Cetacean noise criteria revisited in the light of proposed exposure limits for harbour porpoises

• Published in: Marine pollution bulletin 2015-01, Vol.90 (1-2), p.196-208
• Main Authors: Tougaard, Jakob, Wright, Andrew J., Madsen, Peter T.
• Format: Article
• Language: English
• Subjects: Acoustic Stimulation; Animals; Behavioural response; Bottle-Nosed Dolphin - physiology; Cetacea; Environmental Exposure - legislation & jurisprudence; Frequency weighting; Hearing; Impact assessment; Light; Marine; Noise; Phocoena - physiology; Porpoises - physiology; Sound; Sound Spectrography; Temporary threshold shift; Underwater noise; United States
• ISSN: 0025-326X; 1879-3363
• DOI: 10.1016/j.marpolbul.2014.10.051

•The current acoustic exposure criteria for marine mammals are in need of revision.•Severity of behavioural responses does not correlate well with long term consequences for animals.•Review of TTS experiments on porpoises suggests that inverse audiogram weighting is appropriate.•Thresholds for acoustic avoidance behaviour in porpoises are also correlated with audibility.•Thresholds can be normalised as rms sound pressure levels averaged over 125ms. The impact of underwater noise on marine life calls for identification of exposure criteria to inform mitigation. Here we review recent experimental evidence with focus on the high-frequency cetaceans and discuss scientifically-based initial exposure criteria. A range of new TTS experiments suggest that harbour and finless porpoises are more sensitive to sound than expected from extrapolations based on results from bottlenose dolphins. Furthermore, the results from TTS experiments and field studies of behavioural reactions to noise, suggest that response thresholds and TTS critically depend on stimulus frequency. Sound exposure levels for pure tones that induce TTS are reasonably consistent at about 100dB above the hearing threshold for pure tones and sound pressure thresholds for avoidance reactions are in the range of 40–50dB above the hearing threshold. We propose that frequency weighting with a filter function approximating the inversed audiogram might be appropriate when assessing impact.