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New Directions in Marine Mammal Behavioral Noise Exposure Criteria4Marine Research of the National Academy of Marine ResearchDOI: 10.29677/MR.202406_4(1).0001 This progress in evolving approaches for quantifying and applying science in revising methods for acutestudies is a needed and positive step. However, in many cases, noise exposure events do not occur in isolation. Many events are repeated and most that occur in developed areas occur in cases where multiple exposures of different types may be common. Consequently, there has been considerable interest and progress in quantifying the individual severity and consequences of responses and evaluating potential population consequences of exposure (New et al., 2014; Pirotta et al., 2021, 2022a). Many well-conducted studies have focused on potential changes at the level of local populations over the period of months, seasons, and years. For instance, broadscale monitoring surveys have related cetacean distribution and behavior to longer-term presence or occurrence of seismic surveys (Thompson et al., 2013; Pirotta et al., 2014; Kyn et al., 2019) and impact pile driving (Madsen et al, 2006; Bailey et al., 2010; see: Thompson et al., 2020). Such broad-scale observational studies lack the experimental control and individual resolution required to identify some finer-scale responses and generally fail to differentiate short-term responses from those to other stimuli. However, they have considerable advantages over short-term experimental studies, by offering broader time and space scale perspectives on changes in habitat use and associated significant behavior such as foraging. It has proven challenging, and is likely inappropriate, to apply the acute event exposure-response severity assessment to such studies in the development of noise exposure criteria (Southall et al., 2021). New and evolving approaches are needed with which to evaluate and apply existing and new experimental and observational findings on the behavioral responses of marine mammals to understand and mitigate the effects of human noise on protected species in real-world applications. The substantial evolution of exposure criteria for acute effects are discussed here, both in terms of how they may inform regulatory applications for discrete noise events, but also for how they differ from and obviate the need for the development of more systematic approaches with broader, international applications to evaluating and regulating noise on longer time and broader spatial scales. patterns of response type and probability have emerged. For some species, noise exposure (RL) -response relationships appear to exist in some conditions for exposure level and response probability in killer whales (Miller et al., 2014; Southall et al., 2023a). Yet state-dependent responses appear to be more important drivers than RL for other species (Goldbogen et al., 2013). Some species appear relatively tolerant of noise exposure behaviorally, including long-finned pilot whales (Globicephala melas; Antunes et al., 2014) and humpback whales (Megaptera novaeangliae; Dunlop et al., 2017). These kinds of studies, as well as well-documented observational studies of exposure and response of individuals or groups of animals (Moretti et al., 2014) have provided an increasingly robust basis for which behavioral response criteria that have been developed may be applied to derive and adapt noise exposure criteria (Southall et al., 2021). This new scientific foundation has supported evolution of regulatory approaches for some discrete (acute) noise sources. Specifically, within the U.S., the NMFS has adopted probabilistic risk functions for regulating certain military sonar systems as well as species and location-specific mitigation approaches (including site closures), based on this surge of recent scientific information. Interestingly, the risk functions for MFAS developed by the U.S. Navy and adopted by the NMFS have a bi-phasic probability pattern indicative of the contextual and linear contextual patterns predicted by Ellison et al. (2012). Given the extensive research progress in evaluating noise impacts on the behavior of marine mammals, the increasing application of risk assessment methods, and emerging policy needs, there have been extensive evolutions in noise exposure criteria for acute effects since the publication of the first such criteria developed broadly for marine mammals by Southall et al. (2007). A fundamental aspect of the Southall et al. (2007)2 EVOLUTIONS IN NOISE EXPOSURE CRITERIA FORBEHAVIORAL RESPONSES