Author:

Keywords:

Science & Technology, Life Sciences & Biomedicine, Marine & Freshwater Biology, Zoology, disturbance, fisheries sonar, naval sonar, noise, pinnipeds, Phocid, harbor seal, Phoca vitulina, UNDERWATER DATA-TRANSMISSION, TONAL SIGNALS, PHOCOENA-PHOCOENA, NOISE, KHZ, SOUNDS, HABITUATION, THRESHOLDS, CALIFORNIA, CETACEANS, 0608 Zoology, 3109 Zoology

Abstract:

The effect of three sonar sound types (around 25 kHz) on the behavior of two harbor seals was quantified on a quiet pool. The behavioral resonse threshold for each sound type was determined by 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 twwo 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 μ Pa, 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).