The West Indian manatee (Trichechus manatus) — sometimes called the sea cow—is found along the coast of Florida and in the Caribbean. Most adult manatees are about 10 feet long and weigh 800 to 1,200 pounds, although some larger than 12 feet and weighing as much as 3,500 pounds have been recorded. These “gentle giants” have tough, wrinkled brown-to-gray skin that is continuously being sloughed off. Hair is distributed sparsely over the body. With stiff whiskers around its mouth, the manatee’s face looks like a walrus without tusks.
Christopher Columbus was the first European to report seeing a manatee in the New World. To Columbus, and other sailors who had been at sea for a long time, manatees were reminiscent of mermaids—the mythical half-fish, half-woman creatures of the ocean. Manatees are not fish, however, but marine mammals.
The manatee maneuvers through the water moving its paddle-like tail up and down and steering with its flippers. It is very agile for such a large animal, sometimes somersaulting and doing barrel rolls in the water.
The manatee often rests suspended just below the water’s surface with only the snout above water. It feeds underwater, but must surface periodically to breathe. Although the manatee can remain underwater for as long as 12 minutes, the average time is 4-1/2 minutes.
Manatees are herbivores, a term that means they eat only plants. They consume 4 to 9 percent of their body weight each day—that’s 32 pounds of plants for an 800-pound animal! To do this, manatees spend 5 to 8 hours a day eating—typically non-native water hyacinths and hydrilla, along with native aquatic plants such as Vallisneria or eelgrass.
Manatees move between fresh- water, brackish, and saltwater environments. They prefer large, slow-moving rivers, river mouths, and shallow coastal areas such as coves and bays. The animals may travel great distances as they migrate between winter and summer grounds. During the winter, manatees congregate around warm springs and around power plants that discharge warm water. During summer months, they have occasionally been seen as far north as Virginia and Maryland.
Manatees reach breeding maturity between 3 and 10 years of age. The gestation period is approximately
13 months. Calves may be born at any time during the year. Usually a single calf is born, but twins do occur. An adult manatee will usually give birth to a calf every 2 to 5 years. The low reproductive rate makes the species less capable of rebounding from threats to its survival. Newborn calves weigh 60 to 70 pounds and are 4 to 4-1/2 feet long. They nurse underwater for about three minutes at a time from a nipple located behind their mother’s forelimb. Born with teeth, calves begin eating plants within a few weeks but remain
with their mother for up to 2 years. Manatees may live for several decades.
Manatees communicate with each other by emitting underwater sounds that are audible to humans. The vocalizations, which sound like squeaks and squeals, are especially important for maintaining contact between mother and calf. One field report described a mother and her calf, separated by a flood gate, calling to each other for three hours without interruption until they were reunited.
Manatees face many threats to their survival throughout their range. Historically, they were hunted for their flesh, bones, and hide. Manatee fat was used for lamp oil, bones were used for medicinal purposes, and hides were used for leather. Hunting is thought to be largely responsible for the initial decline of the species; however, hunting is no longer allowed in countries where manatees are protected.
Today, the greatest threats to manatee survival are collisions with boats and, in Florida, loss of warm water habitat.
- U.S. Fish and Wildlife Service, http://www.fws.gov/endangered/esa-library/pdf/manatee.pdf, accessed 21 March 2012