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First published online September 11, 2009
Journal of Experimental Biology 212, 3100-3107 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.030825

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Acoustic behaviour of echolocating porpoises during prey capture

Stacy L. DeRuiter^1,2,*, Alexander Bahr³, Marie-Anne Blanchet⁴, Sabina Fobian Hansen⁵, Jakob Højer Kristensen⁵, Peter T. Madsen^6,2, Peter L. Tyack² and Magnus Wahlberg^5,7

¹ IFREMER, Service Acoustique et Sismique, B.P. 70, 29280 Plouzané, France
² Biology Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
³ Massachusetts Institute of Technology, Center for Ocean Engineering, 32 Vassar Street, Cambridge, MA 02139, USA
⁴ Idrettsvein 40B, 9009 Tromsø, Norway
⁵ Fjord and Baelt, Margrethes Plads 1, DK-5300 Kerteminde, Denmark
⁶ Department of Biological Sciences, Zoophysiology, Aarhus University, C.F. Møllers Allé, Building 1131, DK-8000 Aarhus C, Denmark
⁷ Marine Biological Laboratory, University of Southern Denmark, Hindsholmsvej 10, 5300 Kerteminde, Denmark

^* Author for correspondence (stacy_deruiter{at}yahoo.com)

Accepted 30 June 2009

Porpoise echolocation has been studied previously, mainly in target detection experiments using stationed animals and steel sphere targets, but little is known about the acoustic behaviour of free-swimming porpoises echolocating for prey. Here, we used small onboard sound and orientation recording tags to study the echolocation behaviour of free-swimming trained porpoises as they caught dead, freely drifting fish. We analysed porpoise echolocation behaviour leading up to and following prey capture events, including variability in echolocation in response to vision restriction, prey species, and individual porpoise tested. The porpoises produced echolocation clicks as they searched for the fish, followed by fast-repetition-rate clicks (echolocation buzzes) when acquiring prey. During buzzes, which usually began when porpoises were about 1–2 body lengths from prey, tag-recorded click levels decreased by about 10 dB, click rates increased to over 300 clicks per second, and variability in body orientation (roll) increased. Buzzes generally continued beyond the first contact with the fish, and often extended until or after the end of prey handling. This unexplained continuation of buzzes after prey capture raises questions about the function of buzzes, suggesting that in addition to providing detailed information on target location during the capture, they may serve additional purposes such as the relocation of potentially escaping prey. We conclude that porpoises display the same overall acoustic prey capture behaviour seen in larger toothed whales in the wild, albeit at a faster pace, clicking slowly during search and approach phases and buzzing during prey capture.

Key words: echolocation, porpoise, foraging, buzz, biosonar, Phocoena

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