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First published online June 13, 2008
Journal of Experimental Biology 211, 2079-2086 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.015081

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The responses of Atlantic cod (Gadus morhua L.) to ultrasound-emitting predators: stress, behavioural changes or debilitation?

Henriette B. Schack^1,*, Hans Malte¹ and Peter T. Madsen^1,2

¹ Zoophysiology, Department of Biological Sciences, University of Aarhus, Bldn. 1131, 8000 Aarhus C, Denmark
² Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA

^* Author for correspondence (e-mail: henriette{at}post.au.dk)

Accepted 16 April 2008

A previous study has reported that Atlantic cod can be conditioned to detect ultrasonic sound pulses of high intensity. This capability has been proposed as a mean for detection and avoidance of echolocating toothed whales that emit intense ultrasonic clicks. In this study, we use acoustic playbacks to test the hypotheses that unconditioned cod can detect and respond to intense ultrasound from toothed whales and from echosounders. Intense ultrasound exposure of 210 dB re. 1µPa (pp) did not cause a short-term stress response in the form of bradycardia in unconditioned cod. Free-swimming cod exposed to ultrasonic clicks and echosounder pulses with received levels of more than 204 dB re. 1 µPa (pp) did not elicit flight responses as seen in ultrasound detecting Alosinae. Furthermore, we tested the debilitating effects of high intensity ultrasound on swimming cod with no detected changes in swimming ability when exposed to more than 213 dB re. 1 µPa (pp). It is concluded that intense ultrasound exposure induces neither an antipredator nor a stress response in Atlantic cod, and that echosounder pulses and biosonar clicks therefore most probably play no ecophysiological role in wild cod populations.