Minecraft wiki entry for Turtle_farming, associated text: If you wish to have the turtles leave the farm area, you can add temporary slab (to each module) to the right of the current slab. However, place it on the bottom of that block rather than the top, to provide a staircase of sorts. Only do this when you have all adult turtles in the farm, and go to the outside with some seagrass to attract them to the outside. Once they've left, remove the temporary slabs, to prevent future baby turtles from also escaping on them.