Doc Donaldson did that run-time changing with his UW salmon. Essentially, they selected for early coho and late Chinook. So, the students were introduced to the pond with coho that were both smaller and not as "important" research-wise. Then, in November and December when we were more experienced and the weather and water were a damnsite cold the Chinook came in.
Ma Nature does it to. What survives to spawn is what produces the next generation and that survival includes size, return time, age at return, willingness to bite a hook, and probably a myriad of other aspects.
Atlantic salmon males in some streams responded to total fishing pressure (probably the marine gill net) by never smolting. The females needed the growth to get big eggs, but the sperm didn't need the added size.