| Autor: |
Kastelein RA; Sea Mammal Research Company (SEAMARCO), Julianalaan 46, 3843 CC Harderwijk, The Netherlands., Helder-Hoek L; Sea Mammal Research Company (SEAMARCO), Julianalaan 46, 3843 CC Harderwijk, The Netherlands., Van de Voorde S; Sea Mammal Research Company (SEAMARCO), Julianalaan 46, 3843 CC Harderwijk, The Netherlands., von Benda-Beckmann AM; TNO Acoustics and Sonar, Oude Waalsdorperweg 63, 2597 AK, The Hague, The Netherlands., Lam FA; TNO Acoustics and Sonar, Oude Waalsdorperweg 63, 2597 AK, The Hague, The Netherlands., Jansen E; TNO Acoustics and Sonar, Oude Waalsdorperweg 63, 2597 AK, The Hague, The Netherlands., de Jong CAF; TNO Acoustics and Sonar, Oude Waalsdorperweg 63, 2597 AK, The Hague, The Netherlands., Ainslie MA; TNO Acoustics and Sonar, Oude Waalsdorperweg 63, 2597 AK, The Hague, The Netherlands. |
| Abstrakt: |
In seismic surveys, reflected sounds from airguns are used under water to detect gas and oil below the sea floor. The airguns produce broadband high-amplitude impulsive sounds, which may cause temporary or permanent threshold shifts (TTS or PTS) in cetaceans. The magnitude of the threshold shifts and the hearing frequencies at which they occur depend on factors such as the received cumulative sound exposure level (SELcum), the number of exposures, and the frequency content of the sounds. To quantify TTS caused by airgun exposure and the subsequent hearing recovery, the hearing of a harbor porpoise was tested by means of a psychophysical technique. TTS was observed after exposure to 10 and 20 consecutive shots fired from two airguns simultaneously (SELcum: 188 and 191 dB re 1 μPa 2 s) with mean shot intervals of around 17 s. Although most of the airgun sounds' energy was below 1 kHz, statistically significant initial TTS 1-4 (1-4 min after sound exposure stopped) of ∼4.4 dB occurred only at the hearing frequency 4 kHz, and not at lower hearing frequencies tested (0.5, 1, and 2 kHz). Recovery occurred within 12 min post-exposure. The study indicates that frequency-weighted SELcum is a good predictor for the low levels of TTS observed. |
