I have never heard about a successful removal of northern pike from any waters by fishing. The biggest predator of small and medium pike is larger pikes. So most of the time the biomass of pike stays the same and the average size declines when eradication by fishing is attempted. The pike uses flooded vegetation for spawning, so lowering waterlevels during spawning may help.
But the best way to deal with "unwanted" pikes is to realize that they are there to stay (like herpes) and live with it. pikes are great gamefish and does not diserve to be

poisoned

. People who thinks poison can save or help a situasjon like that of a pike invasjon should go sit in the corner and dont come out til the glaciers return.
Poison was tried as a way of clearing rivers of parasit riden salmon in Norway, but sinse the fjords are sites for fishfarming of salmon, the new populations of salmon that reinvaded the "empty" rivers was quikly contamined in the fjords, and the salmon is now declining or gone from the rivers again.
This is the ONLY situasjon poison may have worked, if it had not been for fishfarming.
Poison is for poisoners, personaly! I cant express how sad and low it makes me feel when i hear people actualy preposing things like this. We do not own the fish in the rivers, the water or any organism in it.