Ive been fishing my friends private lake for about a year now.
The lake is about 10 acres .

Heres the situation.

I have fished the Lake about 80 times. In my 80 trips, I have caught 99.9% LMB , and 1 (yes 1) bluegill)
Last year I didnt think much of it when i caught alot of 6-8 inch LMB and only a couple that reached 10 inches .

This year While fishing, the LMB are all still 6-8 inches , though they dont look "stunted" (not really sure what a astunted bass looks like) ?

I see large schools of LMB in the 3-6 inch range , im assuming they are the young of the year, But these schools are ALL OVER THE LAKE . I mean every 10-15 yards there is one of these large schools of fish.
I NEVER see any bluegill, or bluegill fry , And im positive there is no Bullhead in this lake.

Im worried that My friends private lake has no predator/prey balance at all.

is there a better way to understand the relationship than just what I catch and see?

What if anything can I do to help my friends lake out ?

Would stocking only a few Adult Size Bluegill be a good choice?
Or perhaps bluegill fry?