We did the Manatee trip in Jan. We sat for 5 minutes, watched one come slowly up, stick up a couple of nostrils and take a breath, and slowly sink back down. 5 minutes later, it happened again. Wouldn't you know, 5 minutes later it actually happened again!
One of those things you have to do at least once. On the other hand, the snorkeling was good, lunch was good, saw a bunch of dolphins also. All in all, not a wasted trip.