My good friend, who first taught me how to tie flies and fly fish, is on the cover of that issue! His son got the cover spread, and wrote a great article on fly fishing culture. I'm very proud of him and his work!
In answer to your question, it looks like a coho. Thick caudle peduncle, plus dark tail which is indicative of a coho. I can't see the tail clearly though to tell with 100% certainty. For example, I can't see spots on the back or on the dorsal side of the tail that would also indicate the fish as a coho. I also can't clearly see the mouth - black mouth with white gums would indicate a coho. The "watermarks" sort of look like a chum, but they could be markings after the fish has been dead and lying on surface which tends to cause discolouration. There's also a white tip on the anal fin - but I've caught lots of coho with this marking before as well. Overall, I'd guess the fish is correctly labelled as a coho. But I'm guessing at this point...