Dall’s porpoise (Phocoenoides dalli) echolocation click spectral structure.

Abstract

Dall’s porpoise (Phocoenoides dalli) echolocation clicks have not been widely recorded. Concurrent with visual observations, acoustic recordings of free-ranging Dall’s porpoise were made offshore of southern California using a towed hydrophone array with two elements of 250 kHz bandwidth. We examined 6035 clicks from 12 sessions totaling more than two hours over the course of seven days. The Dall’s porpoise echolocations recorded were short (48–804 μs), narrow band (2–10 kHz [−3dB]) clicks with most peak frequencies between 117 and 141 kHz, but some as high as 198 kHz. Many clicks contained a multipulse temporal structure, resulting in stereotyped spectral peaks and notches. Two distinctive click types with different spectral banding patterns and peak frequencies (122.8 and 135.8 kHz) were observed. Spectral banding patterns have been used as a species identifier for Risso’s dolphins and Pacific white-sided dolphins. These two dolphins and Dall’s porpoise have similar head morphologies, which may play a role in producing clicks with spectral peaks and notches. This study shows that Dall’s porpoise produce multiple click types, which may provide a tool for population classification, and that their clicks contain spectral banding patterns, which may provide insight into the mechanism by which such clicks are produced.