Federal marine regulators have approved a Navy plan and mitigation measures for using active sonar around Hawai'i during anti-submarine warfare training, just weeks before a two-year Pentagon exemption to the Marine Mammal Protection Act is scheduled to expire.

"Without that exemption in place, we need an authorization from (the National Marine Fisheries Service) to continue sonar training," said Mark Matsunaga, a spokesman for the Navy's U.S. Pacific Fleet.

The National Oceanic and Atmospheric Administration's Fisheries Service said in a release yesterday that the new measures "should minimize the potential for injury and death, and significantly reduce the number of marine mammals exposed to levels of sound likely to cause temporary loss of hearing."

Among the requirements, the Navy has to reduce mid-frequency sonar transmissions by 6 decibels when marine mammals are detected within 1,000 yards of a ship's underwater sonar dome during training.

Ships have to power down sonar by 10 decibels if animals are within 500 yards, and the sonar has to be shut down completely if marine mammals such as whales or dolphins are within 200 yards.

NOAA's Fisheries Service said it does not expect the sonar exercises to result in serious injury or death to marine mammals, but added that in a "small number of cases, exposure to sonar in certain circumstances has been associated with the stranding of some marine mammals, and some injury or death potentially could occur despite the best efforts of the Navy."

As a result, the authorization allows for "incidental impacts," including injury or death to up to 10 animals of each of 11 species over the five years covered by the new regulation.

The Natural Resources Defense Council, which has sued the Navy in the past over the use of sonar, could not be reached for comment late yesterday.

The Pentagon exemption to the Marine Mammal Protection Act was put in place in January of 2007 in the face of legal challenges to sonar. It expires on Jan. 23, officials said. The Navy has training ranges off Hawai'i, southern California and the East Coast.

NOAA Fisheries enforces the Marine Mammal Protection Act.

The Fisheries Service authorization for Hawai'i — published yesterday in the Federal Register — is the latest resolution of sonar issues for the Navy in a years-long battle with environmentalists, who claim that the underwater sound injures marine mammals.

The Navy and the Natural Resources Defense Council last month settled a lawsuit filed in 2005 challenging the Navy's environmental review before using mid-frequency sonar in training.

In November, the U.S. Supreme Court lifted sonar restrictions placed on the Navy in southern California, saying they were outweighed by the Navy's need to conduct realistic training.

Separately, a lawsuit filed in 2007 by the environmental group Earthjustice sought to stop sonar exercises off Hawai'i for carrier and amphibious strike groups heading to the western Pacific.

U.S. District Judge David Ezra ruled in Honolulu that the Navy had to follow a series of sonar mitigation steps. But the two-year period challenged by Earthjustice ends this month, and after that, the lawsuit will be moot.

Earthjustice attorney Paul Achitoff in Honolulu yesterday said he was still reviewing the NOAA Fisheries authorization.

"Whether we want to do anything legally is going to be a question of our analysis of these new documents," he said. "We accomplished what we intended to accomplish with the existing lawsuit — which was get the court to require the Navy to implement additional mitigation."

Ezra said in February 2008 that while the Navy disputed the factors associated with marine mammal strandings, "there is little disagreement that (mid-frequency active) sonar can cause injury, death and behavioral alteration to these animals."

The Navy said it previously put in place 29 of its own measures to protect whales from sonar. The USS Boxer amphibious strike group, which left San Diego on Friday, is expected to conduct anti-submarine warfare training off Hawai'i in coming days before heading to the Persian Gulf.