It may be as simple as the use of slot sizes . Leaving the ones in short supply and taking out some of the ones in the too many size. I would think you need to get the big pike out but maybe leave a few small ones. But my best advice is gather data by catch, seine and traps - then compare RW (relative weights). You can post the results and we can see the results and let you know. You could also hire a fisheries scientist. The best thing you could do is get Dave Willis or his students to look at the lake as northern waters like yours are his specialty .