I may just have to settle for being able to pick salmon from trout - lol.
From what I've read this weekend, all-black mouth & gums = chinook, black mouth with white gums = coho, white mouth & gums = atlantic. If that's always true, then it was a coho. The tail spotting seems atypical though - along the upper edge as you'd expect but also along the lower edge. I don't know if mouth coloration or tail spots are rules or just true most of the time.