Where I worked before, the Bonneville Dam fish trap, I did not take pics of the fish. I wish I would have, because over the years I handled some dandy springers and steelhead - the size you wouldn't think were around much anymore. While we did note all of the different scars and wounds, we did not photo-catalog them.

This is the closest thing I could find on the web, in a short time. Pics 9 and 10 in this gallery are interesting. Not a pacific salmon but interesting the same.

http://theriverscourse.blogspot.com/2012/03/landlocked-love-for-deep-green-beauty.html

I should have phrased my post a bit less definitively. This may very well be a remnant, vestigial twin that has been reabsorbed in a location and in a shape that is common to a lamprey scar, but it's "exceedingly unlikely". The spots are interesting but not conclusive, in my mind - skin does all sorts of weird things when it reforms, particularly if the wound is deep, hair where the re wasn't before, etc.

I'm sticking with the lamprey scar, you guys can have the "Ripley's" conclusion...

:-)