And Scientists worry it might be fallout from a Navy sonar test.

Orcas reacted frantically when a Navy destroyer tested its sonar last week off San Juan Island. Whale watchers worry the sonar confused, even hurt the whales.

And now there's a new worry.

Researchers in Friday Harbor want to know if the sonar is behind the deaths of five Harbor porpoises.

They pulled three of them from the water in San Juan County. A local veterinarian will do necropsies next week - looking for signs of trauma.

Rowann Tallmon is a stranding expert with the Friday Harbor Whale Museum. She explains what the vet will look for: "Of special concern, because of the sonar testing, is taking a look at the ears and seeing if there's any bleeding in the ears or evidence of bleeding before it died," Tallmon says.

The sonar recordings were taken on May 5. Several of the dead porpoises were pulled from the water before that date.

But whale researchers say they heard similar sonar tests in April -- even as far back as December and January.

Researchers worry that because the noise could be loud enough to kill, or at the very least, it's disruptive.

"Harbor Porpoises especially are getting chased out of areas that have a lot of high boat traffic," Tallmon said. "They've very shy around boats and so we don't see as many of them around here as we used to. So that's a concern."

It's not unusual for a handful of porpoises to turn up dead this time of year. But this is the first time Friday Harbor researchers will examine each animal, hoping to find out why they're dying.

"Yeah, it's a mystery at this point," Tallmon said.

The Friday Harbor researchers will turn their data over to the National Marine Fisheries Service. If there's a connection to Navy sonar, it will be up to the federal scientists to talk to the Defense Department.