Safety criteria for underwater sounds from offshore pile driving are needed to protect marine mammals. As a first step toward understanding effects of impulsive sounds, two harbor seals were exposed to octave-band white noise centered at 4 kHz at three mean received sound pressure levels (SPLs; 124, 136, and 148 dB re 1 μPa) at up to six durations (7.5, 15, 30, 60, 120, and 240 min); mean received sound exposure level (SEL) range was 166–190 dB re 1 . Hearing thresholds were determined before and after exposure. Temporary hearing threshold shifts (TTS) and subsequent recovery were quantified as changes in hearing thresholds at 1–4, 4–8, 8–12, 48, and 96 min after noise exposure in seal 01, and at 12–16, 16–20, 20–24, 60, and 108 min after exposure in seal 02. Maximum TTS (1–4 min after 120 min exposure to 148 dB re 1 μPa; 187 dB SEL) was 10 dB. Recovery occurred within ∼60 min. Statistically significant TTSs (>2.5 dB) began to occur at SELs of ∼170 (136 SPL, 60 min) and 178 dB re 1 (148 SPL, 15 min). However, SEL is not an optimal predictor of TTS for long duration, low SPL continuous noise, as duration and SPL play unequal roles in determining induced TTS.
We thank students Ron van Mierlo, Tess van der Drift, Marjan van den Hoogen, Marloe Brouwers, Anne de Bert, Kiki Ernst, Juul Olthuis, Léonie Huijser, Stephanie de Ruijter, Daan Overtoom, and Joyce Davidse, and volunteers Brigitte Slingerland, Esther Jansen, Loek van der Drift, Krista Krijger, Jesse Dijkhuizen, and Saskia Roose for their help in collecting the data, and Rob Triesscheijn for making some of the graphs. We thank Arie Smink for the design, construction, and maintenance of the electronic equipment. We thank Bert Meijering (Topsy Baits) for providing space for the SEAMARCO Research Institute. Erwin Jansen (TNO) conducted the acoustic calibration measurements. We also thank Willem Verboom (JunoBioacoustics), Christ de Jong (TNO), Paul Wensveen (SEAMARCO), Nancy Jennings (Dotmoth.co.uk), Paul Nachtigall (Hawaii Institute of Marine Biology, USA), Dorian Houser (Biomimetica, USA), René Dekeling, Suzan van Lieshout, and Paul Boers (Netherlands Ministry of Infrastructure and Environment), Vincent Gales (Netherlands Ministry of Defence), and two anonymous reviewers for their valuable constructive comments on this manuscript. Funding for this project was obtained from the Center of Water Management (Netherlands Ministry of Infrastructure and Environment), and Rijkswaterstaat, Dienst Noordzee. We thank René Dekeling, Martine Graafland, and Paul Westerbeek for their guidance on behalf of the commissioner. We thank Ecomare for making the harbor seals available for this project. The seals’ training and testing were conducted under authorization of the Netherlands Ministry of Agriculture, Nature and Food Quality, Department of Nature Management, with Endangered Species Permit FF/75A/2009/039.
II. MATERIAL AND METHODS
A. Study animals
B. Study area
C. Background noise, fatiguing noise, and hearing test signal SPL calibration measurements
D. Fatiguing noise and hearing test signals
1. Fatiguing noise
2. Hearing test signals and selection of test signal frequency
E. Hearing test procedures
F. Experimental procedure
G. Observations and analysis of swimming behavior
H. Analysis of TTS,hearing threshold, and control data
A. Swimming behavior
B. Selection of hearing test signal frequency
C. Effect of SPL and duration of fatiguing noise on TTS and recovery time
B. TTS and recovery
C. Use of SEL to predict TTS
D. Effect of aerial and underwater fatiguing noises
E. Ecological significance
F. Future research
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