A federal appeals court ordered the U.S. Navy to mitigate any harm its sonar exercises do to marine animals.
The ruling means the navy must find ways to lessen the harm its sonar exercises do to whales and other marine life off the coast of southern California.
A three-judge panel from the 9th Circuit U.S. Court of Appeals allowed the navy to continue its current round of exercises through Nov. 22, but barred it from performing more tests until a federal district court helped it figure out how to perform the tests in a less harmful manner.
Environmentalists, led by the National Resources Defense Council (NRDC), claim that the mid-frequency sonar used by the navy during its exercises harms marine life.
Los Angeles-based U.S. District Judge Florence-Marie Cooper ruled on Aug. 7 in the NRDC's favor, ordering a preliminary injunction banning all such tests. However, the majority on a three-judge panel ruled on Aug. 31 that national security outweighed environmental concerns.
"The safety of our whales must be weighed, and so must the safety of our warriors. And our country," Judge Andrew Kleinfeld wrote for the majority.
But Tuesday's ruling said that "plaintiffs have shown a strong likelihood of success on the merits of their claims."
However, the panel also ruled that a blanket prohibition of all such exercises was too broad.
Environmentalists have supported the decision.