Re: Alaskan Pattern Productivity, What Works;
The general or accepted belief is that once the fish enter into the fresh water and their final stages of sexual maturity they are no longer eating as a means of gathering additional proteins / caloric energy for continued growth. The biochemistry changes and the brain sort of reprograms with the imprint of memories of the scent and chemical properties of the natal waters of each individual. There is believed to be a certain level of geomagnetic influence involved in their migratory patterns while in the oceans also, but that isn't what you ask.
Food & Spawning:
Even though the fish undergoes many changes as they enter the final stage of life the behavior learned in the years at sea or in a large lake are not completely expunged from the brain. When you fish close to the lake or ocean they seem much more aggressive as they are just beginning the transition from the feeding - growth way of life they are accustomed to. As they continue their journey up a river or creek the continuing development of the reproductive organs and components require all sorts of changes not the least of which is hormonal. By the time they are in the river for a week or 2 they have moved even farther away from that 'eat to live' way of life that they have known since birth. Think of it like this; fish have no sense of time so the physiological changes that they undergo are all that there is in their lives at any given moment.
The bright and gaudy colored flies are the predators best play to draw the attention of the fish in hopes of triggering that instinct to grab small things that swim. Dark or natural colored flies work well also but you have to get these a bit closer for reasons of visibility. The exception to this 'trying to get them to strike' occurs once they have established spawning beds and are actively engaged in defending every inch of territory. While they are especially vulnerable at this time there are 2 important reasons why this is not a good time or place to target them. By the time salmon begin the actual bedding and spawning actions their bodies have degraded to such a significant level that they no longer will make suitable table fare. The second of the important reason is that this is now the nursery water and continued disturbance of the fish although it may not completely interrupt the spawn, in some cases it will. When stressed at this point males will release their milt and females may release the eggs.
There are times when I am trout fishing using trout tackle and while not targeting salmon will catch fish that are well into the spawning ritual. Almost always the fish are subordinate males who have been forced away from the spawning site by the dominate male. I do not knowingly swing flies over beds, I fish behind or above visible fish searching for trout who hang around with them. No matter whether you are looking to catch these subordinates or not, it happens. Actually it happens so often that I can say that these fish are so aggressive that they can't be kept from a fly. At this time color of the fly does not need to be considered, dark, light, no difference.
Most or perhaps all of the lake run fish in the Colorado area are land locked sockeye salmon. These fish are notorious as being hard to draw to a fly whether in Alaska or in a land locked system in the lower 48. My best advice is to be as close to the mouth of rivers and creeks that get these fish and try to present bait-fish imitations to them before they get 50 miles and 2 weeks into the rivers. It would have been better to set you up with silver / Coho salmon perhaps.
I don't know if I answered the question or not. I just started typing, the information I offer is based on several sources. What I have read, what I have seen, and what I've actually done - learned hands on. Bottom line = some species are just more likely to grab a fly than others. You may find it interesting that trout here will grab a Skykomish Sunrise or Freight Train as readily as they will a good Sculpin imitation. I hope all this proves either helpful or at least interesting.