(Adds details on ruling, background, comment from Navy)
By Laura Zuckerman
Sept 26 (Reuters) - A federal judge in California has sided with environmental groups in their lawsuit against the U.S. government over Navy training exercises off the West Coast involving sonar that they say harms endangered whales, dolphins and other protected marine mammals.
The ruling in a long-running dispute pitting whales against the military requires federal biologists to reconsider permits allowing the Navy to potentially kill or disrupt marine mammals while conducting anti-submarine warfare exercises off the Pacific Northwest.
In a 43-page opinion issued late on Wednesday, U.S. Magistrate Nandor Vadas in Eureka, California, found that the National Marine Fisheries Service failed to apply the best available science in assessing impacts on whales and dolphins from the Navy's use of sonar.
Environmental groups said similar mid-frequency sonar by the Navy has been linked to fatal mass strandings of marine mammals around the world, including Hawaii, the Bahamas, Greece, the Canary Islands and Spain.
High-intensity noise from sonar - pulses of sound emitted to pinpoint underwater objects at a distance through the echo they produce - can also disrupt marine mammals' migration, nursing, breeding and feeding, the plaintiffs argued.
Conservationists have said the technology can be especially disturbing for creatures such as whales and dolphins that use a natural form of bio-sonar, called echolocation, to hunt for prey, detect predators and communicate with each other.
Under the judge's decision, the Marine Fisheries Service must reassess its permits to the Navy based on new research showing that marine mammals are far more sensitive to sonar and other underwater noises than previously believed.
Those assessments could trigger a requirement that the Navy do more to protect whales and dolphins in the training grounds in question, which stretch from northern California to the Canadian border.
The Navy says its sonar exercises in that region are confined mainly to open waters off the northern coast of Washington state, and that such operations are conducted by just one warship for no more than 90 minutes at a time. The Navy also conducts anti-sub training with sonar-emitting buoys dropped into the sea by aircraft.
The intermittent pulses, or pings, in sonar training are typically emitted at the rate of one every half minute, with each ping lasting about a second, according to the court ruling.
A spokeswoman for the Marine Fisheries Service, a branch of the National Oceanic and Atmospheric Administration, said the agency was reviewing the decision.
The Navy said it was studying the ruling and noted it was not a party to the litigation, but otherwise declined comment, except to say it was "committed to complying with environmental laws and protecting the environment."
Environmentalists hailed the ruling as a key victory.
"Today's ruling gives whales and other marine mammals a fighting chance against the Navy," said Miyoko Sakashita, oceans director at the Center for Biological Diversity. "This ruling means that the Navy must take greater precautions to protect marine life."
The ruling does not order an immediate halt to any Navy training exercises. Instead, it requires the NOAA to re-evaluate the Navy permits under the terms of the Endangered Species Act and Marine Mammal Protection Act.
The judge gave the agency 20 days to file a court brief suggesting how long it should take to conduct the permit review and how the scope of the reassessment should be defined.
In 2008, the U.S. Supreme Court sided with the Navy in a similar case, ruling that sonar training exercises off the Southern California coast could be conducted without restrictions designed to safeguard marine life. (Reporting by Laura Zuckerman in Salmon, Idaho; Additional reporting by David Alexander in Washington; Editing by Steve Gorman, Bob Burgdorfer and Lisa Shumaker)