The acoustic behaviour of diving sperm whales observed with a hydrophone array

Abstract Clicks of male sperm whales ( Physeter catodon Linneaus) were recorded off Northern Norway using a hydrophone array. The 3-D diving behaviour in one complete (34 min) and four incomplete (6–36 min) dives was observed using passive acoustic localization. The vertical swim speed was 0.8–1.4 m/s, and the horizontal swim speed was 0.2–2.6 m/s. The maximum dive depth of an individual track ranged from 358 to 1494 m. The bottom depth was 500 to 1600 m and a scattering layer was present at 250 m. Clicks were usually emitted with inter-click intervals (ICI) of 0.5–2 s in blocks of 29–249 clicks, interspaced by pauses of 6–117 s. The length of blocks decreased with depth in a manner predictable from a pneumatic sound generator. Click sequences with shorter inter-click intervals, denoted creaks and believed to indicate feeding events, were located at depths from 278 to 1245 m. This study suggests that sperm whales exploit prey in a large part of the water column below the scattering layer and use an air-driven sound production system.