| Summary: | 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 mu Pa [mean received sound exposure level (SEL) range: 162-189 dB re 1 mu Pa(2)s]. 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 mu Pa(2)s and at 50 kHz with SELs of >= 174 dB re 1 mu Pa(2)s. At 63 kHz, TTS1-4 occurred with SELs >= 186 dB re 1 mu Pa(2)s. In F01, significant TTS12-16 (12-16 min post exposure) occurred only at 50 kHz with SELs of >= 177 dB re 1 mu Pa(2)s. 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 mu Pa(2)s); 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.
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