At least 37 whales beached themselves and died along the North Carolina shore earlier this month soon after Navy vessels on a deep-water training mission off the coast used powerful sonar as part of the exercise.
Although the Navy says any connection between the strandings and its active sonar is "unlikely" -- because the underwater detection system was used more than 200 miles from where the whales beached themselves -- it is cooperating with other federal agencies probing a possible link. Government fisheries officials, as well as activists for whales, say the fact that three species of whales died in the incident suggests that sonar may have been the cause.
National Oceanic and Atmospheric Administration scientists "are looking at all the possible causes of this stranding, which was a significant one," spokeswoman Connie Barclay said. Although the number of whales that came ashore is far from a record for mass strandings, Barclay said that "it's very curious to have three different kinds of whales strand, and a number of possible causes are being examined. Sonar is certainly one of them."
The possible connection between naval sonar and the deaths of whales and other marine mammals has become an increasingly controversial issue since the Navy acknowledged that the loud blasts of its sonar helped cause a mass stranding of whales in the Bahamas in 2000. Since then, critics have accused the Navy of involvement in numerous mass strandings in U.S. and international waters, and federal environmental officials have concluded in some instances that the loud pulses from active sonar cannot be ruled out as a cause.
The North Carolina strandings could be especially problematic for the Navy because it hopes to establish a 500-square-nautical-mile underwater sonar testing range off that coast. The Navy says a draft environmental impact statement is near completion, and officials have said the range is a high priority.
Most of the animals that died in the latest incident were pilot whales, which stranded around the Oregon Inlet of the Outer Banks on Jan. 15. One newborn minke whale also beached at Corolla that day, and two dwarf sperm whales came ashore at Buxton on Jan. 16, locations about 60 miles north and south of the inlet. Six of the pilot whales were pregnant when they died, Barclay said.
None of the three whale species is considered endangered, though NOAA officials say their populations are relatively small and little understood in the Atlantic. But other endangered marine animals -- including right and humpback whales and numerous species of sea turtles -- regularly migrate through the waters off North Carolina.
Navy officials said that the USS Kearsarge Expeditionary Strike Group, based in Norfolk, was conducting an anti-submarine exercise about 240 nautical miles from the Oregon Inlet on Jan. 14 and 15.
In e-mailed answers to questions, the Navy said a review of activities after following the strandings concluded that "no Navy ships were using active sonar within 50 nautical miles radius" of the inlet on Jan. 15 or the four days preceding -- although one ship not associated with the strike group did use sonar for seven minutes about 90 nautical miles south-southeast of Oregon Inlet. The strike group was on its way to a deployment after the training exercise, the Navy said.
Sonar acts as the underwater eyes and ears of the Navy, and intermittent bursts are often used in transit to detect potential enemies and other dangers. In addition, Navy officials increasingly believe that inexpensive quiet submarines from hostile nations pose a potential threat and want to upgrade sonar tracking systems to protect against intrusions into U.S. coastal waters. The Navy now uses mid-frequency sonar for its tracking but wants to deploy a new generation of low-frequency sonar that travels much farther underwater and is more powerful.
The Navy has sometimes been slow to acknowledge that its ships were in an area where strandings occurred and has accepted responsibility only in the Bahamas event. Environmental activists said that track record makes them skeptical of the Navy's statements about the North Carolina strandings.
"The circumstances are troubling," said Michael Jasny, a lawyer for the Natural Resources Defense Council, which has sued the Navy on other sonar-related issues. "After so many whale deaths caused by sonar, these latest strandings are a red flag. . . . Unfortunately, the Navy has a long history of denial."
The Outer Banks area is close to the Norfolk base and on the general course to where the exercises were held.
Most of the stranded whales were dead when they were found, and NOAA scientists are conducting necropsies of many of the animals to try to determine a cause of death. Although pilot whales travel in herds and are prone to strandings, the other two whale species are not, officials said.
Pilot and dwarf sperm whales are both deep-diving animals that feed off the ocean floor and slopes of the continental shelf. The other whale strandings linked to sonar use have also involved deep-diving species, such as the beaked whale. Researchers have theorized that the loud sounds of sonar can damage the whales' sensitive hearing system and cause them to surface too quickly from fright. After another stranding off the Canary Islands in 2002, researchers found unusual gas bubbles in some whale organs -- leading them to conclude that the animals suffered from a form of decompression sickness similar to the bends.
The Navy's plan for an East Coast underwater sonar testing range was first announced in 1996. Since then, the plan has been discussed internally and work on an environmental impact statement has proceeded, with some input from NOAA.
A Navy spokesman said last year that a final decision had not been made on where to locate the test site. But in April, the Atlantic Division of the Naval Facilities Engineering Command said in a statement: "The Navy's preferred site for the range is in the Cherry Point Operating Area located in Onslow Bay, southeast of New River, North Carolina, and approximately 105 km (57 nautical miles) from the North Carolina shoreline."