Salman. Yes and no. Way back, in an effort to increase the size of Skamania summer steelhead they spawned the big fish only. The larger fish spent and additional year in saltwater so they got bigger. Worked super except for one thing. Marine survival was too low to replace the brood. The additional year of mortality reduced returns below egg-take needs.

There is a reason why there are multiple age classes and it is not so that anglers can catch big fish. We need all the pieces. Plus, since age at maturity tends to be inherited if you focus on one age at maturity you run the risk of run failures. Remember that there is no safety net with pinks. A huge flood and you get damn little back.

As to the other questions about increasing adult size and fecundity the managers (or at least knew when I was involved) what needs to be done. In simple terms, increase the food base so they have food to eat. Stop killing any and all immature fish, which means having NO marine mixed stock fisheries. Limit fisheries to maturing adults in the bays/rivers. It ain't rocket science, it had been known for decades, but the political opposition is too great.

Then, you throw a warming ocean that is also getting more acidic, a human population that keeps expanding, and you have a recipe for failure.