Here's another observation remembered, goaded by Silver's post about large vs. small fish.
Big swirls and splashes do NOT mean big fish. Sunfish of all species, in schools, are very competitive. Small sunfish make the largest commotions near the surface. On top water bugs, the larger the splash, many times, the smaller the fish. I believe this is because the little ones are trying to "get a bite" before a larger fish cruises in and eats the whole thing. Shiners, chubs and other schooling fish act/react the same way.
Unless you're seeing the fish making the commotion, don't assume it's as big as the swirls make it seem.