Puget Sound mystery: Series of sea lion shootings near Seattle prompts worries of landlubber safety Federal agents are probing the gunshot deaths of six sea lions near Seattle.

A series of mysterious fatal shootings of California sea lions that washed up on shore in a heavily populated area of Seattle have federal authorities concerned not only the mammals but for residents living near the Puget Sound, officials said.

Of the 16 sea lions that have been found dead in King and Kitsap Counties of Washington state, bullet wounds have been discovered in at least six of the carcasses, according to Seal Sitters Marine Mammal Stranding Network.

"Some of the animals have been found in the area of West Seattle, which is obviously a pretty populated area. So that's concerning both from the standpoint of the animals and public safety," Michael Milstein, West Coast region spokesman for the National Oceanic and Atmospheric Administration Fisheries, told ABC News.

He said NOAA investigators have been probing the fatal shootings since late September when the first in the spate of Northwest sea lion shootings was reported.

Milstein said the hunt for the killer or killers has yet to identify any suspects.

He also said some of the other dead sea lions discovered on shore could have suffered a similar fate.

"Six have been confirmed shot through physical exams or X-rays to find bullet fragments. But some animals are so deteriorated that you can't tell a whole lot," Milstein said.

Killing a sea lion is a federal crime under the U.S. Marine Mammal Protection Act, which was passed in 1972.

While Milstein couldn't definitively say why the sea lions are being targeted, he said investigators have a hunch.

"I can't really speculate on what was going through somebody's mind. Certainly, there has been tension about the sea lions basically pursuing some of the same prey that we do in terms of fisheries," Milstein said.

Earlier this month, Jon Nichols, the captain of an Alaskan fishing boat dubbed the Iron Hide, was sentenced to a month of home incarceration, 40 hours of community service and fined $5,000 after pleading guilty to charges of shooting and killing Steller sea lions with shotguns during the 2015 salmon fishing season. Nichols was also sentenced to five years probation and ordered to write an apology to be published in a national magazine.

Theodore Turgeon, 21, a deckhand on Nichols' boat, also pleaded guilty to shooting sea lions and was sentenced to home confinement and fined $5,000, according to the Department of Justice.

"The shootings were carried out using a pair of shotguns kept aboard the vessel, one each belonging to Nichols and Turgeon," the Department of Justice said in a statement. "Nichols would shoot the Steller sea lions himself, and at other times, [he] would drive the Iron Hide in the direction of the Steller sea lions to allow Turgeon and his crew to get a better shot."

Milstein said it's not unusual to find sea lions shot dead in the Northwest this time of the year and noted that most of the carcasses are males that likely swam up from sea lion breeding grounds in the Channel Islands off Southern California.

"This is the time of year when they're appearing in the Northwest and other places in larger numbers. They're out looking for food," Milstein said.