An examination on harbor porpoises that were found washed ashore in Puget Sound last year did not appear to have acoustic damage from the USS Shoup’s sonar, Navy officials said Monday.
“The only definitive cause of death to the porpoises was either blunt trauma or illness,” the Navy said in a statement.
More than a dozen porpoises reportedly washed ashore after the Everett-based destroyer USS Shoup used its mid-range tactical sonar in Haro Strait, between Vancouver Island and San Juan Island, on May 5.
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 will release its final report on the Shoup incident in the near future, after information from the necropsies has been folded into the report.
The National Marine Fisheries Service released its report on the porpoises Monday. Eleven porpoises were examined by the agency after the mammals washed ashore.
The agency assembled a team of biologists, veterinary pathologists, veterinarians, research scientists and a neuroanatomist who conducted extensive examinations of the porpoises in late July.
In the report, scientists said five of the 11 porpoises had suffered from blunt force trauma, 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, however. But 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.
“The multi-disciplinary team noted that lesions consistent with acoustic trauma can be difficult to interpret or obscured, especially in animals in advanced post-mortem decomposition,” the report said.
Marine mammal experts that had pressed for necropsies of the stranded porpoises said they hadn’t yet reviewed the report, but said some of the porpoises that were brought in weren’t badly decomposed.
“The ones we picked up on Whidbey Island weren’t decomposed at all. They were very fresh. They were picked up very quickly,” said Susan Berta, spokeswoman for the Orca Network, a nonprofit education organization and a member of the Island County marine mammal stranding network.
The network picked up two of the porpoises that were studied by fisheries scientists.
Berta said the Orca Network would be reviewing the report.
Navy Rear Adm. Len Hering, commander of Navy Region Northwest, was scheduled to speak with reporters later today about the report.
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