I've experienced similar problems, and have really restricted who can fish the ponds. I was at a good friend's place earlier in the week. It is a place where we've done a lot to cleanup three old ponds. One of the ponds still has a lot of green sunfish that we are slowly getting under control.
They invited a neighbor over who says he loves to can those things and would take out as many as he could catch. He unfortunately also took out a number of 12-14 inch catfish we put in last year, and some of the big bass that have been getting the green sunfish under control. His excuse was that he doesn't believe it is healthy for a pond to throw back anything that gets caught.
I don't think he'll be invited back.
