to the tympano-periotic complex, which houses the middle and inner ears. FE models of the whale head indicated that the ear fats caused a slight increase in the total pressure magnitude by the ears, and this focusing effect could be attributed to the low density and low sound speed of the ear fats in the models. Fatty ...