In most ponds, if you want to support a population of trophy bluegill it will require some sort of harvest strategy. While it is true that vast populations of smaller, lower Wr largemouth bass can prop up a quality bluegill fishery, there are things that you as an angler can do to promote the possibility for the bluegill of a lifetime.
Most experienced bluegill anglers have seen high densities of agressive, nest defending males during the springtime. If you sneak up on these fish you will often find the best bluegill fishing of the year, as these protective males hammer any offering in their reach. It would seem intuitive that these bigger fish should be returned to the water. Well, that's correct, but not entirely for the reasons you'd guess.
These biggest, most agressive males are usually in the higher echelon of the size distribution, but these fish are going to spend vast amounts of energy in nest building, nest protecting, gamete formation and fry guarding. During some of the peak growing season these fish are too preoccupied with nesting to be actively pursuing available prey items, and consequently aren't growing as well as they could be. But their size and agressiveness are why they've been able to secure the best spawning sites.
So what happens to all the other males in the pond?
If the big nest guarding fish are quality nine-inch fish, then there is often a grouping of younger males that are 7 to 8 inchers and can't compete for the best nesting sites. Since these smaller, younger fish can't get the best nests, studies suggest that they will skip most of the rigors of spawning and, instead bulk up on available invertebrates so that come next spawning season they can have a chance to compete. By leaving the older, bigger fish on their beds and not harvesting, or overly disturbing them you are setting the table for an entire additional class of big males the following year.
Think of it as an investment.
So what can you do if you love bluegill filets spattering a little grease on the floor next to your stove?
How about harvesting females? If you spend some time learning identification of male vs. female characteristics you can put heavy pressure on female fish for eating. This makes it virtually impossible to harvest over one half of your adult fish, and allows more males to reach their potential.
If you want to get really sophisticated you can even learn to identify fish by their relative weights and harvest fish that aren't thriving as well as others. And this includes males too. If your average Wr (relative weight) in your pond or small lake is 95 for example, you can harvest fish that are below that mark and protect fish that are above. This may (and I stress MAY) improve the overall genetics of your pond by selecting for fish that are better adapted to your particular pond environment.
So make harvest part of your overall management strategy, but do it wisely to give you the best chance of growing huge bluegill.