NORTH BONNEVILLE, Wash. — One by one, curious California sea lions checked out the open cage left invitingly on a platform in the Columbia River below Bonneville Dam and flopped inside to chill out on the nice flat surface.

Big mistake.

Around noon the door clanged shut and state agents concluded their first day of trapping the salmon-hungry sea mammals. The sea lions weren’t having much fun behind bars Thursday, but it beat the bullet between the eyes some came within a whisker of getting under a federal removal authorization.

A day earlier, the 9th U.S. Circuit Court of Appeals ruled that some of the animals could be trapped but not killed in reply to a lawsuit brought by the Humane Society of the United States.

The sea lions are protected by a 1972 federal law. An amendment, however, leaves open the possibility that some can be captured or killed if the states request it. Oregon and Washington did in 2006 with the support of Indian tribes and sport and commercial fishing groups.

The National Marine Fisheries Service authorized removal of about 85 animals a year for five years, but recommended limiting the annual take to about 30 and suggested capture take precedence over killing, to which the states agreed.

Thursday’s haul was eight. Two were endangered Steller sea lions that had to be freed. Two had brands identifying them as among 61 that federal authorities had marked for immediate removal and the status of one is uncertain. The others were unbranded or branded and not targeted for removal. Those will be hauled to the mouth of the Columbia River and freed.

Washington State Fish and Wildlife spokesman Craig Bartlett said the traps were not baited but were left knowing the animals would use them “just as a place to haul out.”

One of those targeted and caught, branded as C319, has been raiding salmon at the base of Bonneville Dam for at least five years, Bartlett said.

The fish gather at the dam each year as they wait to go up fish ladders to upriver spawning ground and are easy pickings for the sea lions who follow them.

The targeted animals are destined for the Point Defiance Zoo and Aquarium in Tacoma, Wash., where Sea World veterinarians are to arrive today to examine them. Sea World has agreed to take 12. State and federal officials say they have commitments for homes for 19 or 20.

As indignant barkings came from the trapped animals, others thrashed in the river near the base of the dam gobbling salmon. Sea gulls wheeled overhead in hopes of a scrap.

The Humane Society sought an injunction against killing or removing the animals for this year to give the whole case a chance to be heard in court. It took the case to the federal appeals court when it was rebuffed.

The group argued, among other things, that this year’s spring Chinook run is expected to be unusually large and the animals proposed for removal would not have the “significant negative impact” required by the amendment to the 1972 law. The appeals court agreed.

The salmon and the sea lions usually are gone by early June, making it highly unlikely any sea lions will be killed this year. Trapping is to resume next week, Bartlett said.

Bartlett said there is a chance other homes may be available for sea lions in future years. He said no sea lions have been transferred from the wild to a zoo or aquarium since the 1990s, and that the captive sea lion population is getting older.

Fishermen and Indian tribes say the animals eat up to 4.2 percent of the spring Chinook run, putting pressure on salmon runs the federal government tries to preserve at great expense.

The Humane Society has long argued that there are heavier pressures on the runs, such as dams and bird predation, and noted that the allowable salmon catch this season has been increased by a third.