The U.S. navy said Saturday a deal reached with the Natural Resources Defence Council and other groups requires it to continue to research how sonar affects whales and other marine mammals, but doesn't require sailors to adopt additional measures to protect the animals when they use sonar.
The agreement comes one month after the U.S. Supreme Court ruled in favour of the navy in another sonar lawsuit the NRDC filed.
"The navy is pleased that after more than three years of extensive litigation, this matter has been brought to an end on favourable terms," Frank R. Jimenez, the navy's general counsel, said in a statement.
NRDC officials could not immediately be reached for comment. The plaintiffs asked the judge to dismiss the case on Friday.
The NRDC and five other plaintiffs filed the lawsuit in Federal Court in the Central District of California on Oct. 19, 2005.
The complaint sought a court order to curb the use of mid-frequency sonar, the navy's preferred method for detecting enemy submarines, on the grounds the sonar disturbs and sometimes kills whales and dolphins.
The navy said the suit was amended twice so that it challenged its use of sonar in 370 specific training and testing activities around the world.
In the years since, federal courts in California and Hawaii ruled in favor of the NRDC and other environmental groups and ordered the navy to restrict its use of sonar to protect the animals.
Supreme Court rules in favour of navy
But last month, in a ruling on an NRDC lawsuit challenging the navy's sonar training exercises off Southern California, the Supreme Court ruled that military training trumps protecting whales.
Chief Justice Roberts wrote that forcing the navy to deploy an inadequately trained anti-submarine fleet would jeopardize the safety of the fleet. He also wrote it was unclear how many marine mammals the navy's sonar exercises might harm.
The navy uses mid-frequency active sonar to send sound pulses through the water. Sailors listen for sound bouncing from objects to identify if enemy submarines are lurking nearby.
This technology is different from passive sonar, which sailors use to listen for the sounds enemy submarines emit themselves.
Environmentalists argue that mid-frequency active sonar can disrupt the feeding patterns of whales, and in the most extreme cases can kill whales by causing them to beach themselves.
But scientists aren't sure why sonar affects some species more than others. They also don't fully know how it hurts whales.
The navy acknowledges sonar may harm marine mammals but says it takes steps to protect whales. It says more research needs to be done to better understand how sonar affects whales before it adopts additional protective measures.
The Pacific Fleet has made anti-submarine warfare a top priority as more countries, including North Korea, Iran, and China, have been acquiring quiet diesel-electric submarines that are increasingly difficult to track.
The navy said the settlement, which was reached Friday, calls on it to spend $14.75 million US over three years on marine mammal research topics of interest to both the navy and the plaintiffs.
The navy said the long-range research program it adopted under the settlement is basically the same as the one it set out to follow in August 2005, two months before the lawsuit was filed.
Other plaintiffs were: International Fund for Animal Welfare, Cetacean Society International, League for Coastal Protection, Ocean Futures Society and Jean-Michel Cousteau.