Northern Elephant Seals Adjust Gliding and Stroking Patterns with Changes in Buoyancy: Validation of At-Sea Metrics of Body Density

• Main Authors: Aoki, Kagari, Watanabe, Yuuki Y., Crocker, Daniel E., Robinson, Patrick W., Biuw, Martin, Costa, Daniel P., Miyazaki, Nobuyuki, Fedak, Mike A., Miller, Patrick J.O.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Journal of Experimental Biology 2011
• Subjects: acceleration; body condition; body density; buoyancy; drag; elephant seal; Elephant Seal; Elephant Seals
• Online Access: http://hdl.handle.net/10211.3/118192

Published by and copyright of The Company of Biologists. The definitive version of this article is available at: http://jeb.biologists.org/content/214/17/2973.full.pdf+html?with-ds=yes Many diving animals undergo substantial changes in their body density that are the result of changes in lipid content over their annual fasting cycle. Because the size of the lipid stores reflects an integration of foraging effort (energy expenditure) and foraging success (energy assimilation), measuring body density is a good way to track net resource acquisition of free-ranging animals while at sea. Here, we experimentally altered the body density and mass of three free-ranging elephant seals by remotely detaching weights and floats while monitoring their swimming speed, depth and three-axis acceleration with a high-resolution data logger. Cross-validation of three methods for estimating body density from hydrodynamic gliding performance of freely diving animals showed strong positive correlation with body density estimates obtained from isotope dilution body composition analysis over density ranges of 1015 to 1060kg m???3. All three hydrodynamic models were within 1% of, but slightly greater than, body density measurements determined by isotope dilution, and therefore have the potential to track changes in body condition of a wide range of freely diving animals. Gliding during ascent and descent clearly increased and stroke rate decreased when buoyancy manipulations aided the direction of vertical transit, but ascent and descent speed were largely unchanged. The seals adjusted stroking intensity to maintain swim speed within a narrow range, despite changes in buoyancy. During active swimming, all three seals increased the amplitude of lateral body accelerations and two of the seals altered stroke frequency in response to the need to produce thrust required to overcome combined drag and buoyancy forces. This work was funded by the program bio-logging Science of the University of Tokyo (UTBLS), Grant-in Aids for Science Research from the Japan Society for the Promotion of Science (21681002), the National Environment Research Council (NERC NE/c00311X/1), the National Ocean Partnership Program (N00014-02-1-1012), the Office of Naval Research (N00014-00-1-0880 & N00014-03-1-0651), and the Moore, Packard and Sloan Foundations.