Any salmon that aren't caught on their way 'home' or that are not collected by eagles, bears, ravens and seagulls in the stream will die in the same water in which they spawned - and in which they themselves were spawned some years before. You'll see salmon bodies littering the banks of the rivers or crumpled behind boulders or rotting where they were dropped by the replete bears. It is not in any sense a waste because the elements are released into the water and will feed the fry in time to come.