Abstract

The effects of three sonar sound types (peak frequency ca. 25 kHz with high-frequency side bands at 71 and 121 kHz) on the behavior of a harbor porpoise (Phocoena phocoena) were quantified in a quiet pool. Sequences (with different pulse intervals, resulting in different duty cycles) of 50-ms frequency modulated (FM) signals, 600-ms continuous waves (CW), and 900-ms combinations of FM and CW signals (Combo) were transmitted at four average received broadband sound pressure levels (SPLsav.re.) to determine the dose-response relationship. Effects ranged from just no change in the harbor porpoise’s respiration rate to increases of 53% (FM), 38% (CW), and 63% (Combo). The animal’s agitation was evidenced by increased jumps, and his response increased with SPL. SPLsav.re. causing responses were 125 to 148 dB re 1 μPa (FM) and 118 to 153 dB re 1 μPa (CW and Combo). At the same SPLsav.re., the greatest response was to the Combo signal (at the duty cycles used in this study). At sea, harbor porpoise response distances will vary with context such as, for example, social situation, sound propagation, and background noise levels.