Grew up down in SoCal, rarely did we hook a halibut when fishing in the bays. The State instituted a 21" min size limit to allow the fish to grow to adulthood and spawn a time or two before being subject to harvest. If not mistaken, California halibut mature around 18", so a 21" limit gave them a season or two to spawn.
10 years later when I fished in San Diego bay, it was uncommon to NOT hook halibut, mainly shorts but the occasional legal one. Seems to me it worked pretty well.
Similar thing happened in Chesapeake Bay too. Years ago the various jurisdictions there had different size limits. One or two had a size limit the allowed the take of fish that weren't of spawning age. Populations in the Bay were on the verge of crashing. Seems, again as I recall, the interested parties got together and used a limit that allowed fish to spawn at least once before being eligible for harvest. Worked pretty good from what I've heard.
Imagine shooting spotted fawns and seeing what happens to you local deer population.
