Howdy,
One boss I used to turn wrenches for(a music promoter running a tune-up shop?) would get upset if I didn't save the heads from my Salmon/Steelhead for him, fishhead soup was his favorite food in the world.
As far as wastage, I can remember how upset I was finding a large amount of sliced open Chum carcasses up on the N.F. Stilly for the first time. I now realize the importance of spent adult fish in stream/riparian foodchains. This ingredient was overlooked (still is with max. sustained harvest policy) until a few years ago. The importance of woody debris was recognized around the same time I believe. More quality fishing should result from the emphasis on stream protection. Salmon don't care if they spawn in urban conditions, as long as we make it possible.