Page 52 - Summer 2021

FEATURED ARTICLE
Evolutions in Marine Mammal Noise Exposure Criteria
Brandon L. Southall
Foreword: The work summarized here represents the col- lective efforts of an international, interdisciplinary group of scientific experts to address potential underwater sound impacts on marine mammals. The original group included Roger Gentry (who conceived of and convened the origi- nal panel), Ann Bowles, William Ellison, James Finneran, Charles Greene Jr., David Kastak, Darlene Ketten, James Miller, Paul Nachtigall, John Richardson, Brandon South- all, Jeanette Thomas, and Peter Tyack. Colleen Reichmuth, Doug Nowacek, and Lars Bejder were added subsequently. All of these individuals contributed substantively to the evolving criteria for marine mammal noise exposure described herein.
Marine Mammal Noise Exposure Criteria: Emerging Needs
More than half a century ago, concerns were raised about the potential for human industrial noise to mask whale communication (Payne and Webb, 1971). In the ensuing decades, multiple, increasingly complex tech- nological and scientific approaches have been developed to assess whether and how human noise can negatively affect ocean wildlife. In national jurisdictions and inter- national agreements, threatened and endangered species, which include most marine mammals, are often afforded legal protections intended to mitigate the noise impacts of human activities. Much research has thus centered on marine mammals. Fair or not, “charismatic mega- fauna” also garner more public attention than other taxa, although recent trends are broadening consideration to fishes and invertebrates (e.g., Hawkins et al., 2015).
Marine mammals are a taxonomically and ecologically diverse aggregation of species, inhabiting coastal and open ocean waters from pole to pole. (For an excellent over- view of marine mammals and sound, see www.dosits.org.) They include the fully aquatic cetaceans, composed of large baleen whales (mysticetes; see bit.ly/3fpPOz8); the
“toothed” whales, dolphins, and porpoises (odonotocetes; see bit.ly/3dfFYNv); the sirenians (manatees and dugongs; see bit.ly/3fnKxs2); the amphibious pinnipeds (true seals, sea lions, and walrus; see bit.ly/2QB06SD); and other marine carnivores (otters and polar bears). Marine mam- mals are exposed to diverse impulsive, continuous, and intermittent noise sources. This ever-changing situation creates myriad challenges for deriving comprehensive, empirically based exposure criteria for such a breadth of species and their potential risk from different sources. Extensive data gaps remain in many key areas, some of which (e.g., direct measurements of auditory effects of noise for baleen whales) are difficult to envision ever fill- ing. However, great progress has been made by a large and growing community of scientists working on these issues.
Some species appear particularly sensitive to acoustic dis- turbance, including beaked whales (see bit.ly/3d9Tu5m) that have stranded following exposure to military mid- frequency sonar (e.g., D’Amico et al., 2009). Events in Greece, the Bahamas, Canary Islands, and other locations fueled awareness of how noise can harm marine mam- mals (Ketten, 2014). Increasing attention and ensuing legal battles led to more and broader research efforts to obtain a better scientific basis for regulatory oversight and legal compliance. Scientists now recognize that rare, yet dra- matic and potentially locally important, stranding events are just one among many potential effects of human noise. Equally serious effects may parallel those seen for humans and land mammals, such as noise-induced hearing losses, behavioral disturbances, communication disruption or masking, and physiological stress (see Southall, 2017). There is also the challenge, given the diversity of species and their hearing abilities, that sounds that are noisome to one species may be irrelevant or even inaudible to another.
Researchers and regulatory agencies have grappled for decades with the complexities of establishing “thresholds”
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52 Acoustics Today • Summer 2021 | Volume 17, issue 2
https://doi.org/10.1121/AT.2021.17.2.52