Marine Mammal Noise Exposure Criteria: Assessing the Severity of Marine Mammal Behavioral Responses to Human Noise

Major progress has been made since the publication of noise exposure criteria by Southall et al. (2007) in addressing the probability and severity of marine mammal behavioral responses to measured noise exposures. New methodological developments for studying behavioral responses have broadened the spatial, temporal, and population scales of poten-tial disturbance studies and expanded scientific data on responses of marine mammals (or lack thereof) to various human noise exposure scenar-ios. Experimental and observational studies have substantially expanded the resolution, parameters, and contexts for understanding individual and group responses to discrete noise events. The com-bined data strongly suggest that efforts to derive simple all-or-nothing thresholds for single noise exposure parameters (e.g., received noise level) and behavioral responses across broad taxonomic and sound categories can lead to significant errors in predicting effects that are fundamentally incon-sistent with the probabilistic nature of responses. Differences between species, among individuals, across situational contexts, and with the tempo-ral and spatial scales over which exposures occur lead to variability in the probability and severity of behavioral responses. Studies that account for such factors and the variability they cause can provide far more accurate probability functions for predict-ing effects and can reduce variabilities related to exposure level and response. To that end, several new approaches are developed here for evaluating response severity in laboratory and field conditions in terms of effects on vital rates. These are applied to selected studies of marine mammal behavioral response to demonstrate their application in more consistently addressing acute exposure contexts for individuals or discrete groups. Needs for new approaches and transparent processes are identified for addressing sustained and/or repeated noise exposures on population scales.