NOAA Fisheries employs a set of in-water noise exposure guidelines that establish regulatory thresholds for ocean actions that impact marine mammals. These are established based on two impact criteria: Level A – a physiological impact including “Permanent Threshold Shift” (PTS), and/or tissue damage, and/or mortality, and Level B – a behavioral impact or disruption. Recently the Level A exposure thresholds were reconciled to the frequency-dependent hearing sensitivities of five classes of marine mammals based on work done more than a decade ago (Southall et al. 2007). Since that time much more work has been published on behavioral impacts of various noise exposures, and consideration of more variables such as frequency-dependent noise propagation characteristics, cumulative, concurrent, and continuous exposures, and noise impacts on marine soundscapes have entered into the discussion – but have not been incorporated into the NOAA Fisheries guidelines.

Some of these variables will be highlighted, suggesting that it may be time to reevaluate the thresholds for Level B exposures.

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