There are many of these types of boat creatures - alligators, manatees, dolphins, pelicans, sting rays, crabs, ducks, herons and a plethora of other creatures we have yet to encounter on our travels.
Even though one may feed, hold, cuddle, pet their boat creature who lives on board, it is better (and, sometimes, the law) to not mess with any of the boat creatures around the boat. Talk to them, take pictures if you desire to do so, but don't attempt to feed, pet, touch or swim with them. Even a docile looking creature such as a dolphin can get his "fin out of joint" and inflict injury.
On our entire trip thus far, I have yet to encounter an alligator or a manatee. Keith has seen both, but not I. Manatee's, apparently, make appearances in the morning hours after sunrise. I admit, those are not my favorite hours of the day. I'll wake up around 9'ish and Keith will come down into the cabin and tell me all about the "huge manatee that was swimming around the Sue" - no picture, no rushing down to wake me up so I can rush up and take a pic. So, I now have this insatiable goal to see a manatee. Maybe one day <sigh>.
While in Seabrook, my favorite boat creature were the ducks. Now, we did feed them crackers or day-old bread. During breeding season, we would get a Mama Duck and Daddy Duck with their passel of ducklings paddling around the boat every evening around 5 pm waiting patiently for their bread or crackers. I laugh when I think about it. They were a close-knit brood until feeding time - than it became "every duck for himself". They would chase each other away to fight for that bread or cracker crumb.