We had a sea lion infestation at the Ballard locks in Seattle. They
lazy blubberbutts would lounge around at the base of the fish ladder
and pick off salmon as if they were on a smorgasbord.

Fireworks- didn't work long term.
Phony fiberglass Orca- scared away all the phony fiberglass sea lions
Hauling the sea lions a few hundred miles away and realeasing them-
they were all the hungrier after their long swim back.

What has worked: Mooring a barge in Shilshole Bay, not far from the
locks. The barge has fencing on three sides, and a radio controlled
trap door on the fourth side. During the portions of the year when the
salmon aren't running, this trap door is left open all the time and the
sea lions get used to lounging on the barge. When the salmon are
running, they wait until the sea lions have all hauled out onto the
barge to sun- and then trip the trap door. Saves the salmon, but the
downside is that the sea lions bark and yap almost endlessly until they
are let out again- and that can be several days or more depending on
the run. Just try to sleep on your boat at the marina with 6 p-o'd sea
lions sounding off all night!