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First published online June 6, 2005
Journal of Experimental Biology 208, 2319-2332 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01624

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Cuvier's beaked whale (Ziphius cavirostris) head tissues: physical properties and CT imaging

Melissa S. Soldevilla^1,*, Megan F. McKenna², Sean M. Wiggins¹, Robert E. Shadwick¹, Ted W. Cranford² and John A. Hildebrand¹

¹ Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0205, USA
² San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, USA

^* Author for correspondence (e-mail: mhock{at}ucsd.edu)

Accepted 29 March 2005

Tissue physical properties from a Cuvier's beaked whale (Ziphius cavirostris) neonate head are reported and compared with computed tomography (CT) X-ray imaging. Physical properties measured include longitudinal sound velocity, density, elastic modulus and hysteresis. Tissues were classified by type as follows: mandibular acoustic fat, mandibular blubber, forehead acoustic fat (melon), forehead blubber, muscle and connective tissue. Results show that each class of tissues has unique, co-varying physical properties. The mandibular acoustic fats had minimal values for sound speed (1350±10.6 m s^–1) and mass density (890±23 kg m^–3). These values increased through mandibular blubber (1376±13 m s^–1, 919±13 kg m^–3), melon (1382±23 m s^–1, 937±17 kg m^–3), forehead blubber (1401±7.8 m s^–1, 935±25 kg m^–3) and muscle (1517±46.8 m s^–1, 993±58 kg m^–3). Connective tissue had the greatest mean sound speed and density (1628±48.7 m s^–1, 1087±41 kg m^–3). The melon formed a low-density, low-sound-speed core, supporting its function as a sound focusing organ. Hounsfield unit (HU) values from CT X-ray imaging are correlated with density and sound speed values, allowing HU values to be used to predict these physical properties. Blubber and connective tissues have a higher elastic modulus than acoustic fats and melon, suggesting more collagen structure in blubber and connective tissues. Blubber tissue elastic modulus is nonlinear with varying stress, becoming more incompressible as stress is increased. These data provide important physical properties required to construct models of the sound generation and reception mechanisms in Ziphius cavirostris heads, as well as models of their interaction with anthropogenic sound.

Key words: Cuvier's beaked whale, Ziphius cavirostris, physical property, sound speed, density, Hounsfield unit, elastic modulus