if all you do is let the fish go then it will continue to happen, call the game warden, let the law handle it. Put the number in your phone of the KDFWR, and call them, if you have a gps mark it on that and take a picture of it, most fisherman have a camera in there boat. I know there is cheating out there but would like to see it first hand to belive it is so rampent.
Just my two cents.