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New Directions in Marine Mammal Behavioral Noise Exposure Criteria9Marine Research of the National Academy of Marine ResearchDOI: 10.29677/MR.202406_4(1).0001 Studies of both discrete exposure-response and medium-to-long-term population level responses (e.g.,distribution, broad scale acoustic behavior changes) are needed and can be insightful if properly designed. Suchstudies need to consider not only distinct noise-related activities, key individual covariates (e.g., sex/age class, health status), and concurrent and potentially interacting stressors that may amplify, potentially in non-linear ways, acoustic disturbance (Pirotta et al., 2022a; Tyack et al., 2022). It should be clearly recognized that this will require fundamentally different analytical methods than either the simple response severity assessment for discrete effects developed by Southall et al. (2007) and adapted by Southall et al. (2021) or the highly complex, model-based, quantitative multi-stressor analyses for results to be integrated more broadly in efforts to predict response type, occurrence, severity, and consequence for application in real-world decision making. Both types of assessment, however, require more comprehensive, detailed, and consistently reported information on exposure contexts, received noise metrics, ecological conditions, and detailed descriptors of individual and/or population response metrics. Initial efforts to outline the key parameters in developing explicit criteria for chronic exposures and guidingthe design and studies of them were made by Southall et al. (2021), but clearly further development and synthesis are needed. Additional analytical approaches (beyond the acute severity scale) for broader spatial scale population studies are being developed, particularly for regulatory assessments of cumulative impacts and in regulatory paradigms where the focus is at the population level (Palialexis et al., 2021). Expertise from researchers studying long-term effects of whale watching and other long-term disturbances, life history population models of energetic consequences of disturbance, and models of interacting physiological and acoustic exposure impacts should be brought to bear. Key considerations of acoustic exposure for such longterm studies and exposure criteria should lean heavily on advances in soundscape analyses (McKenna et al., 2021) with metrics for variance in both ambient noise and ephemeral exposure events. Such data require systematic and sustained passive acoustic monitoring in key habitats. Important environmental covariates of new exposure criteria for chronic disturbance in addition to acoustic exposure are also clearly needed, including stressors related to prey distribution, pollutants, predator exposure, and a host of factors associated with climate change. New approaches applying risk assessment methods that focus on the spatial and temporal intersection of activities and distributions that incorporate population and life history parameters in transparent, commonsense applications may also provide practical perspectives for policy and management applications (Southall et al., 2023b). Life history aspects of species exposed to chronic stressors are also critical considerations, includingcapital or income foraging strategies, body size, reproductive patterns, and habitat site fidelity. Finally, responsetypes that should be particularly considered in future chronic disturbance criteria include long-term changes in habitat utilization, overall changes in group size/structure, timing or patterns of reproduction, and patterns and rates of predation or other forms of mortality.inconsistent with the best scientific information available. It is also clear that, while they were initially coupled in some regards (Southall et al., 2007), different approaches and some segregation of exposure criteria methods for auditory and behavioral effects are needed (Southall et al., 2019b; 2021). It is simply impractical and misinformed to seek to account for the high degree of variability that exists given the individual, population, or species differences in response in different contexts. Rather, at least for acute responses, some aggregation of response assessment within noise-specific category types using common, ecologically-derived severity assessments (Southall et al., 2021) to identify exposure-response functions for highly sensitive, intermediately sensitive, and highly tolerant species is likely a more practical and meaningful approach for regulatory applications. The revised behavioral response severity metrics presented in Southall et al. (2021) provide more robust and clear recommendations for acoustic exposure and behavioral response type and severity presented in terms of vital rates for acute events. However, they are clearly limited, as noted, in terms of applications for longer-term exposures.