Same can be said for trout fisheries with minimum sizes. In ID, a friend did his MSc on the special trout regs. The stream with C&R had Westslopes that were 16-18". The stream with a 13" minimum had fish up to about 13.1". It worked because the 13's had spawned once, but they never got big and old.

Spawning populations are made up of the fish that live to spawn. Weed out the faster growing fish (hit minimums sooner), the potentially older ones (exposed to fisheries longer) and you get smaller, younger spawners. This has been known to managers and researchers since at least the 70s. We can't claim that we didn't know what we were doing.