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PEARL HARBOR, Hawaii - A newly released scientific report demonstrates the viability of a new method to estimate received sound levels during real scenarios and analyzes movements of satellite-tagged individuals of three species of marine mammals exposed to Navy mid-frequency active sonar around Kauai's Pacific Missile Range Facility (PMRF).
"This is exciting news in several ways, not least of which is the promise this new integrated approach holds for learning how sonar affects marine mammals," said Julie Rivers, natural and marine resources program manager for the U.S. Pacific Fleet, which funded the study as part of its Marine Mammal Monitoring Program.
The report is co-authored by Robin Baird and Daniel Webster of Cascadia Research, Brandon Southall of Southall Environmental Associates, and Stephen Martin of the U.S. Navy. Morgan Richie, the Navy technical representative at Naval Facilities Engineering Command Pacific, provided technical oversight for the project.
On five occasions preceding Navy training events the researchers tagged a total of 23 marine mammals. The data from the satellite tags enabled them to track points along the animals' path and, in some cases, due to more sophisticated tags, their dive movements. The range facility's hydrophones, on the ocean floor northwest of Kauai, were used to record data on the actual levels of sound energy from sonar transmissions. That data enabled the scientists to use mathematical modeling to produce estimates of the range of sound levels to which some of the animals were exposed and to assess their responses.
Some tags didn't provide enough information, as often happens, and many of the tagged animals were not on or near the range during the brief periods when sonar was being used. Nonetheless, received sound levels were compiled and movements tracked for four animals: two rough-toothed dolphins, a bottle-nose dolphin and a short-finned pilot whale.
The researchers found that the bottlenose dolphin showed no large-scale movements out of the area during sonar exposures, and a short-finned pilot whale actually moved toward areas of higher sonar levels during the third day of a 3-day period of regular mid-frequency active sonar use. While the data from the rough-toothed dolphins are more limited than those for the bottlenose dolphin and the short-finned pilot whale, results are similar in that the animals did not make broad scale movement into areas where received sound levels would have been lower.
"The sample is obviously small, but we are encouraged by the prospects for using this integrated approach to learn more about the behavior of sound in the water and how it affects marine life," said Rivers.
The report is available at http://www.cascadiaresearch.org/hawaii/Bairdetal2014_PMRFexposure.pdf.