Analysis of frequency structure of sperm whale clicks as a function of dive depth and animal orientation

Abstract

During overnight tracking of a pod of sperm whales in the Gulf of Mexico in July 2000, the NOAA ship GORDON GUNTER recorded their characteristic ‘‘click’’ sounds on a five-element towed hydrophone array. Multiple reflections from the surface and ocean bottom were also recorded. Analysis of the arrival times and bearings of the reflections allowed the computation of three dimensional dive profiles for several animals. By assuming the orientation of the animal was aligned with its velocity, the relative orientation of the animals relative to the array could also be estimated. A visual examination of the frequency content of the received clicks versus dive time suggested that the double resonances in the 1.2 and 2.2 kHz band increased 20%–30% during depth changes of 1000 m. In this presentation the possible relationship between click structure and whale depth and orientation is rigorously analyzed, and the observed relationships are compared with predictions from various sound production and resonator models, in an attempt to gain insight into the sound production mechanism. [Work supported by Minerals Management Service, National Marine Fisheries Service, and ONR.]