Scientists likely will never know why more than 30 whales beached along North Carolina's Outer Banks last January, although some evidence indicates sonar wasn't the cause, said a report the Navy released Wednesday.

The National Oceanic and Atmospheric Association issued the final report from the National Marine Fisheries Service, which is a part of the NOAA.

On Jan. 15-16, 2005, 33 pilot whales stranded near Oregon Inlet; one minke whale in northern North Carolina, and two dwarf sperm whales near Cape Hatteras, the fisheries service said.

While the research eliminated several causes for the beaching that would implicate sonar, the report concluded: "On the basis of examination of physical evidence in the affected whales, however, we cannot definitively conclude that there was or was not a causal link between anthropogenic sonar activity or environmental conditions [or a combination of those factors] and the strandings."

The report said fisheries services investigators did not find common injuries that would indicate a single cause for the beaching, such as sonar.

They also did not find gas emboli lesions, or bubbles similar to "the bends," that have been associated with past sonar-related strandings, the report said.

Rear Adm. James Symonds, director of the Navy's environmental programs, said the Navy believes its sonar operations could not be responsible because they occurred two to three days before the stranding and more than 50 nautical miles from Oregon Inlet.

"The NOAA report clearly acknowledges that there is no pathology implicating sonar as a cause of the stranding," Symonds said.

The minke whale was emaciated and was likely a dependent calf that became separated from the female, the report said, adding that its stranding was probably coincidental.

Three pilot whales and one dwarf sperm showed signs of chronic debilitation that could have contributed to the stranding, the report said.

One pilot whale had a subdural hemorrhage that could have been present from the stranding or that the stranding could have caused.

Because of the previous sonar activity in the area, "the association between the naval sonar activity and the location and timing of the event could be a causal rather than a coincidental relationship," the report said.

"However, evidence supporting a definitive association is lacking, and, in particular, there are differences in operational/environmental characteristics between this event and previous events where sonar has apparently played a role in marine mammal strandings. This does not preclude behavioral avoidance of noise exposure."

But some environmental conditions, including strong winds, are similar to other mass strandings, the report said.

The Navy uses sonar technology, which bounces sound waves off underwater objects to map the geography underwater, to detect threats and navigate. But sound waves also are suspected of hurting whales, possibly by damaging their hearing or causing them to rise to the surface too quickly and get the bends.

The issue is an especially sensitive one in North Carolina, where the Navy wants to build a 661-square-mile sonar range off the state's coast over 10 years at an estimated cost of $98 million. It would be used to train sailors and pilots to track submarines.