An environmental group is pointing a finger at sonar and the Navy's Rim of the Pacific exercises in the stranding and death of a 15-foot Cuvier's beaked whale Monday on Moloka'i, but the National Marine Fisheries Service said it doesn't yet know what caused the juvenile male animal to enter the shallow water.

U.S. Pacific Fleet spokesman Mark Matsunaga, meanwhile, said it's "premature, speculative and irresponsible to link naval activities to this stranding."

A veterinarian who examined the 2,500-pound deep-diving whale, which stranded itself at least twice, determined it was sick and would not recover, said Chris Yates, who heads the protected resources division of the National Oceanic and Atmospheric Administration's Fisheries Service here.

Officials were made aware of the stranding at 8:30 a.m. Monday, and Yates said the decision was made to euthanize the whale at about 4:30 p.m.

"The animal was sick, would obviously have not lived being pushed out on its own, and would have suffered more," Yates said.

A Moloka'i public works crew transported the whale to the airport, and the Coast Guard flew it in a C-130 aircraft to Honolulu. A necropsy still was being conducted yesterday at Hawai'i Pacific University.

"Obviously, we want to do this as quick as we can," Yates said. "They could call me up and say, 'Oh, gosh, look what we found. This animal had some major problem.' " On the other hand, a cause of death may not be found, he said.

The environmental law firm Earthjustice said the stranding came as the Navy conducted its multinational Rimpac exercise in Hawai'i waters.

Ten nations, 35 ships, including the aircraft carrier Kitty Hawk, six submarines, 150 aircraft and 20,000 military personnel participated in the monthlong Rimpac which had a heavy focus on sonar use for anti-submarine warfare training.

"Deep-diving whales have come into the international spotlight as mass strandings around the world have regularly been linked to naval mid-frequency active sonar use," Earthjustice said.

NOAA Fisheries determined that the use of midfrequency Navy sonar was a "plausible, if not likely" contributing factor to the mass stranding of up to 200 melon-headed whales in Hanalei Bay, Kaua'i, during Rimpac naval exercises in 2004.

One contributor to the finding, Brandon Southall, later said the report did not conclude that Navy sonar caused the stranding. "We do not know what caused it," Southall said.

Earthjustice and the Natural Resources Defense Council have sued the Navy multiple times over active sonar use.

Yates said officials have no idea why the beaked whale stranded itself, but acknowledged that noise can be an issue for marine mammals.

"They hear just like we do," he said. "But on the other side of that, we also want to make very clear that marine mammals strand all the time for various reasons, and it would really be unfortunate and premature to jump to conclusions about the cause of the stranding when we really don't have any idea."

Yates said there are typically about two dozen strandings a year in Hawai'i. Monday's was the eighth whale or dolphin stranding of 2008. A past estimate placed the number of Cuvier's beaked whales around the Hawaiian Islands at more than 12,000.

There had been five Cuvier's beaked whale strandings reported in Hawai'i before Monday, in 1950, 1970, 1981, 1996 and 1998, NOAA Fisheries said.

The Navy said it conducted a 10-nautical mile search yesterday by air for other possible strandings, but none was seen. During Rimpac, NOAA Fisheries researchers tagged some marine mammals to see how they reacted to the naval maneuvers.