More certain, the Navy said, the Shoup did not cause a deadly stampede of marine mammals onto seashores when the Everett-based destroyer used its sonar during routine training in Haro Strait in May.
"We did not cause a mass stranding," said Navy Rear Adm. Len Hering, commander of Navy Region Northwest.
Some marine mammal experts, however, said the report was inconclusive.
The report states that the noise emitted from the Shoup's sonar "could not be ruled out" as a contributing cause of the porpoise deaths.
For that reason, members of the community of scientists that track killer whales and other marine wildlife rejected the notion that the Navy should now be able to walk away from blame in the porpoise deaths.
"I'm absolutely certain that they caused virtually every whale, dolphin and porpoise in Haro Straight on the fifth of May distress to the point of panic," said Ken Balcomb, senior scientist at the Center for Whale Research in Friday Harbor.
"There is no doubt that there was a massive response," he said.
The porpoises washed ashore after the Everett-based destroyer used its mid-range tactical sonar during routine training in Haro Strait, between Vancouver Island and San Juan Island, on May 5.
Release of the National Marine Fisheries Service's report on the porpoise deaths has been highly anticipated.
The agency assembled a team of biologists, veterinary pathologists, veterinarians, research scientists and a neuroanatomist who conducted extensive examinations in late July of 11 of the porpoises found stranded.
In the report, scientists said five of the 11 porpoises suffered blunt force trauma and illness, but no cause of death could be determined for the other six porpoises.
No definitive signs of acoustic trauma could be found in any of the porpoises that were studied, though. Scientists also said the mammals had decomposed, and that acoustic trauma as a contributing factor in the death of the porpoises could not be ruled out.
Pete Schroeder, a marine mammal consultant for the National Marine Fisheries Service and the Navy, took issue with that statement in the 60-plus page report, a preliminary study that will undergo 30 days of peer review.
"That statement is going to be pinged on for 30 days until the final report comes out," he said. Although the porpoises had started to decompose, it mostly affected the body tissues of the porpoises.
No noise damage was found on those inner ears that were studied, he said.
Fleeing from the sounds of sonar could have caused the porpoises to die from stress, or by beaching themselves or smashing their heads on boats or rocks, said Fred Felleman, a board member of the Seattle-based Orca Conservancy.
A total of 16 porpoises reportedly washed ashore in the weeks before and after the Shoup's trip through Haro Strait. Necropsies were conducted on 11 of the animals.
"The report does not absolve the Navy of responsibility," Felleman said.
Whale watchers and others in Haro Strait reported seeing whales and other marine mammals quickly flee the area while the Shoup was using its sonar.
The Navy's Hering, though, said witness reports on what marine wildlife did during the Shoup incident vary, and so the visual accounts of what happened might not be entirely accurate.
The Navy's Pacific Fleet is expected to release its own report of the Shoup incident later this week. Navy officials said information from the National Marine Fisheries Service report will be included in the Navy's analysis.
The Shoup, the only Navy warship in Puget Sound that has mid-range tactical sonar, is currently on a training mission. The destroyer must get approval from Navy brass in the Pacific Fleet before it can use its sonar in Puget Sound.
Hering said it was vital for Shoup sonar operators to use Haro Strait for training.
"The operator has got to operate that sonar in an environment that is similar ... to places in the world where we are denied access," Hering said.
Reporter Brian Kelly: 425-339-3422 or email@example.com. Reporter Lukas Velush: 425-339-3449 or firstname.lastname@example.org.
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