The North Willamette River is a major tributary of the Columbia River and flows through Portland, Salem, and Eugene. Historically, the Willamette saw winter steelhead migrations in much higher numbers–20,000-40,000 fish. However, a range of factors, including water conditions, dams, habitat degradation, and predations have drastically reduced runs. The number of returning winter steelhead that migrated past Willamette Falls dropped to 512 adult fish in 2017.
Sea Lion predation is a very real threat to migrating salmon and steelhead, and the issue is only exacerbated by dams and fish ladders. Essentially, these man-made structures and natural river features like Willamette Falls congregate the salmonids and create a ‘buffet’ for sea lions. It is estimated that sea lions consume 20-25 percent of fish that migrate past Willamette Falls.
Responding to growing pressure to reduce the number of sea lions, the Oregon Department of Fish and Wildlife initiated a sea lion killing program to help these endangered salmonids. In 2019, 33 sea lions were lethally removed from Willamette Falls. The removal, along with improved water conditions, has helped winter steelhead in the river system. As of today (April 7th), 4,869 winter steelhead have crossed the Falls. An estimated 900-1,100 winter steelhead would have been eaten and not spawned without the removal of these sea lions.
As a caveat, successful salmon and steelhead recovery will require far more than just removing sea lions. Dams remain the premier impediment to full recovery. Additionally, competition from hatchery fish, pollution, ocean conditions, and other forms of predation also pose serious threats to these endangered populations of salmon and steelhead. But in any event, allowing an extra 1000 winter steelhead the opportunity to spawn is a success.
For more on this development, check out this article from The Statesman Journal.