Correction: Incorrect data was included in a previous version of this story.
Decadeslong efforts by state and tribal agencies have slowly curbed sea lion populations in the region, yet officials still consider the pinnipeds a threat to at-risk salmon populations in the Columbia River.
Between August 2021 and May 2022, officials estimate 7,329 fish — 6,170 of which were salmon — in the Bonneville Dam tailrace were killed by Columbia River sea lions, according to the Portland U.S. Army Corps of Engineers’ 2022 predation report.
Dozens of sea lions congregate at the dam in the fall, winter and spring. They feast on chinook, steelhead and coho salmon, as well as sturgeon and other fish. Spring chinook salmon were disproportionately affected in the total amount of estimated fish that were killed.
Predation samples vary depending on the dam’s tailraces and seasons studied, leading the report to note that total predation at the Bonneville Dam may be higher than its estimates.
Both California and Steller sea lions are among the many culprits slowing salmon recovery. California sea lion populations have fallen, while Steller sea lions’ presence remains high, resulting in the latter presenting a continued risk to sturgeon and winter steelhead.
Kyle Tidwell, U.S. Army Corps of Engineers pinniped research lead, said the downward pattern of steelhead and white sturgeon numbers should warrant concern from fish managers.
Many challenges for fish
Threatened and endangered fish species face a multitude of issues.
Traditionally, wildlife officials sharpened their focus on the four “H”s of conservation: habitat, harvest, hydro and hatcheries.
However, in recent years, predation and climate have become grander parts of the conversation, said John Edwards, Fish and Wildlife Columbia River pinniped biologist.
“It’s difficult to just show such a direct effect,” Edwards said. “With salmon conservation, there’s no one silver bullet for it.”
The Bonneville Dam, the lowermost dam on the Columbia River, is an opportune location for pinnipeds. It can delay upstream fish movement, causing fish to gather as they search for a ladder entrance. Sea lions are opportunists, easily plucking vulnerable salmon, steelhead or sturgeon lingering behind.
Many methods have been used to reduce sea lion predation at the Bonneville Dam. Officials have installed metal grates at all fishway entrances at the dam’s tailraces to block the animals from getting to the salmon and steelhead. They also use pyrotechnics and rubber buck shot as a form of hazing. Officials say that’s been a questionable deterrent, as sea lions seem to get used to the hazing quickly.
The most effective, if controversial, option is to lethally remove the sea lions.
State and tribal agencies are permitted to trap and euthanize Columbia River sea lions that prove to be “problematic pinnipeds,” those that linger in safe zones where fish are vulnerable. In these areas, the fish may be spawning or are experiencing delayed migration.
The Columbia River Inter-Tribal Fish Commission coordinates with eligible tribes to provide animal parts for educational and cultural uses.
Between fall 2021 and spring 2022, 33 Steller sea lions and 14 California sea lions were trapped and removed from the river near the dam.
A 2022 model prepared by Fish and Wildlife estimated that trapping and removing sea lions near the Bonneville Dam and Willamette Falls saved roughly 20,000 fish. That’s the amount the pinnipeds would have consumed to sustain themselves through 2035.
There are new initiatives and strategies in the mix.
Edwards said the Washington and Oregon wildlife departments plan to expand current observation areas along the mainstem to various tributaries. They are also planning how to deter new pinnipeds from journeying up the Columbia River with their more habituated cohorts.
A bumpy history
Centuries of a primal rivalry between humans and marine mammals nearly led seals and sea lions to extinction. To allow for pinniped numbers to recover, Congress passed the Marine Protection Act in 1972.
The law successfully buoyed Pacific Northwest stocks to elevated levels in the following decades. But this rebound in protected pinnipeds — juxtaposed with nosediving fish stocks — presented a new issue, particularly to fish in the Columbia River system.
California sea lions were the first pinnipeds to appear at the Bonneville Dam in the late 1980s, though only sporadically. Then came Steller sea lions in 2003.
Simply put, Columbia River sea lions were decimating already fragile fish stocks, and the waterway’s ecosystem was out of balance.
In response to pinnipeds’ risk to fish stocks, wildlife officials introduced a monitoring program in the early 2000s to document predation trends.
Assessments show Columbia River sea lions have eaten thousands of fish each year since 2002. Though Washington, Oregon and Idaho received federal authorization to lethally remove California sea lions from focus areas in 2008, Steller sea lion predation skyrocketed.
Rates of slain salmon and steelhead below the Bonneville Dam doubled between 2006 and 2015. As a result, Congress passed a law in 2018 to ease restrictions on sea lion management, but state and tribal agencies weren’t permitted to lethally remove Steller sea lions until 2020.
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