New Directions in Marine Mammal Behavioral Noise Exposure Criteria

New Directions in Marine Mammal Behavioral Noise Exposure Criteria

Marine mammals use sound for virtually every critical life function, from communication to navigation and passive listening for foraging and spatial orientation. Some species have specialized echolocation systems that allow fine-scale orientation and prey detection. While they inhabit naturally noisy environments, added noise from human activities can interfere with these functions by influencing their behavior, physiology, hearing, and ultimately survival. There has been major progress in the scientific understanding of how noise exposure context influences the type and probability of responses, particularly regarding behavioral responses which are the focus here. While this has remained a topic of consideration for half a century, the last two decades have seen both a rapid increase in high quality, controlled measurements of baseline behavioral patterns and resulting understanding of how anthropogenic noise can influence individual and group behavior. Many studies have focused on discrete (acute) exposures and responses in relation to known exposure levels. Some of the early attempts to derive behavioral exposure criteria for predicting response type and severity focused primarily on these kinds of observational and increasingly experimental studies. Recent evolutions of the criteria approaches have begun to include contextual considerations, alternative ways of combining and evaluating data based on operational noise classes rather than hearing-related parameters, and biological vital rates considerations of response parameters. Simultaneously, there have been methodological developments expanding the spatial and temporal scales of potential disturbance studies for different exposure scenarios for local populations. Such studies are challenging to consider with existing acute noise behavioral response criteria and require alternative thinking in evaluating long-term (chronic) disturbances where individual exposure events may matter less. For both acute and chronic noise events, the combined data strongly suggest that all-or-nothing 'thresholds' are inadequate and inconsistent with the available contextual data and the probabilistic nature of responses. There are substantial differences between species, amongst individuals, across situational contexts, and over realistic temporal and spatial scales in terms of exposures. Recent developments and new directions in acute and chronic noise exposure criteria for marine mammals are considered here in a generalized sense, which may be applicable across taxa, industrial noise sources, and regulatory jurisdictions.