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New Directions in Marine Mammal Behavioral Noise Exposure Criteria2Marine Research of the National Academy of Marine ResearchDOI: 10.29677/MR.202406_4(1).0001 Marine mammals make and use sound for many important biological functions primarily in water, but for the amphibious species (marine carnivores, including seals, sea lions, walruses, polar bears, and sea otters) in air as well. Generating and receiving sound is vitally, arguably centrally, important in their ability to forage, navigate, interact socially, and avoid predators in expansive, dark environments where visual, chemical, and tactile cues may be less useful than for terrestrial mammals. All marine mammals have well-developed auditory systems and can detect a wide range of sounds, often over long distances (Mooney et al., 2012; Reichmuth et al., 2013; Southall et al., 2019a). Most species tested in laboratories can tolerate quite loud sounds without negative effects on their hearing systems (Finneran, 2015; Southall et al., 2019a). Some species demonstrate adaptive vocal behavior to compensate for increases in ambient noise (Guazo et al., 2020). These are resilient animals with millions of years of adaptive history to use sound to survive in what are naturally noisy environments (Erbe et al., 2018). Some of the earliest efforts to quantify behavioral effects in free ranging marine mammals began in the1980s with studies on the impacts of seismic airguns on bowhead (Balaena mysticetus) and gray whales (Eschrichtius robustus). Multiple studies using observational methods of free-ranging animals during ongoing (uncontrolled) surveys demonstrated sustained avoidance of operational areas by whales at distances where seismic pulse received levels (RL) with root-mean-square (RMS) sound pressure levels (SPLs) were 160-170 dB re: 1 %u00b5Pa (Malme et al., 1983, 1984, 1986, 1988; Richardson et al., 1986; Ljungblad et al., 1988). However, responses from bowhead and gray whales using small-scale sources simulating industrial noise revealed quite different response types. Bowhead and gray whales exposed to playback sounds simulating drilling operations suggested much lower RLs of ~120 dB re: 1 %u00b5Pa as an approximate behavioral disturbance (Malme et al., 1984; Richardson et al., 1990). Efforts to apply systematic response \observational studies and small source simulations of operational noise. The National Marine Fisheries Service (NMFS) in the U.S. set auditory impact thresholds and began applying a 160 dB RMS behavioral response threshold for seismic surveys. An expert panel (the High Energy Seismic Survey (HESS) team) was also convened to evaluate the existing data. This panel identified the probabilistic nature of both hearing and behavioral responses, suggesting ranges of exposure criteria, but generally concurred with the 160 dB RMS value as a reasonable 50% probability for seismic surveys and whales. The first systematic and comprehensive efforts to develop exposure criteria across many taxa of marine mammals and sound sources (Southall et al., 2007), much of it based on these early studies, expanded this conclusion. They noted the extensive species and especially contextual differences in responses, such as the differences in responses between feeding and migrating whales and the large differences between actual seismic survey noise and low power simulations with industrial noise playback studies. Southall et al. (2007) noted the importance of the early science in helping to inform the first efforts by the NMFS to develop exposure guidance for regulation but avoided proposing simple step function thresholds for responses. Rather, they developed a systematic severity scale for behavioral responses that was applied to the existing behavioral response data, which clearly demonstrated both the However, anthropogenic noise can have a host of demonstrated deleterious auditory, behavioral, and physiological consequences for marine mammals. These range from detection to orientation indicating awareness to simultaneous or residual disruption of hearing and/or important foraging, social, or predator avoidance behavior, and even extending to mortalities (Southall et al., 2007, 2019a, 2021; Hatch et al., 2016; NAS, 2017; Southall, 2017; Erbe et al., 2018; Duarte et al., 2021; Guan and Brookens, 2023). Observations of some of these kinds of effects for protected, and in some cases endangered, or culturally important species droveinitial scientific and regulatory interest in more systematically documenting and understanding these impacts.1 INTRODUCTION