It may be that the large bluegill are there but are in the middle of the pond. I have been fishing with live bait, but generally in more shallow water. That being said, even when the bluegill are bedding (on the full moons) I still don't catch the large ones -- the small ones seem to be the ones that bed.
I don't believe large bass are preying on the large bluegill. The bluegill I was catching in April 2002 were nearly 1 pound in size, so they would be bigger than that now and the bass are barely 2 years old. There's no way a 2-year old bass is going to swallow a bream that big.
Assuming nothing has happened to the large bluegill (someone shocking the pond or fishing out the large ones), what should be my management strategy in order to achieve my goal of being able to catch (and harvest) large bluegill on a regular basis? Should I continue to pull out all the small bluegill that I catch and leave all the bass in the pond?