Temporary hearing threshold shifts and recovery in a harbor porpoise (Phocoena phocoena) and harbor seals (Phoca vitulina) exposed to white noise in a 1/1-octave band around 4 kHz. [Abstract]

To set safety criteria for levels of sounds produced during pile driving for offshore wind parks, temporary hearing threshold shifts sTTSsd were studied in a harbor porpoise and two harbor seals. A psychoacoustic behavioral technique was used to quantify TTS and hearing recovery in the animals exposed to underwater sounds swhite noise in a 1/1-octave band around 4 kHzd. Hearing thresholds were determined once a day for a narrow-band frequency swept sine wave s3.9–4.1 kHzd before and after exposure to the fatiguing noise, which was offered at two sound pressure levels s131 and 119 dB re 1 μPa for the porpoise and 151 and 139 dB re 1 μPa for the sealsd each at four durations s15, 30, 60, and 120 mind. Recovery was quantified by measuring hearing thresholds at 4, 8, 12, and 48 min after the noise exposure. The results show that TTS in harbor porpoises occurred at a sound exposure level threshold approximately 20 dB below the threshold for which TTS occurred in harbor seals