Manatees can grow over 13 feet in length and weigh up to 3,500 pounds. Their eyes are small, but eyesight is good. Manatees have a nictitating membrane which can be drawn across the eyeball for protection. Manatee vocalisations take the form of chirps, whistles and squeaks. Peak energies are in the 3-5 kilohertz range.
Communication is particularly frequent between mother and calf, or when the water is turbid.
Manatees vocalise to express fear, anger, pain or sexual arousal. They are also adapted to hear infrasound frequencies below 20 hertz. Swimming speeds of up to 20mph have been recorded, but normally manatees prefer to cruise at speeds of at 2-6mph. They will typically surface to breathe through their nostrils every three to five minutes. When they are using a great deal of energy, however, manatees may surface for air as often as every 30 seconds.