The Navy said it will be taking a number of new steps aimed at buffering marine mammals from sonar during upcoming Rim of the Pacific exercises off Hawai'i.

Among the steps announced yesterday is the establishment of geographic restrictions around the Islands for active sonar transmission. Zones of exclusion will ring the islands 13 to 14 miles out to sea, starting at the point where water depth reaches about 600 to 700 feet.

Cmdr. Dean W. Leech, a lawyer with U.S. Pacific Fleet, said the Navy has been "aggressively engaged" with the National Oceanic and Atmospheric Administration's Fisheries Service for about a year and a half to develop protective measures.

"It's a very, very conservative approach," Leech said of the active sonar exclusion zones. "(NOAA Fisheries) are very concerned because some people believe that there are higher concentrations of marine mammals close to shore."

Also planned for the first time in Rimpac's 35-year history are requirements to reduce sonar output by 6 decibels if marine mammals are spotted within 1,100 yards of a ship, a 10 decibel reduction within 550 yards, and complete elimination of active sonar within 220 yards.

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 from NOAA Fisheries to "harass" marine mammals when it uses mid-frequency sonar in the war games.

More than 40 ships, six submarines, 160 aircraft and almost 19,000 military personnel are taking part in the biennial Rimpac — the largest naval exercise in the world — scheduled Monday through July 28.

The war games actually will begin on July 5, with the USS Abraham Lincoln aircraft carrier strike group the centerpiece of U.S. involvement.

Several Pacific rim nations along with the United Kingdom are participating, including Australia, Canada, Chile, Peru, Japan and South Korea

The measures are a compromise between tactical needs and increasing concern for the impact on marine animals of active sonar and the powerful sound "ping" put by ships hunting for submarines.

"We want to balance what we've got to do from the standpoint of military training and readiness and exercises with our commitment to environmental protection and safeguards," said Capt. Matt Brown, a U.S. Pacific Fleet spokesman.

The Navy said a marine mammal "harassment" permit from NOAA Fisheries is expected by early next week.

The operating concessions, still being fine-tuned, haven't been easy. The offshore antisubmarine warfare training has been a key feature of Hawai'i operations for years, and a good spot to practice "choke point" exercises.

Cmdr. Bruce Shaw, the antisubmarine warfare integration and planning officer for Pacific Fleet, said "submarines pose a threat because of their stealthiness and because they can hide very close to ships and not be detected."

"Diesel submarines — which is the coming trend — are even more difficult to find because they are very quiet," Shaw said. More than 140 foreign diesel subs operate in and around the Pacific.

A diesel sub attack in a constricted choke point like the Strait of Malacca, through which a lot of commerce flows, would have far-reaching effects, Brown said.

"The economic impact that would have, not only on the U.S., but Japan, Korea, China, East Asia, is just very considerable," he said.

Six diesel subs from South Korea, Australia and Japan are expected to take part in Rimpac war games.

NOAA Fisheries has agreed to exceptions to the sonar exclusion zones for Rimpac to allow for "a lot of activity" at the Pacific Missile Range Facility off Kaua'i, Leech said, and "choke point" training between Maui and the Big Island and two spots between Ni'ihau and Kaua'i.

Aerial, shore and ship surveillance would be conducted during the training for marine mammals, the Navy said.

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

The Navy estimated there will be 33,331 incidents of sonar exposure to marine mammals —some animals affected more than once — resulting in behavioral disturbance during Rimpac.

Two years ago, during Rimpac, a pod of about 200 deep-water melon-headed whales stranded in the shallow waters of Hanalei Bay, Kaua'i.

NOAA Fisheries said the cause may never be unequivocally determined, but sonar use during the war games was a "plausible, if not likely, contributing factor."

Reach William Cole at wcole@honoluluadvertiser.com.