I did an internet search right after asking - shoulda done it before asking, but hey, I don't always think straight at 3 AM in the morning... Thanks for the reply, DWF!
They reach into southern Ohio, and that's why I've never seen them. I've fished northern OH/PA straight down to here in FL, but never the Mississippi or directly off of it. Sure, when fishing the Ohio river in PA we'd catch some interesting fish, but never anything like that. Supposed to be some monster cats in the Ohio at the dams though.
The sites I visited stated that while they were a bear to clean, they were actually good eating (though by whose standards I have not a clue).
So now I have a reason to visit over there - fishing tourism at its finest.