This could be a poaching problem. In a 1 acre pond, a poacher keeping everything caught could take out much of the LMB population very quickly, and make a nice dent in the larger panfish. This might have allowed a few remaining RES to spawn prolifically with high fry survival, generating massive numbers of juvenile RES.
The good news is that if this is the case and the pond just has a bunch of small RES and not much else in it, the solution is simple and relatively inexpensive: put in BG and LMB. Sounds as if forage won't be a problem for the first year.
