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Sperm whale sound production studied with ultrasound time/depth-recording tags

P. T. Madsen^1,*, R. Payne², N. U. Kristiansen¹, M. Wahlberg¹, I. Kerr² and B. Møhl¹

¹ Department of Zoophysiology, Institute of Biological Sciences, University of Aarhus, Building 131, 8000 Aarhus C, Denmark
² The Ocean Alliance/The Whale Conservation Institute, 191 Weston Road, Lincoln, MA 01775, USA

View larger version (34K): [in a new window]   Fig. 1. Schematic view of the head of a 10 m long sperm whale (Physeter macrocephalus) showing placement of the tag. B, brain; B1, blow hole; Di, distal air sac; Fr, frontal air sac; Ju, junk; Ln, left naris; Ma, mandible; Mo, monkey lips/museau de singe; MT, muscle/tendon layer; Ro, rostrum; Rn, right naris; So, spermaceti organ; T, tag. Spermaceti oil is contained in the spermaceti organ and in the spermaceti bodies of the junk. The muscle/tendon layer covers the entire dorso-lateral part of the spermaceti organ and inserts into the connective tissue around and in front of the monkey lips. Arrows indicate the sound path according to the modified (by Møhl, 2001) theory of Norris and Harvey (1972): it is proposed that air forced from the right naris through the monkey lips generates the sound pulse. The majority of the sound energy is due to the geometry of the lips and the reflective properties of the distal air sac, directed backwards into the spermaceti organ. When it reaches the frontal air sac, the sound pulse is reflected into the junk complex and directed into the water in front of the whale. The multi-pulse structure of sperm whale clicks appears to be generated by partial interception by the distal air sac of the forward-propagating pulse, leading to another round trip during which another fraction of the sound energy is intercepted by the distal air sac and so on.

View larger version (165K): [in a new window]   Fig. 2. Attachment of the tag by means of a pole and suction cup. Tagger, J. Jones; photograph by C. Johnson/Ocean Alliance.

View larger version (18K): [in a new window]   Fig. 3. Dive profile of a tagged sperm whale. Circles indicates the production of coda clicks and triangles the production of usual clicks. Note that the whale stops clicking during most of the ascent. Water depth is 940m. Total number of coda clicks, 54. Total number of usual clicks, 1804. Inset, reduction in air volume as a function of depth (PV=C, where P is pressure, V is volume and C is a constant). Note the logarithmic scale on the ordinate.

View larger version (25K): [in a new window]   Fig. 4. Inter-click interval (open circles) and dive depth as a function of click number during each of the 1804 usual clicks produced during the dive profiled in Fig. 3.

View larger version (25K): [in a new window]   Fig. 5. Recorded sound level (open circles) and dive depth as a function of click number during the dive profiled in Fig. 3.

View larger version (12K): [in a new window]   Fig. 6. Waveforms of usual and coda clicks. (A) Waveform of a usual click recorded at depth of 630m. The recorded level of the initial pulse (p0) is 185 dB re. 1 µPa (peak to peak). (B) Waveform of a coda click recorded at a depth at 70 m. The recorded level of the p0 pulse is 165 dB re. 1 µPa (peak to peak). Note that the inter-pulse interval is the same in the usual click and the coda click (3.4ms). Pulses labelled as in Møhl (2001).

View larger version (20K): [in a new window]   Fig. 7. Centroid frequency and recorded sound level. Centroid frequency (the frequency that divides the spectrum in two parts of equal energy) as a function of recorded level (1 dB bins). The solid line is the linear regression curve fitted to the data (r=0.70, P<0.001, N=1804). The increase in centroid frequency is 1 octave per 25 dB increase in recorded level.