A California sea lion munches on a salmon near Bonneville Dam along the Columbia River. (Photo By: Oregon Department of Fish and Widlife)
But California and Stellar sea lions also showed up at Bonneville Dam in major numbers and devoured the second largest number of salmon and steelhead on record.
Those are the conclusions of an Army Corps of Engineers report on 2016 salmon predation as the annual sea lion removal program kicked off in early March.
"In 2016, observers documented the second highest pinniped abundance since monitoring began [in 2002]," the Corps reported. In all, 190 sea lions ate 9,525 fish, or almost 6 percent of the adult run between Jan. 1 and May 31, 2016.
Sea lion predation is a huge issue for ratepayers in the Northwest since one-third of Bonneville Power Administration's wholesale power costs to electric co-ops is tied up in fish and wildlife protection.
Using a special federal authorization, wildlife managers in Oregon and Washington in 2016 captured and euthanized 59 California sea lions known to be habitual fish consumption offenders.
Those actions seem to be paying off in reduced fish mortality, at least for California sea lions (CSL), the Corps said.
"In addition to the largest removal of CSL to date, most of the animals that have returned to Bonneville Dam for several years were among those removed. By the end of the 2016 field season, only two CSL had been present at Bonneville for longer than two seasons."
However, no similar capture program exists for Steller sea lions, and they made major inroads into the endangered fish population in 2016. Twenty-seven of that breed had camped out at Bonneville Dam for at least two seasons, according to the Corps.
"While the impacts of CSL removals on predation rates may be positive for salmon, the increasing presence and consumption rates of SSL is concerning and may warrant a management strategy in the future," it noted.
The trapping program appears to be more effective than non-lethal deterrents, such as scaring sea lions with pyrotechnics, the Corps added.