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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 Simon^1,2,*, 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

View larger version (10K): [in a new window]   Fig. 1. The four-element hydrophone array used to record underwater sounds of Norwegian killer whales.

View larger version (60K): [in a new window]   Fig. 2. Waveform (above) and spectrogram (below) of an underwater tail slap recorded from killer whales in Norwegian waters (recording bandwidth: 150 kHz). The waveform shows the multi-pulsed structure of the sounds produced during underwater tail slaps. This tail slap consisted of 15 single bursts of pulses (numbered in the figure). The vertical lines in the waveform mark the total duration (total) of the tail slap. The arrow points at the pulse shown in Fig. 4. (Spectrogram settings: FFT size 512 pts. Hann window, overlap 75%, sampling frequency 384 kHz.)

View larger version (29K): [in a new window]   Fig. 3. Killer whale underwater tail slap extracted from video recordings (top) and the corresponding sound track (bottom). The letters of the video frames correspond to the times illustrated in the sound track. The clicks before and after the underwater tail slap are killer whale echolocation clicks (arrows).

View larger version (26K): [in a new window]   Fig. 4. (A) Single pulse from a burst of pulses made during an underwater tail slap recorded from killer whales in Norway. The main-pulse is from the tail slap shown in Fig. 2 (arrow). The vertical lines limit the area over which the frequency spectrum in Fig. 4B is calculated. The y-axes denote the received level in Pascal and dB re. 1 µPa at 1 m. The small figure in the top left corner is the waveform of a pulse produced by snapping shrimp, the y-axis denotes dB re. 1 µPa at 1 m (modified after Versluis et al., 2000). (B) Frequency spectrum of the pulse shown in Fig. 4A. The lower line is the background noise sampled before the beginning of the tail slap. Both spectra were calculated with a rectangular window, FFT 128 pts). Noise and signal were measured with exactly the same amplification and filtering, and without any range-dependent compensation.

View larger version (20K): [in a new window]   Fig. 5. Example of multi-pulsed sounds recorded from killer whales in Norwegian (A) and Icelandic (B) waters illustrating the similarity between the two sounds. The sounds recorded from Norwegian killer whales (recorded with a bandwidth of 150 kHz) were filtered with a low-pass filter at 20 kHz to make them comparable to the recordings from Icelandic killer whales (which were recorded with a bandwidth of 20 kHz).

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