These 3 members (ages 16-20) have been advised by myself and other club members that what they are doing is illegal and that if we catch them they will be be turned in to the authorities as well as being removed as members of our hunting club.
You already know what they are doing. So why haven' t you done anything yet?
You don' t have to catch them if you already know what' s going on.
To allow them to keep hunting that way is saying it' s ok.
Do something!