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First published online June 6, 2005
Journal of Experimental Biology 208, 2459-2466 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01619
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Acoustic characteristics of underwater tail slaps used by Norwegian and Icelandic killer whales (Orcinus orca) to debilitate herring (Clupea harengus)

Malene Simon1,2,*, Magnus Wahlberg3, Fernando Ugarte2 and Lee A. Miller1

1 Institute of Biology, University of Southern Denmark-Odense, Denmark
2 Sea Watch Foundation Cymru, New Quay, Wales, UK
3 Department of Zoophysiology, Institute of Biological Sciences, University of Aarhus, Denmark

* Author for correspondence (e-mail: mjsimon{at}bi.ku.dk)

Accepted 29 March 2005

Norwegian killer whales debilitate prey by slapping their tails into herring schools. These underwater tail slaps produce a thud-like sound. It is unclear whether this sound is caused by cavitation and/or physical contact between herring and whale tail. Also the forces causing debilitation of the fish are not understood. Here we present an acoustic analysis of underwater tail slaps using a multi-channel wide (150 kHz) band recording system. Underwater tail slaps produced by Norwegian killer whales generated sounds consisting of multiple pulses with source levels of 186±5.4 dB (pp) re.1 µPa at 1 m (±1 S.D., N=4). The –3 dB and 97% energy bandwidths were 36.8±22.5 kHz and 130.5±17.5 kHz (±1 S.D., N=13), respectively, with a centre frequency of 46.1±22.3 kHz. The similarities between the acoustic properties of underwater tail slaps recorded from killer whales in Norway, and thud-like sounds recorded from killer whales in Iceland suggest that Norwegian and Icelandic killer whales use similar hunting techniques. The acoustic characteristics of sounds produced by underwater tail slaps were similar to the ones from other cavitation sound sources described in the literature, both in term of temporal and frequency features as well as in source level. We suggest that multiple factors generated by the tail slaps like particle fluctuations, turbulence, pressure changes and physical impact cause debilitation of herring.

Key words: killer whale, Orcinus orca, foraging, prey debilitation, tail slap, cavitation, acoustics


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© The Company of Biologists Ltd 2005