Safety criteria for underwater sound produced during offshore pile driving are needed to protect marine mammals. A harbor porpoise was exposed to fatiguing noise at 18 sound pressure level (SPL) and duration combinations. Its temporary hearing threshold shift (TTS) and hearing recovery were quantified with a psychoacoustic technique. Octave-band white noise centered at 4 kHz was the fatiguing stimulus at three mean received SPLs (124, 136, and 148 dB re 1 μPa) and at six durations (7.5, 15, 30, 60, 120, and 240 min). Approximate received sound exposure levels (SELs) varied between 151 and 190 dB re 1 μPa2 s. Hearing thresholds were determined for a narrow-band frequency-swept sine wave (3.9–4.1 kHz; 1 s) before exposure to the fatiguing noise, and at 1–4, 4–8, 8–12, 48, and 96 min after exposure. The lowest SEL (151 dB re 1 μPa2 s) which caused a significant TTS1–4 was due to exposure to an SPL of 124 dB re 1 μPa for 7.5 min. The maximum TTS1–4, induced after a 240 min exposure to 148 dB re 1 μPa, was around 15 dB at a SEL of 190 dB re 1 μPa2 s. Recovery time following TTS varied between 4 min and under 96 min, depending on the exposure level, duration, and the TTS induced.
We thank students Krista Krijger, Tess van der Drift, Amy MacLeod, Ron van Mierlo, Marloe Brouwers, Marjan van den Hoogen, Kiki Ernst, Anne de Bert, Léonie Huijser, Stephanie de Ruijter, Daan Overtoom, and Joyce Davidse; volunteers Brigitte Slingerland, Esther Jansen, Loek van der Drift, Jesse Dijkhuizen and Saskia Roose for assisting in data collection; and Rob Triesscheijn for making some figures. We thank Arie Smink for the design 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 calibrations. We also thank Nancy Jennings (Dotmoth.co.uk), Christ de Jong (TNO), Willem Verboom (JunoBioacoustics), Paul Wensveen (SEAMARCO), Paul Nachtigall (Hawaii Institute of Marine Biology, USA), Dorian Houser (Biomimetica, USA), Michael Ainslie (TNO), René Dekeling (Netherlands Ministry of Infrastructure and Environment), Paul Boers (Netherlands Ministry of Infrastructure and Environment), Vincent Gales (Netherlands Ministry of Defence), and two anonymous reviewers for their comments. Funding was obtained from the Department of Water Management (Netherlands Ministry of Infrastructure and Environment), via IMARES (contact: Tobias van Kooten), and Rijkswaterstaat, Dienst Noordzee (contacts: Martine Graafland and Paul Westerbeek). We thank René Dekeling for his guidance on behalf of the commissioner. The training and testing of the harbor porpoise were authorized by the Netherlands Ministry of Agriculture, Nature and Food Quality, Department of Nature Management; Endangered Species Permit No. FF/75A/2009/039. We thank Jan van Spaandonk (Ministry of Agriculture, Nature and Food Quality) for helping to make the harbor porpoise available.
II. MATERIALS AND METHODS
A. Study animal
B. Study area
C. Background noise, fatiguing noise, and hearing test stimuli SPLmeasurements
D. Fatiguing noise and hearing test signals
1. Fatiguing noise
2. Hearing test signals and selection of test signal frequency
E. Experimental procedure
F. Hearing test procedures
G. Observations and analysis of swimming behavior
H. Analysis of TTShearing threshold and control data
A. Selection of hearing test signal frequency
B. Swimming behavior
C. Prestimulus response rate and control data
D. Effect of SPL and duration of fatiguing noise on TTS and recovery time
IV. DISCUSSION AND CONCLUSIONS
B. TTS and recovery
C. Use of SEL to predict TTS
D. Ecological significance
E. Future research
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