title: Fin whale sound reception mechanisms: skull vibration enables low-frequency hearing.
abstract: Hearing mechanisms in baleen whales (Mysticeti) are essentially unknown but their vocalization frequencies overlap with anthropogenic sound sources. Synthetic audiograms were generated for a fin whale by applying finite element modeling tools to X-ray computed tomography (CT) scans. We CT scanned the head of a small fin whale (Balaenoptera physalus) in a scanner designed for solid-fuel rocket motors. Our computer (finite element) modeling toolkit allowed us to visualize what occurs when sounds interact with the anatomic geometry of the whale's head. Simulations reveal two mechanisms that excite both bony ear complexes, (1) the skull-vibration enabled bone conduction mechanism and (2) a pressure mechanism transmitted through soft tissues. Bone conduction is the predominant mechanism. The mass density of the bony ear complexes and their firmly embedded attachments to the skull are universal across the Mysticeti, suggesting that sound reception mechanisms are similar in all baleen whales. Interactions between incident sound waves and the skull cause deformations that induce motion in each bony ear complex, resulting in best hearing sensitivity for low-frequency sounds. This predominant low-frequency sensitivity has significant implications for assessing mysticete exposure levels to anthropogenic sounds. The din of man-made ocean noise has increased steadily over the past half century. Our results provide valuable data for U.S. regulatory agencies and concerned large-scale industrial users of the ocean environment. This study transforms our understanding of baleen whale hearing and provides a means to predict auditory sensitivity across a broad spectrum of sound frequencies.
authors: San Diego State University, Department of Biology, San Diego, California, United States of America, and Quantitative Morphology Consulting, Inc., San Diego, California, United States of America.
authors: Ted W
authors: TW
authors: Cranford
authors: University of California San Diego, Department of Structural Engineering, La Jolla, California, United States of America.
authors: Petr
authors: P
authors: Krysl
mesh_terms: D000818:Animals; D050617:Fin Whale / Q000502:physiology*; D006309:Hearing / Q000502:physiology*; D006320:Hearing Tests; D008954:Models, Biological; D012886:Skull / Q000502:physiology*; D013016:Sound; D014732:Vibration; D014828:Vocalization, Animal / Q000502:physiology
references: Science. 1980 Feb 8;207(4431):663-5
references: 17749328
references: Anat Rec (Hoboken). 2008 Apr;291(4):353-78
references: 18228579
references: Anat Rec (Hoboken). 2012 Jun;295(6):991-8
references: 22488847
references: Anat Rec (Hoboken). 2007 Jun;290(6):716-33
references: 17516434
references: PLoS One. 2012;7(8):e42591
references: 22912710
references: J Acoust Soc Am. 1968 Oct;44(4):965-7
references: 5683663
references: Proc Natl Acad Sci U S A. 2002 Oct 1;99(20):13206-10
references: 12239353
references: PLoS One. 2010 Aug 04;5(8):e11927
references: 20694149
references: J Acoust Soc Am. 2006 Oct;120(4):2328-39
references: 17069328
references: Adv Exp Med Biol. 2012;730:69-72
references: 22278452
references: PLoS One. 2011;6(6):e21311
references: 21731700
references: Adv Exp Med Biol. 2012;730:105-7
references: 22278460
references: J Acoust Soc Am. 1999 Aug;106(2):1134-41
references: 10462816
references: Mar Biol. 2013;160(1):47-57
references: 24391281
references: Am Mineral. 2014 Apr;99(4):645-653
references: 25484370
references: Acta Otolaryngol. 1951 Jun;38(3):262-73
references: 14856657
references: Adv Anat Embryol Cell Biol. 1978;55(5):3-70
references: 735912
references: Science. 2014 Jan 10;343(6167):128
references: 24408410
references: J Acoust Soc Am. 2012 Nov;132(5):3263-72
references: 23145610
references: Bioinspir Biomim. 2008 Mar;3:016001
references: 18364560
references: J Acoust Soc Am. 2009 Feb;125(2):1230-9
references: 19206896