Abstract:

Aerial (100 Hz to 28 kHz) and underwater (75 Hz to 59.8 kHz) sound detection thresholds were determined for a female northern elephant seal (Mirounga angustirostris) using behavioral psychophysical techniques. The resulting underwater audiogram shows a typical phocid pattern, with an upper frequency limit of about 59 kHz and relatively flat sensitivity from about 200 Hz to 30 kHz. In air, the elephant seal is 10--30 dB less sensitive than other phocid species tested. Underwater sound pressure thresholds averaged about 15 dB lower than aerial pressure thresholds. The degree of adaptation to underwater hearing in pinnipeds seems to follow phylogenetic trends; however, a high degree of aquatic specialization occurs in the northern elephant seal. Because the elephant seal is apparently nonvocal underwater, the most likely explanation for this high degree of aquatic hearing specialization lies in its ability to dive regularly to depths of 500--700 m. Although the elephant seal has poor aerial hearing relative to other pinnipeds, it has compensated for this deficiency by emitting very loud aerial vocalizations associated with seismic and visual signals to facilitate effective aerial communication. [Work supported by ONR.]