Navy and U.S. National Oceanic and Atmospheric Administration (NOAA) researchers concluded Oct. 2 their second year of field investigation on the effects of sound on whales during a Behavioral Response Study (BRS) at the Bahamas' Atlantic Undersea Test and Evaluation Center (AUTEC).
Despite storms which forced the evacuation of scientists for roughly a quarter of the 50-day study period, researchers and technicians succeeded in placing acoustic listening tags on six whales.
They "played back" simulated mid-frequency sonar sounds and control sounds (sounds consisting of random noise in similar frequency bands) to a total of six tagged whales from four species - beaked, pilot, melon-headed and false killer whales.
The specialized tags, developed by Woods Hole Oceanographic Institution in Woods Hole, Mass., record sound and movement data to help study how the animals behave during normal activities, such as diving to forage for food, and respond to sounds researchers introduced into the water. Data from this year's field work, which ended Oct. 2, are being processed. A preliminary report is scheduled to be completed in November.
"The hope for this year was basically to repeat what we accomplished last year and get several more samples, and also to use a slightly wider variety of signal types simulating various iterations of Navy sonar signals," said Dr. Brandon Southall, director of NOAA's Ocean Acoustics Program in Silver Spring, Md.
"We're trying to study what's going on with animal responses to these signals and what we can do to try and minimize the impact of active sonar on marine mammals, generally, and beaked whales, specifically," Southall added.
In addition to the tagging effort, which collected detailed information on individual whales, researchers used AUTEC's array of underwater hydrophones to detect and localize whales by passively listening to and analyzing the sounds they made.
"We've been using hydrophones to study their spatial and temporal distribution, as well as vocalizations before, during and after sonar operations," said David Moretti, an electrical engineer with the Naval Undersea Warfare Center in Newport, R.I.
Developed as part of the Marine Mammal Monitoring on Navy Ranges (M3R) program, Moretti said the Navy's capabilities for finding marine mammals were used to guide BRS researchers to whales during the study at AUTEC.
In 2007, the initial year of the BRS, 10 whales were tagged, and "play back" data were collected on three individuals, including a Blainville's beaked whale.
Beaked whales are extreme divers that have been recorded at depths in excess of 1,500 meters. Elusive and difficult-to-study, they are primarily known through stranding incidents, though Navy-funded research has begun to unlock more information on their basic biology and their responses to sound.
During last year's BRS, an individual female beaked whale appeared to respond to sonar sound by breaking off a foraging dive, rising to the surface earlier than expected, and cautiously surfacing well away from the sound source. Noting that further study is needed, Southall said initial results from two seasons of BRS, as well as related observations at AUTEC, indicate that beaked whales appear to have an avoidance response to simulated sonar sounds that may distinguish them from other marine mammals.
"These deep-diving beaked whales just seem to move away from these kinds of sounds, from our early observations," he said.
The study is part of the Navy's ongoing effort to understand the effects of man-made sound in the marine environment, particularly as it relates to active sonar, an anti-submarine warfare tool in which sound is introduced into the water to detect potential threats to Sailors.
"The Navy provides the range, funding and personnel for the BRS," said Jene Nissen, the environmental program acoustics manager at the Navy's U.S. Fleet Forces Command in Norfolk, Va. "We're concerned. We want to find an answer."
Sponsors of the study include Navy's Submarine Warfare Division, the Navy Environmental Readiness Division, the Office of Naval Research and the U.S. Department of Defense's Strategic Environmental Research and Development Program.
Navy officials have said the Navy is committed to both training realistically with active sonar and protecting the environment by minimizing potential impacts on marine life. The Navy has funded more than $100 million in marine mammal research over the past five years, including $26 million this past fiscal year, according to numbers compiled by the Office of the Assistant Secretary of the Navy, Installations and Environment.
"It's a hundred-percent commitment," said Dr. V. Frank Stone, marine resources program manager for the U.S. Navy Chief of Naval Operations, Environmental Readiness Division. "The Navy operates in the marine environment, and in a sense our Sailors are marine mammals. It is our responsibility and desire as environmental stewards to understand what the effects of our actions are and to do whatever is necessary to minimize those effects."
BRS study techniques built upon earlier work by many of the researchers, much of it funded by the Navy. The techniques used in the BRS have already informed recent scientific field work off the West Coast.
This summer, researchers tagged and tracked several whales during the 2008 Rim of the Pacific exercise that involved Navy sonar. According to Moretti, they currently are tracking a Cuvier's beaked whale and a fin whale tagged off the coast of California during an M3R test in August. The Navy and NOAA were among those funding and participating in the research.