I would just go over to talk n educate them first. Let them know what species, the minimum size, maximum catch limit for one day and then explain the heavy penalties (big big fines!) if they are caught doing wrong thing. Might need simple sign language if they can't communicate with you. I'm guessing new anglers like overseas students and new migrants would be the main culprits as they do not automatically know the laws. If after educating them and you see them doing it again then report them, cos after that you be a solid witness.