The West Indian manatee, also known as the sea cow, is a large, gentle, grayish-brown mammal that spends its entire life in the water feeding on seagrass. It frequents the coastal waters of Florida, particularly in winter, but its range extends north to Virginia, west to Louisiana, and along the coastal waters of Central and South America, as far south as northeastern Brazil. Stray individuals have been spotted in summer as far north as Rhode Island and as far up the Mississippi as Memphis.

The manatee's preferred habitat is shallow, coastal waters, estuaries, canals, and slow-moving rivers. They flourish in warm waters with a depth of 1 to 5 meters. Manatees tolerate differences in salinity, and thus can inhabit both fresh and saltwater.

There are two subspecies of the West Indian manatee, the Florida subspecies, Trichechus manatus latirostris, and the Antillean subspecies, Trichechus manatus manatus. These two subspecies are nearly identical physically and mainly distinguished by their respective ranges, with the Florida variety in the north (Florida), and the Antillean variety in the south (Central & South America). The two subspecies also have slight but measurable cranial differences.

West Indian manatees are closely related to the West African manatee, Trichechus senegalensis, and the Amazonian manatee, Trichechus inunguis, also from the family Trichechidae. A bit more distantly, they are related to the dugong, Dugong dugon, and the Steller's sea cow, Hydrodamalis gigas (extinct), from the family Dugongidae. Manatees, which have rounded tails, can be easily distinguished from dugongs, which have fluked, whale-like tails. The snout of the West Indian manatee is bent further down than the snouts of the other manatee species in the Trichechidae family.

Adult manatees are 3 meters long on average (10 ft), and weigh an average of 500 kg (1,100 lbs). Some individuals reach a length of 4.6 meters (15 ft), and a weight of 1,000 kg (2,200 lbs) or more. Females are typically larger and heavier than males. Manatees have flexible, split upper lips which pass food into their mouths. Their skin is wrinkled and they have whiskers on their snouts. Individual hairs appear sparsely on their bodies, and their skin continually sloughs off, which may help to reduce algae build-up.

The forelimbs of manatees are narrow flippers, used for steering and maneuvering along the muddy sea floor. These flippers each have 3 or 4 nails, which are reminders that manatees are distantly related to elephants. Manatees have no hind limbs, though they do have vestigial hind limb bones floating in their hind area muscle. Their tails are round, flat paddles used for propulsion. Though manatees appear fat, they are actually highly muscular, and are very agile in the water.

Manatees move slowly and spend most of their time eating, resting and migrating. They have a low metabolism and consume about 10-15% of their body weight daily. To achieve this rate, they must eat for 6 to 8 hours each day.

Manatees must surface to breathe every 2 to 4 minutes, or much more frequently-every 30 seconds-when active. Each breath renews about 90% of the air in their lungs, as opposed to about 10% for humans. Their nostrils are valved and located at the top of their snouts.

The hearing of manatees is good, and mothers and calves communicate by means of squeals and bleats. Manatees have no pinnae, or ear flaps. Eyesight is poor, though they do use their eyes for navigation. Their eyes are protected by means of a nictitating membrane, and they can be closed with a sphincter-like contraction.

The abrasive sea plants consumed by manatees cause their teeth to wear down. As a result, they have evolved molars which are continually replaced throughout their lives. The seagrass they eat ferments in their hind-gut, contributing to digestion.

Manatees have a slow reproductive rate. Females reach sexual maturity at about 5 years of age, and males at 9. They give birth to one calf every 2 to 5 years, and only occasionally have twins. They have a 13-month gestation period and calves stay with their mothers for up to 2 years. Calves nurse from their mothers from two teats located under the forelimbs.

Manatees are not considered territorial, and generally exist alone or in loosely connected groups. Pairs seen together are typically mother and calf. Large groups of manatees sometimes gather near the warm waters discharged by electric power plants.

Historically, manatees have been hunted for their meat, hide and bones. Hunting continues to this day in Central and South America. In modern times, they face the extreme danger of collisions with motorboats, and many manatees in and around Florida can be identified by the propeller scars on their backs. Manatees are also threatened by loss of habitat, which is often due to agricultural and industrial runoff. Other dangers include entrapment in flood gates and canal locks, red tides, and cold stress. They have no known predators other than man.

No one knows how many manatees exist today. Surveys of Florida manatees show a population of between 2,500 and 3,000 individuals. The Antillean subspecies is less protected and found in very small populations throughout their range. They are assumed to be fewer in number than the Florida subspecies. All manatees are endangered.

Manatees are the state mammal of Florida, and Florida is now a marine sanctuary for manatees. There are fines for killing a manatee, and they are protected by the U.S. Marine Mammal Act (1972), the Florida Manatee Sanctuary Act (1978), and the U.S. Endangered Species Act (1973).

For an illustration comparing species and species size in the order Sirenia, see: http://www.sirenian.org/caryn.html

- West Indian Manatee information assembled from published and on-line sources by Kevin Miller on Oct. 24, 2006 for SeaPics.com.

Sources: Ripple, J. Manatees and Dugongs of the World, Voyageur Press, 1999.

http://marinebio.org/species.asp?id=46

http://animaldiversity.ummz.umich.edu/site/accounts/information/Trichechus_manatus.html

http://www.sms.si.edu/IRLspec/Trichec_manatu.htm

http://www.cnn.com/2006/US/10/24/memphis.manatee.ap/index.html (Manatee finds way to Memphis; Oct. 24, 2006)