We did the harbor-walk during the late afternoon on the thanksgiving day 2012.
We saw couple of manatee near the deck eating sea grass at the beginning of the boardwalk walk. There was a warning sign for boats about manatees so we guess manatees are frequently seen at this place. Harbor water was clear enough and there were not many boats docked so we saw them well and up close.
We could see lots of big Tarpons swimming along with them. One of the restaurants located along the harbor walk feeds the fish and pelicans there at 4.00pm in the evening. The pelicans there seem to know the exact time and place this feeding happens so we could see them gathering near the restaurant. We waited there to witness the feeding but they announced that they don't have enough fish to feed. Don't know whether this is the usual case.
There are lots of places to ear and shop along the harbor walk. Boat tours also provided for a a fee. We saw some tall sail ships too.