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Abstract: Low-frequency sonar systems that produce sound in the 1.33 to 1.43 kHz frequency band are deployed from navy helicopters (HELRAS [Helicopter Long Range Active Sonar]) and vessels to detect submarines, and the sounds vary in spectrum, duration, and inter-pulse interval depending on the detection tasks. The sounds produced may affect the behavior of harbor porpoises (Phocoena phocoena) within a certain distance from the sound source. The goal of this study was to determine whether sonar sounds with four different harmonic contents and amplitude envelopes had different effects on harbor porpoise behavior. The sounds all had the same duration (1.25 s) and source level (107 dB re 1 μPa), and were produced in a series with regular inter-pulse intervals (14.4 s; duty cycle: 8%). A porpoise in a 12 × 8 m quiet pool was exposed to a 30-min series of each of the four sonar sounds (115 sounds/30 min). Mean received sound pressure level (SPL) in the pool was ~97 dB re 1 μPa for all exposures. During test sessions with each of the four sounds, the porpoise’s mean distance to the transducer remained the same, and his swimming speed and number of surfacings (respirations) were only slightly higher than during baseline sessions without sounds. The downsweep caused a smaller behavioral effect than the continuous wave sounds. It is important to realize that the spectrum and SPL received by an animal determine whether it responds to a sound or not, and not the spectrum and SPL near a source.
Key Words: anthropogenic noise, behavioral response, disturbance, mitigation, naval sonar, odontocete
Page Numbers: 632-645