I was there last year over the 4th and caught a few just about everywhere I fished. The only place that I found channel cats was off of the jet ski beach. I think if I had been a little farther up towards the inlet of the Piedra, I would have done better. But this was all last year...hopefully someone else will be able to put you on them better.
try to go fishing near arboles if you can find some crappies near the shore the catfish will be in that area. Just catch some of them and use them for bait all of the river inlets are good also. Like the pine. good luck!