Just a note to Bill's comment. In cool water (up north)YP will eat a lot of small BG (< 3 inches) when the water cools as their metabolism is still high when the BG's start to slow. Easy pickings for the YP. Several studies on this. YP are no where near the best predator to control BG as SMB , WE , HSB and LMB can do the same thing on a larger scale. LMB not so much when the water cools as their metabolism is close to that of BG. There are non predator methods of reducing BG as well. Neither YP , SMB or HSB will alone in normal numbers control BG up north and there is doubt if LMB can either if the BG get a big head start on them. You will have to manage the populations by various methods but that is why you have a pond in the first place.