Mich. Comp. Laws § 324.47312
The department may authorize the taking of trout, whitefish, and yellow pickerel for the purpose of fish culture at any time during the open or closed seasons provided in this part, when it is determined by test nets set under the direction of the department that at least 20% of the fish taken are females and at least 40% of these females are ripe and ready to spawn. However, when all spawn needed for state and federal hatcheries has been secured, the department may close all commercial fishing during the remainder of the closed season. The department may close all commercial fishing during the closed season on those grounds that are so located as to prevent proper handling of spawn or where it appears that little or no spawn is being taken.
MCL 324.47312