If California sea lions continue their underwater buffet below Willamette Falls, they could push winter steelhead trout to the brink of extinction, state officials warned Monday.

Oregon Department of Fish and Wildlife highlighted the threat in a population feasibility study released Monday. Without federal intervention, they said, there's an 89 percent probability that least one population of the iconic fish species will go extinct in the near future.

"It's pretty dire," Shaun Clements, the agency's senior fish policy adviser said in an interview from a Clackamas County park just down river from the state's largest waterfall, where sea lions have been setting up shop around the time the trout try to make their trek to spawning grounds up river. "If we don't deal with this near-term risk, there might not be fish," he said.

The state's report comes as two Pacific Northwest congressional leaders are trying to give Oregon and Washington broader authority to kill sea lions at Bonneville Dam on the Columbia River. The bill would also apply to the sea lion logjam at Willamette Falls in Oregon City.

But the state's dire warning doesn't reflect the true scope of the problem, according to the Native Fish Society, a nonprofit advocacy group based in Oregon City.

Conrad Gowell, the nonprofit's river steward program director, said in a statement that the problems facing steelhead and chinook protected under the Endangered Species Act go far beyond sea lion predation. "River Stewards in the upper Willamette Basins have been calling on fisheries managers to shut down harvest on these ESA-listed fish, reform hatchery practices, restore access to historical habitat, and invest in solutions to the systemic problems of wild fish decline," he said. "Finger pointing at a singular cause is counter-productive to addressing the underlying problems and are just temporary and emergency measures."

For years, lawmakers have pushed for more latitude to intervene at Bonneville and prevent sea lions from snacking on spring Chinook salmon there. But state officials say the threat to steelhead on the Willamette River now poses a much greater risk.

In 2017, just 512 native steelhead made it past Willamette Falls on their journey to spawning grounds on the North and South Santiam, Molalla and Calapooia Rivers. That's the lowest winter steelhead run ever recorded, according to Clements.

In the early 2000s, the winter steelhead run was close to 15,000.

They believe sea lions have consumed one-quarter of the 2017 steelhead run.

If fewer than 100 fish make it past the falls for four consecutive years, a run will be deemed extinct.

The population study in Oregon incorporated fish counts dating back decades, and projected two scenarios over the next century: One with sea lions remaining on site and one with them gone.

Without sea lions, the risk of extinction was negligible, at just 6 percent. But if the marine mammals continued eating 25 percent of the run, the risk of extinction would rise to 89 percent.

According to Clements' analysis, the Willamette River populations have trended down while the Clackamas River's steelhead run rebounded.

The big difference? Sea lions.

In the past decade, sea lions have increasingly chosen to swim the 128 miles from the mouth of the Columbia River to the falls. Thousands congregate in Astoria for months at a time, but others swim up river for food.

According to an ODFW report, the state started monitoring sea lions at the falls in 1995. Through 2003, the population numbered fewer than one dozen. But the numbers soon ballooned, and in 2010, the state briefly started hazing the animals by shooting non-lethal rounds and other tactics. Today, Clements said, the population is around 40 animals when the sea lions swim up river.

Under the current exemption carved out under the 1974 Marine Mammal Protection Act, Oregon can legally kill up to 92 animals at Bonneville. In 2016, the states removed and euthanized 59 sea lions at Bonneville, the most in any single year since the program began in 2008 (two additional sea lions were accidentally killed).

Clements said Oregon recently filed a permit seeking the ability to kill sea lions at the Willamette Falls site for the first time.

The bill introduced by Reps. Jaime Herrera-Beutler, R-Washington, and Kurt Schrader, D-Oregon -- would allow removal of up to 920 sea lions at Willamette Falls or Bonneville.

Clements compared the Willamette Falls situation to Seattle's Ballard Locks, the manmade gateway to Lake Washington where sea lions were blamed for eliminating the native steelhead run there.

The Humane Society of The United States has said that killing sea lions is a distraction from more important projects such as addressing fish habitat and dams that prevent fish passage.

-- Andrew Theen

atheen@oregonian.com

503-294-4026

@andrewtheen