A Navy-sponsored study on the behavioral response of toothed whales to various sounds in the ocean has provided fresh insights into these little-understood mammals.
Of particular interest to the Navy is the whales' reaction to the sound of mid-frequency active sonar, an issue that has stirred some controversy and resulted in five lawsuits against Navy training practices.
"Our goal was to develop and safely test responses of whales to sound, particularly beaked whales, which we know seem to be more affected by mid-frequency active sonar than other species," said Navy Rear Adm. Lawrence S. Rice, director of the Chief of Naval Operations Environmental Readiness Division, during an interview on Pentagon Web Radio's "Armed with Science: Research and Applications for the Modern Military" audio webcast, April 22.
Rice said the focus on beaked whales is due to several incidents in which groups of beaked whales stranded themselves near naval exercises using mid-frequency sonar. The first such incident to attract national attention was in the Bahamas in 2000, when 17 whales stranded themselves. In the ensuing debate, sonar frequently has been depicted by concerned citizens and media reports as injurious to all whales.
The admiral pointed out, however, that sonar exercises on the Navy's Atlantic Undersea Test and Evaluation Center range, 40 miles south of the site of the Bahamas stranding location, consistently are conducted in the presence of a resident population of beaked whales, apparently without negative effects.
"There's a lot of scientific uncertainty regarding the conditions that lead to these strandings," said Rice, noting that whales do not beach themselves every time active sonar is turned on.
For the Navy, the problem is not purely academic. Multi-million-dollar training exercises, which the Navy maintains are critical for national defense, have been hampered by lawsuits. Rice said a lack of verifiable knowledge in this area means the debate is not informed by science and that proposed restrictions on training are based primarily on conjecture.
The behavioral response study is designed to expand understanding of whale response to acoustic sound, Rice said. Although sponsored in part by the Navy, the study is conducted under the auspices of the National Marine Fisheries Service, with participation by scientists and engineers from some of the top research organizations, including Woods Hole Oceanographic Institution, Scripps Institute of Oceanography, Duke University, University of North Carolina at Wilmington, and the Scottish Oceans Institute at the University of St. Andrews.
The study, the first of its kind, began in 2007. Rice said it has been conducted at the Navy's AUTEC range because the area has listening devices mounted on the sea floor that can monitor the movement of marine mammals and because of the range's resident population of beaked whales.
The study began by attaching digital recording tags to the whales with suction cups and following their dive patterns. Researchers then introduced sound into the water and observed changes in the whales' behavior. The sounds included synthesized mid-frequency sonar pings, the call of a predatory killer whale and random sound samples.
Initial results showed that all three sounds caused the beaked whales to slow their ascent to the surface and to move deliberately away from the sound source, but in none of the cases did they seem panicked, Rice said.
The researchers also tagged a pilot whale, a melon-headed whale and a false killer whale and exposed them to the same sound sources. They didn't seem to respond to the sounds, Rice said.
"Their dive profiles look almost exactly the same whether they're receiving sound or not," the admiral said. "And again, that was above 150 decibels. They were just kind of milling around out there."
Rice said forthcoming research will be conducted this year in the Mediterranean Sea with beaked whale stocks that are not as routinely exposed to sonar as those in the AUTEC.
"Everyone agrees," the admiral said, "that the best available science, frankly, isn't really good. Unfortunately, it's all we have right now, and we're hoping that the results of the [behavioral response study] will plug into this."