Here is a thought. Hire someone to electrofish the pond and take out all the small LMB and Crappie you catch. That has two advantages. One you get to take them out quick and select any real healthy ones to leave in. Two you take out LMB across the spectrum of catchability. If you just fish for them then you are taking out the fish that tend to bite lures (catchable) and leave in those that are not catchable. Just fishing over time makes the job of removing them harder because the ones left tend not to bite lures.