Sperm whale clicks: Directionality and source level revisited

In sperm whales (Physeter catodon L. 1758) the nose is vastly hypertrophied , accounting for about one-third of the length or weight of an adult male. Norris and Harvey [in Animal Orientation and Navigation, NASA SP-262 (1972) , pp. 397-417] ascribed a sound-generating function to this organ complex. A sound generator weighing upward of 10 tons and with a cross-section of 1 m is expected to generate high-intensity, directional sounds. This predicti on from the Norris and Harvey theory is not supported by published data for sperm whale clicks (source levels of 180 dB re 1 mu Pa and little, if any, directionality). Either the theory is not borne out or the data is not rep resentative for the capabilities of the sound-generating mechanism. To incr ease the amount of relevant data, a five-hydrophone array, suspended from t hree platforms separated by 1 km and linked by radio, was deployed at the s lope of the continental shelf off Andenes, Norway, in the summers of 1997 a nd 1998. With this system, source levels up to 223 dB re 1 mu Pa peRMS were recorded. Also, source level differences of 35 dB for the same click at di fferent directions were seen, which are interpreted as evidence for high di rectionality. This implicates sonar as a possible function of the clicks. T hus, previously published properties of sperm whale clicks underestimate th e capabilities of the sound generator and therefore cannot falsify the Norr is and Harvey theory. (C) 2000 Acoustical Society of America. [S0001-4966(0 0)03301-4].