The Navy plans to monitor more of the ocean around Hawai'i for sonar's possible adverse effects on marine mammals during this summer's Rim of the Pacific exercise.

Responding to scientific evidence that sonar can disrupt, injure or kill whales, dolphins and other sea creatures, the Navy for the first time is seeking a federal permit to "harass" marine mammals when it uses mid-frequency sonar in the war games.

As part of the proposal, the Navy would track the effects on marine mammals where the sonar intensity is at 173 decibels.

The Navy had wanted to monitor at 190 decibels, which would have encompassed a smaller area, but made the change because of pressure from the National Oceanic & Atmospheric Administration's Fisheries Service.

Because a greater area will be monitored, the proposal means that far more marine life is expected to be counted as being affected.

The Navy estimates there will be 33,331 incidents of sonar exposure to marine mammals —some animals affected more than once — resulting in behavioral disturbance during the multination naval exercise scheduled for June 26 to about July 28.

Two years ago, during Rimpac exercises, a pod of about 200 deep-water melon-headed whales congregated in the shallow waters of Hanalei Bay, Kaua'i. The gathering was unusual, and the results of an investigation into the cause are due out today.

The application made by the Navy to NOAA Fisheries for the "incidental harassment" of marine mammals — the first in Rimpac's 38-year history — is a result of environmental group pressure and emerging science, and could set a precedent for restrictions on future Navy anti-submarine warfare training elsewhere.

The biennial war games off Hawai'i are expected to include an aircraft carrier and participation by eight other nations in ship maneuvers, amphibious landings, gunfire and missile exercises, ship sinkings and — with the greatest use of active sonar — anti-submarine warfare.

"For Rimpac '06, the Navy incorporated emergent science into the reassessment of the effects (of) mid-frequency active sonar use," said Lt. Cmdr. Christy Hagen, a spokeswoman for U.S. Pacific Fleet.

For much the same reasons, the Navy previously did not seek what are called "incidental take" authorizations from NOAA Fisheries Service, as required by the Marine Mammal Protection Act.

There was, and still is, debate as to what impact sonar has on undersea animals, and what constitutes marine harassment.

"It gets back to the fact that the science is evolving, and based on that evolving science, we feel we're able to assess at this point what we may not have been able to assess previously," Hagen said.

Michael Jasny, an attorney for the Natural Resources Defense Council working out of Los Angeles, said the decision to lower the noise level at which marine animals are considered to be negatively affected — a provision required by NOAA Fisheries — is "absolutely an improvement."

The Navy's decision to seek federal approval for the mid-frequency sonar harassment of marine animals is long overdue, he said. "It took years and years and lots of public pressure to bring the Navy to the conclusion that it has to adhere to the law like everybody else," Jasny said.

In October, the Defense Council, a national nonprofit environmental organization, sued the Navy, saying, "there is no dispute that the Navy's use of mid-frequency active sonar can kill, injure and disturb many species, including marine mammals."

Among the council's complaints was that the Navy regularly failed to comply with federal environmental law, including its failure to obtain the "incidental harassment authorizations," as required by the Marine Mammal Protection Act.

The council said some mid-frequency sonar systems produce 235 decibels, as loud as a Saturn V rocket at launch. A supertanker generates 190 decibels.

Evidence of sonar-related harm first began to surface in March 2000, when 17 whales of four species stranded themselves on beaches in the Bahamas after a U.S. naval ships used active sonar, the council said.

A study published in 2003 in the journal Nature found that high-powered Navy sonar may give whales and other marine mammals a form of the bends, or decompression sickness, with bubbles forming in organ tissue.

In 2004, Congress defined "Level B" harassment of marine animals, which the Navy now has started to use for exercises like Rimpac, as "any act that disturbs or is likely to disturb" marine mammals in the wild.

For both an East Coast sonar training range proposal and Rimpac, the Navy set the threshold for "Level B" harassment — meaning behavioral disturbance without physical effects — at 190 decibels. But NOAA Fisheries countered that 173 decibels more accurately reflects the harassment threshold, and the Navy agreed to use that level for Rimpac.

With 190 decibels as the benchmark, the Navy previously predicted just 289 marine animal exposures for 532 hours of sonar operation during 44 anti-submarine exercises.

The Navy's Rimpac proposal includes protective measures.

"Our scientists believe these measures, if fully implemented, will avoid the potential for serious injury or mortality to marine mammals," said Dr. Bill Hogarth, director of NOAA Fisheries. "These mitigation measures will significantly reduce the number of marine mammals exposed to levels of sound likely to cause a behavioral disruption."

Donna Wieting, deputy director of the Office of Protected Resources for NOAA, said those preventive measures include the requirement that when marine mammals are detected within 1,000 meters of the sonar, a ship will limit transmission levels to at least 6 decibels below normal operating levels.

Within 500 meters, sonar would be limited to 10 decibels below typical operation, and within 200 meters, it would be turned off.

Hagen said for every 3 decibel source reduction, received energy drops by about 50 percent.

The Natural Resources Defense Council's Jasny said mitigation still is "inadequate to the task."

"The area that the Navy will be monitoring around ships is small compared to the area of impact," he said.

The Navy's Hagen, however, said "we (the Navy) operate in the ocean and we want to take care of it, and we continuously have to balance what we need to to do to protect the country and protect the environment."

Reach William Cole at wcole@honoluluadvertiser.com.