Two female harbor seals were exposed for 60min to a continuous one-sixth-octave noise band centered at 32kHz at sound pressure levels of 92 to 152dB re 1 μPa, resulting in sound exposure levels (SELs) of 128 to 188dB re 1 μPa2s. This was part of a larger project determining frequency-dependent susceptibility to temporary threshold shift (TTS) in harbor seals over their entire hearing range. After exposure, TTSs were quantified at 32, 45, and 63kHz with a psychoacoustic technique. At 32kHz, only small TTSs (up to 5.9dB) were measured 1–4min (TTS1–4) after exposure, and recovery was within 1h. The higher the SEL, the higher the TTS induced at 45kHz. Below 176dB re 1 μPa2s, the maximum TTS1–4 was at 32kHz; above 176dB re 1 μPa2s, the maximum TTS1–4 (up to 33.8dB) was at 45kHz. During one particular session, a seal was inadvertently exposed to an SEL of 191dB re 1 μPa2s and at 45kHz, her TTS1–4 was >45dB; her hearing recovered over 4days. Harbor seals appear to be equally susceptible to TTS caused by sounds in the 2.5–32kHz range.

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