Abstract: The effect of three sonar sound types (around 25 kHz) on the behavior of two harbor seals was quantified in a quiet pool. The behavioral response threshold for each sound type was determined by transmitting at three sound pressure levels (SPLs). Sequences were 50-ms frequency modulated (FM) signals (duty cycle: 2.4%), 600-ms continu­ous waves (CW; duty cycle: 5.6%), and 900-ms combinations of the two sound types (Combo; duty cycle: 8.3%). Behavioral responses ranged from no reaction to increased time spent at the water surface, numbers of jumps, hauling out, and swimming speed. At the average received sound pressure levels (SPLsav.rec.) ≤ 158 dB re 1 μPa, and the duty cycles used, mainly the FM sound type caused significant behavioral responses at SPLsav.rec. above 125 dB re 1 μPa. The CW sound type caused minimal response at the SPLsav.rec. offered. The Combo sound type also caused mini­mal response, despite the fact that it contained a longer version of the FM sound type and had a higher duty cycle than the FM sound type. However, the inter-pulse interval was longer in the Combo sound type. The possible effects of signals with different parameters (e.g., duty cycles, signal durations, frequencies, waveforms) are unknown, but the results suggest that, for harbor seals, during peace time exercises and in fisheries, the use of CW and Combo signals is preferred to the use of FM signals (at the signal duration and duty cycles used in the present study).

Key Words: disturbance, fisheries sonar, naval sonar, noise, pinnipeds, Phocid, harbor seal, Phoca vitulina

Document Type: Research Article

DOI: http://dx.doi.org/10.1578/AM.41.4.2015.388

Page Numbers: 388-399