It is our opinion that we should stay of the redds as much as possible. Why? The redds are the active breeding grounds of these spawning fish. The female fish will dig out a nest from the gravel using her tail. She then lays her eggs as the male fertilizes them. After this, both will defend the redd from others, females supposedly from other females who would try to homestead upon her redd and the males from males who would try to weasel his way into propagating his genetic makeup on an already fertilized redd. During this defensive posturing, the female buries the redd and both parents leave, the male to continue his efforts of genetic flow and the female to eat and return to lower areas of the waterway, or in some species, both will die within days of completing the spawn.
The redds are an important part of the existence and continuation of the species that use this system to spawn. It is in our opinion that those fish should be unmolested while on the redds.
But what about the fact that the fish you lost when they weren't spawning, those fish had spawning potential. You're absolutely right, those fish did have spawning potential, they had potential to grow and become monsters in their own right, and challenge another fisherman in the years to come, that is why it's horrible when that fish lost its life. That fish, though, could have lost its life in a hundred different ways; being taken by an eagle, mink, or bear to name just a few unique ways. The fish that made it to the redds made it! They are there doing what nature has instilled in them to do. Attempting to fish the redds is tripping a runner right before the finish line.
We are not going so far as to say that we cannot or should not fish that are actively working their way to the spawning grounds. No, those fish are fair game, they are still open to natural predation and circumstances that are going to end their life. They have not reached the finish line and that gauntlet that they run is full of perils. Steelhead and salmon are two examples of fish that have become legendary for fisherman who seek them. They are legendary in their instinct to return to their spawning grounds, to leave the ocean that they have called home for years to return to the small streams and ditches that they forgot about for so long. To be part of that, to be witness to this event, with a fly rod in hand is nothing but majestic. To be another hurdle that they must face is to be one with our primal self.
As always, Good Luck and Guid Luck!!