Source level and calling depth distributions of migrating bowhead whale calls in the shallow Beaufort Sea

Aaron M Thode; Susanna B Blackwell; Kerri D Seger; Alex S Conrad; Katherine H Kim; A Michael Macrander

doi:10.1121/1.4968853

Source level and calling depth distributions of migrating bowhead whale calls in the shallow Beaufort Sea

J Acoust Soc Am. 2016 Dec;140(6):4288. doi: 10.1121/1.4968853.

Authors

Aaron M Thode¹, Susanna B Blackwell², Kerri D Seger³, Alex S Conrad², Katherine H Kim², A Michael Macrander⁴

Affiliations

¹ Marine Physical Laboratory, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093-0238, USA.
² Greeneridge Sciences, Incorporated, 90 Arnold Place, Suite D, Santa Barbara, California 93117, USA.
³ University of New Hampshire, 24 Colovos Road, Durham, New Hampshire 03824, USA.
⁴ Shell Exploration and Production Company, 3601 C Street, Anchorage, Alaska 99503, USA.

PMID: 28040014
DOI: 10.1121/1.4968853

Abstract

Automated and manual acoustic localizations of migrating bowhead whales were used to estimate source level and calling depth distributions of their frequency-modulated-modulated calls over seven years between 2008 and 2014. Whale positions were initially triangulated using directional autonomous seafloor acoustic recorders, deployed between 25 and 55 m water depth near Kaktovik, Alaska, during the fall westward migration. Calling depths were estimated by minimizing the "discrepancy" between source level estimates from at least three recorders detecting the same call. Applying a detailed waveguide propagation model to the data yielded broadband source levels of 161 ± 9 dB re 1 μPa² s at 1 m (SEL) for calls received between 20 and 170 Hz. Applying a simpler 15 log₁₀(R) power-law propagation model yielded SEL source levels of 158 ± 10 dB. The most probable calling depths lay between 22 and 30 m: optimal depths for long-range acoustic signal transmission in this particular environment.