FIRST DESCRIPTION OF WHISTLES OF PACIFIC FRASER'S DOLPHINS LAGENODELPHIS HOSEI

ABSTRACT

Acoustic recordings were made in the presence of four single-species schools of Fraser's Dolphin Lagenodelphis hosei during combined acoustic and visual shipboard line-transect cetacean abundance surveys. Recordings were made using a towed hydrophone array and sonobuoys. Echolocation clicks were detected during only one recording session and no burst pulses were detected. Whistles were present in all four recording sessions. Fourteen variables were measured from the fundamental frequencies of 60 whistles. The whistles were generally simple, with few inflection points or steps. Whistles ranged from 6.6 kHz to 23.5 kHz, with durations ranging from 0.06 to 0.93 sec. Whistle characteristics closely match those reported for L. hosei recorded in the Gulf of Mexico (Leatherwood et al. 1993) and the Caribbean (Watkins et al. 1994), although, in general, the Pacific dolphins were less vocally active than the Caribbean dolphins described by Watkins et al. (1994). This difference may be related to the orientation of the hydrophone array relative to the dolphins. It may also be due to behaviour, as the Caribbean dolphins were engaged in feeding activities and the Pacific dolphins were fast travelling to evade the approaching vessel.

Keywords:

• whistles
• Lagenodelphis hosei
• tropical Pacific