These are chain pickerel? How in the world did only chain pickerel get in his pond? Were they stocked purposely?

If the pickerel are surviving then what other fish are in there that they are eating? Are there LMB in there or other predators? Bluegill or hybrids?

Any known CC or other catfish in your friend's pond?

Do you get any sense of how many pickerel?

also you need to think about vegetation or safe refuge in shallows or around structure. If there is plenty of refuge then the BG at 1500 stockers can hold their own against pickerel and some will survive, grow up, and spawn and soon there will be too many BG.

From all the people on this forum who wished they had NOT stocked CC, I would say in a 2 acre pond 30 CC would be plenty (assuming they had a good chance to survive) Soon they will find ways to reproduce and you will truly have a CC problem unless you are dedicated to catching and keeping them. They would not have a natural predator in that pond except human angling and removing.

The pickerel are not as voracious and destructive of a predator as LMB or CC and I wouldn't kill them off either. They are a neat fish, very desirable by some pond-meisters for their unique position as a selective predator with a limited gape size potential and built in limit to how much and what they eat.