I've put over 400 days in at LJ in the last couple of years, I know many other friends that fish hard as well, and I have never seen nor known someone who has seen a dead sea lion OTW, gunshot or otherwise.
Wasn't there a story last year of sea lions being killed for their gonads (apparently considered an aphrodiasic in some parts of the world)? Might not just be anglers popping them.
