I agree with the human assitance theory. The one known male green sunfish that was loose in our pond for a few years came from our neighbors hired hand. He would go down to the creek a mile away and siene 3-4" GSF for bait before he came over to fish for LMB. This pratice was stopped as soon as we discovered it but at least one male GSF survived and a small number of pumkinseed looking hybrids were caught over the next 7-8 years. This one male was removed by my brother years ago. I have not seen a hybrid in our pond for several years now but my brother in law claims he caught an 11" plus "pumkinseed" this last July. Had I not talked with the nieghbors hired hand by chance one day, we would have never known where that one male GSF came from.