When pond owners ask me about northern pike in ponds, I usually respond with this line of thought. A good northern pike population probably will be no more than 10 pounds/acre. I have seen some higher, but a lot lower.
I ask the landowner what size of pike they would like to catch, on average. Usually, they'll say 3 or 4 pounds. Well, that means about 3 fish per acre, and let's say they have a 3-acre pond. An entire fishery dominated by 9 adult pike? Not much food value there, is there?
As already mentioned, northern pike can be eating machines, and when they are abundant, they can decimate a panfish population. They really knock back yellow perch, and in extreme circumstances will also affect bluegills. The problem is that the pike like to eat prey items that are 33-40% of their body length. So, a 24-inch northern pike will seek something like an 8-10 inch perch, the same fish that anglers want to harvest.
I used rotenone to renovate a gravel pit lake for a fellow a few miles from my hometown. He complained that all he had was stunted yellow perch and black bullheads. It was about 1.5 acres in surface area. We put in the rotenone, and very little happened. Then, up came three northern pike, all between 5 and 6 pounds. That about 15-18 pounds of pike in 1.5 acres of water (10+ pounds/acre). The pond also contained yellow perch, green sunfish, and black bullheads. These other fishes were NOT stunted. They were low density, all small fish, and very plump! The northerns had them all cropped down. I'll bet we didn't kill 20 pounds total for those other fishes. If they had been "stunted," it would have been hundreds or even over a thousand pounds. (By the way, this gravel pit now has a dandy smallmouth bass population, and the pond owner calls it his "aquarium" for fish watching.)
I will admit that lower-density northern pike populations don't cause these kind of problems. However, it's hard to control exactly what will result.
For most pond owners, the best advice is probably to leave out northern pike.
Dave
