The Natural Resources Defense Council (NRDC), which had sued to block deployment of the new system, hailed it as "a ground-breaking accord," but the navy declined to comment until US Magistrate Elizabeth Laporte makes it official.

"Under the terms of the agreement, the navy will limit use of the new sonar system to specific areas along the eastern seaboard of Asia (around North Korea and China), including portions of the Sea of Japan, the East and South China Seas and the Philippine Sea," the NRDC said.

The navy agreed not to use the sonar system in waters off the Hawaiian islands, where it had been permitted to test and train with the system, and it also agreed to certain seasonal and coastal exclusions, the NRDC said.

The limits do not apply to times of war or heightened threat, it said.

The NRDC sued after the National Oceanic and Atmospheric Administration awarded the navy a permit in 2001 to deploy the system, which is designed to detect increasingly quiet diesel submarines over long distances.

Laporte, who was expected to act on the agreement later this week, issued a tailored injunction last year allowing the navy to train and test with the system while the two sides negotiated a permanent injunction.

"The navy is going to obey the law, whatever the decision may be. But any limits placed on the system does have impacts on readiness," said Lieutenant Commander Cappy Surette, a navy spokesman.

"This agreement safeguards both marine life and national security," said Joel Reynolds, the NRDC official who negotiated it. "It will prevent the needless injury, harassment and death of countless whales, porpoises and fish, and yet allow the navy to do what is necessary to defend our country."

The system, formally known as the Surveillance Towed Array Sensor System, emits low-frequency sounds in powerful bursts over hundreds of miles (kilometers) that environmentalists believe can be harmful to whales and other marine mammals.

Active medium-range sonar has been associated with mass strandings of whales in the Bahamas, Madeira and the Canary islands, the NRDC said.

A recent study published in the journal Nature by English and Spanish scientists found that intense, active sonar may kill certain marine mammals by forcing them to surface too quickly, giving them the "bends."

An earlier two-year study conducted for a navy environmental impact review concluded that the impact of the low-frequency radar on marine mammals was negligible, Surette said.

"Each and every time it has been used, there has been no impact on marine mammals," he said.

The Congress, meanwhile, is considering a Pentagon-supported amendment to the defense appropriations bill called the Range and Readiness Preservation Initiative that Surette said would clarify the legal definition of "harassment" of marine mammals.

The NRDC said exempting the navy from provisions of the existing Marine Mammal Protection and Endangered Species acts would allow the navy to test the sonar systems anywhere.

TERRA.WIRE