California and Steller sea lions have roamed the Pacific coast for centuries, but were not seen entering the Columbia River in significant numbers until the 1980s. Steller sea lions, the larger of the two species, are now present at the mouth of the Columbia River year-round, but California sea lions spend their annual breeding season at rookeries off the coast of southern California and Mexico. In fall, thousands of adult males and juveniles return north to forage for food along the west coast of North America. A 2006 survey conducted by the Washington Department of Fish and Wildlife (WDFW) estimated there were up to 1,200 California sea lions and 1,000 Steller sea lions in the lower Columbia River.
Since the early 1980s, California sea lions have been moving in increasing numbers farther and farther up the Columbia River – first to the Astoria area, then to the Cowlitz River and on to Bonneville Dam, 145 miles from the river mouth. In recent years, California sea lions have been reported above Bonneville Dam, with occasional sightings in Drano Lake and McNary Pool.
Like California sea lions, Steller sea lions have been observed feeding below Bonneville Dam in recent years, but their primary prey is white sturgeon rather than salmon and steelhead. In 2008, the U.S. Army Corps of Engineers observed 17 Steller sea lions consume 606 sturgeon in the tailrace below the dam, which represented 98 percent of the predation documented by sea lions on sturgeon that year. By contrast, California sea lions accounted for 96 percent of the predation on salmon and steelhead that year.
1st of May, 2012