The legal size limit is 65 mm (carapace), to ensure that animals caught have had a chance to breed. If a crayfish loses a leg or feeler, a new one is grown but then their overall growth is slower. It is therefore important not to damage undersize crayfish.
Place one end of the measuring device firmly into the groove between the antennae and measure from this groove to the rear edge of the carapace. Hairs do not form part of the carapace. Divers are required to measure crayfish at the first available opportunity before the crayfish is bagged.