your permit is useless on anyone elses boat. no one is going to take you giant fishing and split the reward with you. now school tuna<73" is a different story they will just give you the fish.
on some boats is if you actually hook a giant your trip is over right then and there. the mate jumps on the rod if it's a money fish.
the capt. is not going to risk you losing HIS fish.
your trip is free. simple math. saleable fish worth 12 bucks a pound verses a days pay for the charter
