Although I have not caught a lot of ripe coho however I have caught a good many of this specie in general. I will guess the fish in the picture in the 14 -15 lb range. I think we may be able to agree that 15 pound is not a small fish. The only reason I sent the picture of that silver to Dan was that as I had said earlier, it was bigger than most king salmon I catch. I am not meaning to disparage the fish you landed but my experience with these fish started in 1989 working as a commercial fisherman in the gulf of Alaska and the Cook Inlet fisheries. We saw a lot of salmon. Having been a salmon fisherman since 1979 also helps me to keep perspective when I think back on fish landed. From Atlantic salmon Grilse and Landlocks to the Great Lakes and their tributary rivers and now resident here in Alaska I have seen a few salmon. The point of reflecting on this one fish was that it seemed to stand out as being exceptionally large as in depth and fatness. I have never before or since seen one like it and I do regret not retaining it until it could have been certified by the State.
[Edit] Had to look around the auxiliary drive a bit but found this picture taken by a fellow I took on a float trip. We managed a few bright fish but I had the honor of getting hold on this one. John had never salmon fished so we photographed the catch and took notes for his record of the trip. The colored male I am holding was a 30' 10 1/2 lb and Johns' fish went 27" and about 8 3/4 lb.
Silvers don't hump up like Pink salmon do. However their morphology does change as they ripen into the spawning stages, hence the visual difference in size and appearance between the two fish. The ripe male exhibits a noticeable rise in the area behind the head and this will become more pronounced as the fish ripens. This is thought to be an asset when the males are showing for hens and competing against each other over the Redd's. The humping makes them look larger to their adversaries thus helping them to drive out the competition. Although the fish in the pictures only differed by 3" of length and 1 3/4 pounds the ripe fish does appear to be much larger
This was the best example I could produce of variances in appearances between fresh and ripe male coho salmon. The fish that Dan ran the formula on was caught in tidal water as it was exiting the ocean to a river. The fish was just plain big (for lack of a better term) and I was fortunate to have landed such a specimen. I certainly wish you the same kind of good fortune on your next visit to the Alaskan fisheries.