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Temporary Threshold Shift in a Second Harbor Porpoise (Phocoena phocoena) After Exposure to a One-Sixth-Octave Noise Band at 1.5 kHz and a 6.5 kHz Continuous Wave
Abstract: To determine whether susceptibility to noise-induced temporary hearing threshold shift (TTS) differs between individual harbor porpoises (Phocoena phocoena), studies with an 8-year-old male (M02) were repeated by exposing a 9-year-old female (F05) to similar fatiguing sounds. F05 was exposed for one hour to a continuous one-sixth-octave noise band (NB) centered at 1.5 kHz at six sound pressure levels (SPLs; resulting sound exposure level [SEL] range: 180 to 201 dB re 1 µPa2s), and to a 6.5 kHz continuous wave (CW) at 4 to 10 SPLs (resulting SEL range: 139 to 184 dB re 1 µPa2s). To quantify TTS, hearing thresholds for 1.5, 2.1, 3, 6.5, 9.2, and 13 kHz signals were determined before and after exposures. After exposure to the NB at 1.5 kHz, the lowest SELs resulting in significant TTS1-4 were 186 dB re 1 µPa2s for 1.5 kHz (1.0 dB), 194 dB re 1 µPa2s for 2.1 kHz (4.7 dB), and 190 dB re 1 µPa2s for 3 kHz (1.5 dB). The highest TTS1-4 was 9.3 dB, measured at 2.1 kHz after exposure to SEL 201 dB re 1 µPa2s. After exposure to the 6.5 kHz CW, the lowest SELs resulting in significant TTS1-4 were 145 dB re 1 µPa2s for 6.5 kHz (2.9 dB), 178 dB re 1 µPa2s for 9.2 kHz (7.3 dB), and 180 dB re 1 µPa2s for 13 kHz (6.4 dB). Six dB TTS was elicited in F05 at 2.1 kHz after exposure to the NB at 1.5 kHz at SEL 198 dB re 1 µPa2s, and in M02 at 1.5 kHz after exposure to 1 to 2 kHz downsweeps at SEL ~190 dB re 1 µPa2s. The difference in susceptibility to TTS may be due to individual differences in TTS susceptibility and/or differences in the fatiguing sounds (i.e., sweeps, CWs, and NBs). Susceptibility to TTS was similar in both porpoises after exposure to a 6.5 kHz CW: 6 dB TTS was elicited at 9.2 kHz in both animals after exposure to SEL ~176 dB re 1 µPa2s.
Key Words: anthropogenic noise, audiogram, frequency weighting, hearing, hearing damage, hearing sensitivity, odontocete, temporary threshold shift, TTS
Page Numbers: 431-443