Temporary hearing threshold shift in harbor seals (Phoca vitulina) due to a one-sixth-octave noise band centered at 40 kHz

As part of a series of studies to determine frequency-dependent susceptibility to temporary hearing threshold shifts (TTS), two female harbor seals (F01 and F02) were exposed for 60 min to a one-sixth-octave noise band centered at 40 kHz at mean sound pressure levels ranging from 126 to 153 dB re 1 μPa [mean received sound exposure level (SEL) range: 162–189 dB re 1 μPa2s]. TTSs were quantified at 40, 50, and 63 kHz within 1–4 min of the exposure for F02 and within 12–16 min of the exposure for F01. In F02, significant TTS1–4 (1–4 min post exposure) occurred at 40 kHz with SELs of ≥183 dB re 1 μPa2s and at 50 kHz with SELs of ≥174 dB re 1 μPa2s. At 63 kHz, TTS1–4 occurred with SELs ≥186 dB re 1 μPa2s. In F01, significant TTS12–16 (12–16 min post exposure) occurred only at 50 kHz with SELs of ≥177 dB re 1 μPa2s. The highest TTSs (27.5 dB in F02, 29.8 dB in F01) occurred at 50 kHz, one-third of an octave above the fatiguing sound's center frequency (SEL = 189 dB re 1 μPa2s); recovery took 2 days in F02 and 4 days in F01. In most other cases, recovery was within 1 h. The seals have a similar susceptibility to TTS from 4 to 40 kHz.