They are highly migratory and move from one place to another. They tool up and down the coast, following the food supply, females and even showing their calves where to go to be safe. You are definitely in manatee habitat in the Putnam County area.
All a manatee needs, we have found, is a chance to get out of the way of an oncoming boat. We have scientific proof that manatees can sense a boat and attempt to move away. A fast boat doesn't give the slow moving animal an opportunity to get out of the way.