![]() There may also be “hidden” impacts of sonar and exercises not readily observable (e.g., stress responses). Strandings may be undetected, or be unlikely to be observed because of a lack of search effort or due to coastal topography or characteristics. ![]() Although there are many stranding events that have occurred coincident with the presence of naval vessels or exercises, it is important to emphasize that even the absence of strandings in a region does not equate to an absence of deaths, i.e., absence of evidence does not mean evidence of absence. There is strong scientific evidence to suggest that a wide range of whale, dolphin and porpoise species can also be impacted by sound produced during military activities, with significant effects occurring at received levels lower than previously predicted. Changes in beaked whale behavior, including evasive maneuvering, have been recorded at received levels below <100 dB re 1 μPa (rms) and mass stranding may occur at received levels potentially as low as 150–170 dB re 1 μPa. In particular, there have been several mass strandings in the northern Indian Ocean coincident with naval exercises-including one of the largest (200–250 dolphins)-which have received little attention. and Delphinus delphis), and harbor porpoises ( Phocoena phocoena). The list of species for which mass strandings have been linked to naval exercises has also increased to include other beaked whales, dwarf and pygmy sperm whales ( Kogia spp.), pilot whales ( Globicephala spp.), several dolphin species ( Stenella sp. Subsequently attention has been drawn to other mass strandings coincident with naval exercises, including events preceding the 2000 mass stranding. This was the first time that the US Government determined a stranding to be the result of mid-frequency active sonar use. The risks military sonar poses to cetaceans received international attention with a highly-publicized mass stranding of Cuvier's beaked whales ( Ziphius cavirostris), Blainville's beaked whales ( Mesoplodon densirostris), and northern minke whales ( Balaenoptera acutorostrata) in the Bahamas in 2000. ![]() Environmental Science and Policy, George Mason University, Fairfax, VA, United States. ![]()
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