I have two yellow metal yard sticks screwed into the boat one in front and one in back.
Also have my live well divided to keep the fish divided for two fishermen.
If I have a third person in the boat I will use a stringer.
I fish in MO a lot and by law you can not remove a fish from the live well to cull.
You decide to cull as you catch.
Also you have to be able to identify who caught what fish.

In a canoe on the Buffalo River, I mark my fishing rod