Looks like a brown at 1st but... I have not seen a brown with a sharp cut nose like that. Almost a angle on top of the nose. Most brown male should have a orange color. But since this one is little odd... So did a sort little search. Guess what? It's not a brown.
http://www.miramichisalmon.net/fishing.html
Image from that site.
"Fall Atlantic salmon are far different in appearance than the summer salmon as they are a little darker, having red and orange spots."
I hope there were no "Atlantic salmon" that was keep by people that thought it was a brown.
Edit: Nice that you chought a Atlantic salmon... but to bad about the keeping part.
The moral of the story... If you don't know what it is, don't kill it?