It's been dead since the middle of July for mantas. That can change suddenly. We had some strange coral and algae blooms in Kona this last month, don't know if that affected their eating patterns. I'm going out tonight, if anything shows up I'll add a brief note.
Call Big Island Divers when you get in, they keep track, as well as Jack's and a few others, and they'll give you the straight poop on whether they've seen mantas the last few nights.
Steve
Update: We had 2 mantas tonight. There was good plankton and the mantas were feeding for the entire time divers were around. Hopefully it'll start picking up again, it tends to run in spurts.