If its a stellar sea lion, ESA is absolutely a "problem"
California sea lions and harbor seals are protected under the rules of the marine mammal protection act (MMPA) which not only prohibits the "taking" aka killing, hunting etc, but prohibits harmful acts against them.

NOAA has attempted to define which deterrents are acceptable when it comes to protecting fishing gear, persons or property. But its debatable what their jurisdiction really is and how it applies in the real world.

As far as I know, there are no treaties or tribal rites that slip under the wire with regard to the ESA and MMPA rules.

With that said, it seems a little irrelevant to debate and discuss a managed harvest, a retail market, or even a "use" for seal and sea lion carcasses to any degree at all. The first post in the thread is a question of "who" will do it, rather than the more difficult question of "how" to get it done with the ESA, MMPA, and animal rights groups holding them both up.
ESA is a huge hurdle, but even without it, the MMPA isnt going away. Animal rights/special interest groups would tie up any proposed changes in court for decades.

Tribal rites and/or treaties isnt a back-door by any means at all.

Of course it makes perfect sense to consider population management while keeping protective rules in place. But theres no motivation to implement management other than the hostile claim from fishermen that sea lions and seals are eating "our" salmon. No-one cares.

Seals/Sea lions have an impact on salmon, some of which are protected themselves- most of which are dwindling in numbers by historical comparison. But I cant say I completely disagree with the unpopular opinion that anglers/commercial fisheries/consumers need make the sacrifice to protect the populations of fish prior to the extermination of a predator that relies on them for food- because from a neutral standpoint, its hypocritical for anglers to site the cause for killing sea lions as "sea lions kill endangered/protected salmon"... when we are killing them too.

Im not riding a fence with carnivore instinct on one side, and a love of all things on the other. I love to fish I love to eat fish. But Ive accepted the fact that the resource is faced with huge challenges that are not the result of sea lions and seals eating.
So who can realistically look at either for a remedy? Especially when over-harvest combined with continued habitat destruction/loss keeps predation on the far back-burner... where it belongs IMO.

Im sure I am not the only idiot who accepts it as fact that by the time the lawyers, judges and politicians figure it all out, there wont be any salmon left to fight over. So I'll get mine while the getting is good and I'm not going to lose a wink of sleep when Mr sea lion gets his.