Male manatees (bulls) are sexually mature by about nine to ten years, although some have produced viable sperm at two to three years of age.
Female manatees (cows) are sexually mature as young as three years of age.
As manatee aging studies progress, sexual maturity may be estimated more precisely.
Although females are usually larger than males, it is very difficult to tell the sex of an individual animal without observing its underside. There is no marked sexual dimorphism other than the position of the genital openings.
The female's genital opening is located just in front of the anus. Two additional ways to identify a female are the presence of a suckling calf, or an extremely round appearance during pregnancy.
The male's genital opening lies just behind the umbilicus (navel), about midway down the underside of the body.
Mating takes place in the water in a variety of postures.
Breeding herds consist of one cow in estrus accompanied by several bulls. An estrus female can be pursued for weeks by several males. The cow often twists and turns violently, apparently to escape her suitors. The bulls meanwhile attempt to remain adjacent to her, presumably competing with each other to become the first to mate with her.
While in estrous, cows may mate with several bulls. Cows do not form permanent bonds with bulls.
Manatees breed well in captivity, but it is not known how successful the offspring would be if released. Since space is limited at zoological facilities, emphasis is placed on the rehabilitation and reintroduction of injured manatees instead of breeding them.
Zoological institutions in Florida are on a voluntary breeding hold. Until the numerous problems are corrected in the manatee's natural environment, a breeding program will not be beneficial to them.