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 (TTSs) 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 (white noise in a 1/1‐octave band around 4 kHz). Hearing thresholds were determined once a day for a narrow‐band frequency swept sine wave (3.9–4.1 kHz) before and after exposure to the fatiguing noise, which was offered at two sound pressure levels (131 and 119 dB re 1 μPa for the porpoise and 151 and 139 dB re 1 μPa for the seals) each at four durations (15, 30, 60, and 120 min). 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.