The smolt from two wild parents are F1's, First Generation, once removed from their Native environment. If let to reproduce on their own, they have an 85% fitness! but their smolt hatched in the native environment! return to full fitness. The problem lies in hatchability, the pair of wilds, on average can be expected only to produce two returning fish. But in captivity the number could return 2-4% or 20-40 returning adults, the key would be to release early before imprinting, so they return to their native environment, even with an 85% fitness you could expect to return not the average two as the wild counter parts! but an average of 1.70. But that would be multiplied by the 20-40 returning adults from the original F1 pair.