OK that's marginally encouraging... but you gotta remember that chum have little reliance on the riverine environment beyond adequate spawning gravel. They leave the stream almost immediately after becoming free-swimming fry. Since they spend so little time in-river, there are few instream selection pressures affecting the natural juveniles beyond surviving chance catastrophes during their incubation in the gravel. Virtually all the selection takes place in the marine phase of their life cycle.

This is one species where the artificial boost in egg-to-fry survival from being coddled in a hatchery actually makes sense.

In contrast, the genetic integrity and fitness of other salmonids which are held in the hatchery's holding ponds for a prolonged period of time prior to release (steelhead, coho, chinook, sockeye) will certainly suffer from the domestication effects of being raised in captivity.