Here is another snip I found on this subject. Of course not sure how concrete any of this is....

Bluegill are an important species when it comes to fisheries management. Bluegill provide an excellent forage for bass due to their ability to reproduce at incredible rates. During one summer, a female bluegill can spawn three times releasing 2,300 to 81,100 eggs per spawn. This rate of reproduction is necessary to maintain adequate bass forage in a balanced bluegill/largemouth bass fishery and is why bluegill are preferred over other sunfish species.

The only difference between a rut and a Grave is the depth. So get up get out of that rut and get moving!! Time to work!!