Sarah, keeper of the life jackets, asked,

What sort of sounds do they make?

Mantees emit sounds that are within human auditory range. They make sounds such as squeaks and squeals when frightened, playing, or communicating, particularly between cow and calf. No air is released from the manatee when these sounds are made, and it is not clear where the sounds are being produced or if they serve any other purpose.

Manatees are mammals and breath air through their noses at the surface - with nostrils which close tightly when submerged. They breathe every few minutes when active or swimming, and every 10 to 15 minutes when resting. They are capable of exchanging 98% of their lungs capacity in one breath. Their lungs are very large, and are also used for buoyancy control. The rushing sound of a deep exhale and breath sound much like a snorkeler. This sound, and the associated "footprint" left by the manatees tail and body at the surface are clues which reveal the presence of manatees in the area.