I think you can start harvest now, be thinking your 9-11" fish. If you see a runt, skinny 8 from same year class add him to the bunch - doing nothing but tying up carrying capacity. Maybe give the 12" fish a chance to keep going and return them. I don't think you could possibly affect their population through casual angling where it was negatively impact reproduction. It only takes a few adults, and infrequent successful spawns or low recruitment helps you with future management, so I'd say harvest away.