Seals exposed to intense sounds may suffer hearing loss. After exposure to playbacks of broadband pile-driving sounds, the temporary hearing threshold shift (TTS) of two harbor seals was quantified at 4 and 8 kHz (frequencies of the highest TTS) with a psychoacoustic technique. The pile-driving sounds had: a 127 ms pulse duration, 2760 strikes per h, a 1.3 s inter-pulse interval, a ∼9.5% duty cycle, and an average received single-strike unweighted sound exposure level (SELss) of 151 dB re 1 μPa2s. Exposure durations were 180 and 360 min [cumulative sound exposure level (SELcum): 190 and 193 dB re 1 μPa2s]. Control sessions were conducted under low ambient noise. TTS only occurred after 360 min exposures (mean TTS: seal 02, 1–4 min after sound stopped: 3.9 dB at 4 kHz and 2.4 dB at 8 kHz; seal 01, 12–16 min after sound stopped: 2.8 dB at 4 kHz and 2.6 dB at 8 kHz). Hearing recovered within 60 min post-exposure. The TTSs were small, due to the small amount of sound energy to which the seals were exposed. Biological TTS onset SELcum for the pile-driving sounds used in this study is around 192 dB re 1 μPa2s (for mean received SELss of 151 dB re 1 μPa and a duty cycle of ∼9.5%).

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