Los Angeles: The Navy must abide by limits on its sonar training off the Southern California coast because exercises could harm dozens of species of whales and dolphins, a federal appeals court ruled.

The 9th US Circuit Court of Appeals on Friday night rejected the Navy's appeal of restrictions that banned high-powered sonar within 12 nautical miles, or 22.2 kilometres, off the coast and set other limits that could affect Navy training exercises to begin this month.

Conservation groups that had sued to block the Navy's use of high-powered sonar said the decision was a victory.

"The court found that the Navy must be environmentally responsible when training with high intensity sonar", Joel Reynolds, director of the Marine Mammal Protection Project at the Natural Resources Defense Council, said in a statement.

The Navy has argued that additional restrictions would hamper its ability to train effectively.