The remaining six may also have been victims of the shooting spree, but some drifted away in the tide before state veterinarians could perform a post-mortem. Another couldn’t be X-rayed because it had been decapitated, and the heft of the body would have required a crane to haul the animal out of the water and into a facility where it could be more thoroughly examined.

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“It was definitely an intentional removal, a clean cut,” said Casey Mclean, a veterinary nurse and executive director of SR3, a Seattle nonprofit focused on marine mammals.

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Whoever is shooting the animals, which are protected under the federal Marine Mammal Protection Act, faces a stiff penalty if caught. Harming one can result in a fine of up to $28,520 and one year of imprisonment. The string of incidents is under investigation by the National Oceanic and Atmospheric Administration’s Fisheries’ Office of Law Enforcement.

But perpetrators — and there have been many — are rarely caught. More than 600 sea lions were shot on the West Coast between 1991 and 2016, according to data collected by various stranding networks, which show that the incidents are on the rise.

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The recent killings in Seattle are different in scope, said Mclean, who has helped the state wildlife agency perform some of the necropsies. Before 2018, Mclean said, one to four illegal sea lion shootings were typical for the area during the fall salmon runs, when fishing increases.

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“It’s a huge spike,” Mclean said of the dozen confirmed killings this year.

Just as the culprits remain unknown, so does their specific motive. But sea lions certainly have their enemies.

The animals, which can stretch nearly eight feet long and weigh up to 800 pounds, are unpopular for several reasons. Some people don’t like the way they crowd around beaches and fishing docks, and pretty much no one is fond of the scents they leave behind.

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But the problem in Puget Sound is probably linked to fish. California sea lions love salmon, and that’s fueled resentment among fishermen. Of the very few people who faced charges for shooting sea lions along the Pacific Coast between 1998 and 2017, all were fishermen.

“Sea lions are smart. They will always choose easy pickings, like fish trapped in a net or being reeled into a boat or stalled at the base of a dam, fish ladder, or mouth of a river,” said Robin Lindsey, lead investigator for the Seal Sitters Marine Mammal Stranding Network, a volunteer group that patrols the shorelines of West Seattle.

But climate change and dams on the rivers the salmon have long depended on for breeding have left far fewer fish to go around.

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Meanwhile, far more sea lions are plying the Pacific than in previous decades. Hunting, bounty programs, habitat loss and pollutants caused populations to plummet by the 1970s, when fewer than 90,000 California sea lions remained. That enactment of the Marine Mammal Protection Act in 1972 helped the animals’ population rebound to around 300,000 today.

“The sea lions are a real conservation success story,” said Michael Milstein, a public affairs officer with the National Oceanic and Atmospheric Administration. “Now the question is how do we live with them and balance their need for resources at the same time as our need for those same resources, as well as other wildlife and their needs?”

According to a study published last year, sea lions and their pinniped relatives now consume up to 625 metric tons of Chinook salmon in Puget Sound each year. That’s twice as much fish as the resident killer whale population consumes, and six times more than commercial and recreational fishermen harvest.

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“Those numbers are just amazing and damning,” said Tom Nelson, a fisherman and host of an ESPN radio show called the “Outdoor Line.” “All the habitat increases, all the hatcheries releases, it’s all going right down the gullet of these pinnipeds.”

But Nelson, who has a degree in fisheries biology from the University of Washington, acknowledged that sea lions and seals are not the sole culprits. Fish habitat has shrunk as cities are expanded, river valleys are developed and upstream forests are harvested.

“We have done everything we could as a society in the last century to virtually eradicate [salmon] from western Washington,” Nelson said.

It’s a complicated equation for the government, which is also tasked with recovering a Chinook salmon population that is considered threatened in Puget Sound. And like sea lions, the 70 or so southern resident killer whales in the area also depend on salmon. The dwindling fish supply is cited as a possible reason this population of orcas is nearing extinction.

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One way NOAA has attempted to strike a balance is through limited killing of sea lions at the Bonneville Dam, on the border of Washington and Oregon, and at Willamette Falls in Oregon.

“This is where the fish have to kind of come together to go up the fish ladders, and it makes them easy targets for the sea lions,” Milstein said.

It’s not simply open season on sea lions, and unauthorized shootings are not allowed. According to Milstein, wildlife managers must first demonstrate that an individual sea lion is consuming fish. And even then, they are only allowed to remove a limited number of the animals in the area.

“I do think that we need to implement a management plan on sea lion population levels immediately,” said Ryley Fee, a member of both the Puget Sound Anglers sportfishing group and the Puget Sound Partnership Salmon Recovery Council. “Our action can’t continue to be no action.”

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Fee called the recent killings the work of a vigilante and said they “cast a bad light on the situation.” On the other hand, he said, the attention to them might be positive, “because it teaches the uneducated masses that aren’t really well versed in all the facets of fisheries management about the pinniped problem.”

Both the U.S. Senate and the House of Representatives recently passed bills that would make it easier for states and Native American tribes to lethally remove sea lions. Subtle differences between these two bills must be rectified before a final version goes to President Trump, but that is expected to happen by year’s end.

Mclean said the recent shootings are especially frustrating because even if you approach the problem with the view of someone who wants more fish for people or orcas, a few dead sea lions won’t solve the problem. She said she also doesn’t like seeing animals suffer.

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“We believe we need more science before we can say the sea lion population needs management,” she said. “But if that is to happen, this is not the way that it should be handled.”

A previous version of this article incorrectly spelled the surname of the executive director of SR3. It is Mclean, not McClean.