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Temporary hearing threshold shift in a harbor porpoise (Phocoena phocoena) after exposure to multiple airgun sounds

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Author: Kastelein, R.A. · Helder-Hoek, L. · Voorde, S. van de · Von Benda-Beckmann, A.M. von · Lam, F.P.A. · Jansen, E. · Jong, C.A.F. de · Ainslie, M.A.
Type:article
Date:2017
Publisher: Acoustical Society of America
Source:Journal of the Acoustical Society of America, 4, 142, 2430-2442
Identifier: 781909
Keywords: Mammals · Frequency contents · Frequency weighted · Hearing threshold · Impulsive sounds · Phocoena phocoena · Reflected sounds · Sound exposure levels · Threshold shifts · Audition · 2015 Observation, Weapon & Protection Systems · AS - Acoustics & Sonar · TS - Technical Sciences

Abstract

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 μPa2s) with mean shot intervals of around 17 s. Although most of the airgun sounds' energy was below 1 kHz, statistically significant initial TTS1-4 (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. © 2017 Acoustical Society of America.