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New Directions in Marine Mammal Behavioral Noise Exposure Criteria6Marine Research of the National Academy of Marine ResearchDOI: 10.29677/MR.202406_4(1).0001 For field contexts with free-ranging marine mammals, response severity was segregated into categoriesrelated to foraging, survival, and reproduction, which may differentially affect vital rates. The overall approach retained discrete behavioral categories along an ordinal scale of increasing severity with descriptors of response type, magnitude, and duration. The objective was to expand the original response descriptions and identify thoseof increasing severity along three parallel severity tracks relevant to vital rates, defining behaviors that may affect individual fitness and consequently population parameters. The three tracks evaluate behavioral responsesrelated to: survival (including effects on defense, resting, social interactions, and navigation); reproduction (including mating and parenting behaviors); and foraging (encompassing search, pursuit, capture, and consumption of prey). Where the acute exposure-response severity scale-based assessment approach really falls short is in the evaluation of repeated or sustained exposures for aggregations and/or local populations of animals on broader spatial and temporal scales. As Southall et al. (2021) were clear in evaluating and applying the revised acute exposure severity scales (described in greater detail below) to longer-term (e.g., seasonal, annual) studies with fewer discrete exposures to specific individuals, there are limitations in the applicability of this approach for these scenarios. For instance, where the unit of analysis in a longer-term study is a local population, this would be reduced to a single observation as applied to these acute severity scales. This may result in inappropriate or unfair comparisons with severity assessments of acute exposure studies where a defined number of known exposed individuals are weighted as that number of discrete observations. Clearly, other approaches are needed to evaluate relationships between short-term acute exposures and population effects and chronic stress (Lusseau et al., 2014; Simmonds et al. 2014). Given the wide range of spatial and temporal scales of exposure and potential disturbance over which researchers are measuring, there is an emerging need to extend and evolve the Advances made in the Southall et al. (2021) adaptation of behavioral response severity assessments haveseveral key implications. First, they fundamentally segregate the evaluation of field and highly contextual laboratory studies, providing derived approaches for each. Second, for field applications, they provide more prescriptive aspects of temporal duration of effect and ways of evaluating different outcomes in terms of behaviors differentially related to fitness. Finally, they call for the design, execution, and reporting of data from controlled experiments, focusing as much as possible on actual, realistic exposures and sources, to include an array of exposure and contextual parameters that will support more sophisticated multi-variate probabilistic response functions. Each of these measures are intended to improve the empirical basis and validation of future exposure-response functions, to enable data-driven selection of appropriate species and source groupings for such functions, and hopefully to enable sufficient exposure and contextual information to allow results to beapplied and interpreted in broader international contexts. Going to Scale: Initial Progress and Needed Studies and Criteria for Broader Spatial and Temporal Scales For captive marine mammals, this included discrete consideration of responses from untrained and trained behaviors. The separation of severity scales for captive and field settings was because captive studies of marine mammal behavioral responses may be limited in their application to free-ranging scenarios given the very different environmental and motivational contexts. A training paradigm makes it possible to measure the aversiveness of exposures to noise very precisely, and negative responses of captive animals can be observed in greater detail than is possible with individuals observed for short periods with remote monitoring equipment. But probabilistic response relationships as a function of noise exposure for captive animals that have been reinforced in training to respond to signals may be usefully compared to free-ranging animals that experience positive and/or negative reinforcement for responses to ambient signals in the wild. Narrative heuristic descriptions were provided for untrained responses to provide some insight into general overall comparisons with field observations of behavioral response, enabling consideration of studies with different methods.