I have observed this on a number of occasions, and its rewarding to finally prove your observation by catching the fish. I've found that "large" is often relative to the size and location of the stream. A 10 - 14" brookie is a large fish in some locations (Lancaster County, for instance); a 17" brown is a small fish in many locations but is a nice sized fish for some streams I fish here as well.
The first two pictures are of a hole that should have a whole school of fish in it. There's usually a little guy that lives under the rock that has a tree growing on it in the foreground of the first picture. The second picture is taken from the vicinity of the tree in the foreground of the first picture; the large rock on the left is undercut, and there are plenty of smaller rocks up near the waterfall for cover. But up in the flow, I have never really caught anything, until finally catching the bully of the hole last Wednesday. She taped out at 10".
The next set of pictures is one of the better holes on another stream that usually has one other smaller fish that chases anything, but is too nice of a hole to only have that fish living in it. It is about a three to four foot bowl; the left rock is deeply undercut and the two rocks sticking up in the foreground mark the bottom part of the bowl. I finally landed the bully of that hole last year. It also was 10" but was a much fatter fish than the one I caught last Wednesday (although of course they were from different streams). This year, I caught a smaller fish there, so I'm thinking the bigger fish may have succumbed over the summer.
The last batch of photos is from a drainage in NC PA. It is mixed brown/brookie habitat, but in the holes where I have never caught fish, my bet is on there being a big brownie there since that is what has turned up in holes where I have caught bigger fish.
IMG_1696 - 15" brown (2007), 21" brown at night (2008), 13" brown at night (2011); have seen a handful of brook trout, caught maybe one or two over a 10 year period, but its a huge hole and should be loaded with fish; it has a nice batch of suckers, nay brownie snacks, that live in it and is the perfect hole for growing a very large brown trout on a small freestone stream.
IMG_1723 - deep undercut root system that gave up a 18" brown in 2009; in 2010 and 2011, it was teeming with smaller fish, indicating the bruiser was gone
IMG_2921 - beautiful, deep hole; who knows how far back under the rock the water goes; have NEVER seen a fish in this hole
IMG_3061 - a bit of an anomaly; this hole teemed with fish AND had at least one 18"+ fish in it in 2010 that chased but wouldn't commit
IMG_3049 - deep hole; hard to fish, had a 18"+ fish in it in 2010 that also chased but wouldn't commit (more of a factor of the fisherman not paying attention and about crapping his pants when it darted out after the offering!)
061807 151 - I believe I finally saw and caught one small fish out of this hole last year, but in five years prior to that, nada...
To me, this is one of the more interesting aspects of fishing; first, its being outsmarted by a fish that has grown wise enough over its four or five years of life to not show its face right away; second, its going back the next year and (in some cases) outsmarting the fish by catching it; third, its going back the next year to find that the cycle has completed itself and a hole devoid of fish is now full of them, indicating the fish died or moved on for some reason. There's a wild card involved, I think, from the floods last fall. While many fish survived, I believe that some fish perished in the floods, and thats why some holes are dead this year.
Jim Bashline called these fish "sharks"; I like the idea of The Alpha Fish, or The Bully.
