I'd seine or trot line. Get a nice long trot and put multiple offerings on it. See what they go for, and what they don't. They are not like common carp, they eat different stuff. You need to find out preferences, then chum that in places you see them. I guess for free your friend might want them. But the bigger they are, the less value they have as far as vegetative control. Too large of pond for snagging. And shooting at water is dangerous to say the least.
