Spawning has to do with water temps.
Size has to do with food sources available. The biggest fish are the ones that have a steady diet of bunker.
WHERE they spawn is related to if they were born there. Fish return to the rivers they were born in. If netters or fishermen take too many out of one population, that single population will suffer more than the others.
Some pretty cool videos I found.
another one
Cool vids thanks for the shares.
another one
Fishporn is much better than plugporn any day. Thanks for sharing.