Evaluating the predictive strength of underwater noise exposure criteria for marine mammals.

The aim of underwater noise exposure criteria in a regulatory context is to identify at what received levels noise-induced effects are predicted to occur, so that those effects may be appropriately considered in an evaluation or mitigation context under the respective regulatory regime. Special emphasis has been given to hearing related impairment of marine mammals due to their high sensitivity to and reliance on underwater sound. Existing regulations of underwater noise show substantial qualitative and quantitative discrepancies. A dataset acquired during an experiment that induced temporary threshold shift (TTS) in a harbor porpoise (Phocoena phocoena) from Lucke, Siebert, Lepper, and Blanchet [(2009). J. Acoust. Soc. Am. 125, 4060-4070] was reanalyzed to see if various exposure criteria predicted TTS differently for high-frequency cetaceans. This provided an unambiguous quantitative comparison of predicted TTS levels for the existing noise exposure criteria used by regulatory bodies in several countries. The comparative evaluation of the existing noise exposure criteria shows substantial disagreement in the predicted levels for onset for auditory effects. While frequency-weighting functions evolved to provide a better representation of sensitivity to noise exposure when compared to measured results at the criteria's onset, thresholds remain the most important parameter determining a match between criteria and measured results.