Experts say that's a problem for marine mammals and other aquatic animals. Sound is their primary means of learning about their environment, communicating, and navigating.
"Military sonar needlessly threatens whole populations of whales and other marine animals," said Joel Reynolds, an attorney for NRDC. "The Navy refuses to take basic precautions that could spare these majestic creatures."
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The Washington, D.C.-based nonprofit, along with several animal welfare and environmental groups, sued the Navy last week, citing harm to whales caused by mid-frequency sonar.
The technology is associated with strandingswhen marine animals swim or float onto shore and become beached or stuck in shallow water.
Whale strandings have occurred for decades for a variety of reasons.
In 2000 17 whales from three species beached themselves in the Bahamas after Navy ships conducted mid-range sonar exercises. Of those stranded, seven animals died.
A federal investigation concluded sonar was the most likely cause of the whales' stranding.
Adding to the controversy, the military's preferred training site in North Carolina is near an area where a mass whale stranding took place in January, not long after the Navy conducted sonar exercises in the region.
The National Marine Fisheries Service, a federal agency that protects marine mammals, is investigating the cause of the most recent stranding.
Donna Wieting of the Fisheries Service said the agency aimed to complete the investigation this summer but was delayed in part by Hurricanes Katrina and Rita. Results are expected in January 2006.
Brantley, the Navy spokesperson, said precautions would be taken to protect mammals at the newly proposed range. Steps would include training personnel to recognize marine species and conducting visual surveys before and during exercises.
If animals are seen within 350 yards (320 meters) of a vessel, he said, active sonar transmission levels would be reduced.
"Marine mammals would have to be very close to the sonar source to experience physical harm or injury," Brantley said.
Some experts believe sonar is a nonissue given the abundance of man-made noises filling the world's seas.
Power boats, oil tankers, offshore drilling, and seismic surveys all contribute to the acoustic traffic jam.
Arthur Popper co-directs the Center for Comparative and Evolutionary Biology of Hearing at the University of Maryland.
"The impact on fish or marine mammals from sonar is trivial compared to the sounds produced on a much more global scale by the general increase of human activity in the oceans," Popper said. "It's almost a phony issue."
The acoustic biologist recently studied the effect of low-frequency sonar on several fish species likely to be exposed to sound waves in their natural environment.
The result showed fish experienced short-term hearing loss, he said, but sustained no long-term damage.
The Navy funded Popper's study, but the scientist is quick to assert that he was not pressured by the military to produce favorable test results. He plans to publish the study sometime next year.
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