The West Indian Manatee (Trichechus manatus) is a manatee, and the largest surviving member of the aquatic mammal order Sirenia (which also includes the Dugong and the extinct Steller's Sea Cow).The West Indian Manatee, Trichechus manatus, is a species distinct from the Amazonian Manatee, T. inunguis, and the West African Manatee, T. senegalensis. Based on genetic and morphological studies, the West Indian Manatee is divided into two sub-species, the Florida Manatee (T. m. latirostris) and the Antillean Manatee or Caribbean Manatee (T. m. manatus). However, recent genetic (mtDNA) research suggests that the West Indian manatee actually falls out into 3 groups, which are more or less geographically distributed as: (1) Florida and the Greater Antilles; (2) Central and Northern South America; and (3) Northeastern South America

Physical description

Like other manatees, the West Indian Manatee has adapted fully to an aquatic life style, having no hind limbs. Pelage cover is sparsely distributed across the body, which may play a role in reducing the build-up of algae on the skin. The average West Indian Manatee is approximately 3 meters long, and weighs between 400 and 600 kg, with females generally larger than males. The largest individuals can weigh up to 1,500 kg (3,300 lb) and measure up to 4.6 m (15.2 ft). The Manatee's color is gray or brown.

Habitat and geographic range

As its name implies, the West Indian Manatee lives in the West Indies, generally in shallow coastal areas. However, it is known to withstand large changes in water salinity, and so have also been found in shallow rivers and estuaries. It is limited to the tropics and sub-tropics due to an extremely low metabolic rate and lack of a thick layer of insulating body fat. During summer, these large mammals have even been found as far north as Rhode Island.

The Florida manatee, (Trichechus manatus latirostris) a subspecies of the West Indian manatee, is the largest of all sirenians. Florida manatees inhabit the most northern limit of sirenian habitat. Over three decades of research by universities, governmental agencies, and NGOs, have contributed to our understanding of Florida manatee ecology and behavior, which is more than we know about any other species. They are found in fresh water rivers, in estuaries, and in the coastal waters of the Gulf of Mexico and the Atlantic Ocean. Females usually have their first calf when they are about 4 years old. Normally they only have one calf every 2-5 years, but there are rare occurrences of twins. The family unit consists of mother and calf, which remain together for up to 2 years. Males aggregate in mating herds around a female when she is ready to conceive, but contribute no parental care to the calf. Florida manatees may live to be greater than 60 years old in the wild. The biggest single threat to Florida manatees is death from collisions with recreational watercraft.

The other subspecies of the West Indian manatee is sometimes referred to as a Caribbean manatee (Trichechus manatus manatus). Antillean manatees are sparsely distributed throughout the Caribbean and the NW Atlantic Ocean, from Mexico, east to the Antilles, and south to Brazil. They are found in French Guiana, Surinam, Guyana, Trinidad, Venezuela, Colombia, Panama, Costa Rica, Nicaragua, Honduras, Guatemala, Belize, Mexico, Cuba, Haiti, Dominican Republic, Jamaica, and Puerto Rico. Historically Antillean manatees were hunted by local natives and sold to European explorers for food. Today they are threatened by loss of habitat, poaching, entanglement with fishing gear, and increased boating activity. Several of Sirenian International's scientists study Antillean manatees in Belize, which may be the last stronghold for the subspecies. Funds for research, education, and conservation projects are desperately needed in other Central American nations.

Behavior and food

The West Indian Manatee is surprisingly agile in water, and individuals have been seen doing rolls, somersaults, and even swimming upside-down. Manatees are not territorial and do not have complex predator avoidance behavior, as they have evolved in areas without natural predators.

The West Indian Manatee is an opportunistic feeder, with large adults feasting on nearly 9 to 30 kg(20 to 65 pounds) of sea grasses and plant leaves daily. Because manatees feed on abrasive plants, their molars are often worn down and are continually replaced throughout life. They are also known to eat invertebrates and fish.

Reproduction

Although female West Indian Manatees are mostly solitary creatures, they form mating herds while in estrus. Most females breed successfully between ages of seven and nine, however, females are capable of reproduction as early as four years of age. Gestation period lasts from twelve to fourteen months. Normally, one calf is born, although on rare occasions two have been recorded. The young are born with molars and premolars, allowing them to consume sea grass within the first three weeks of birth.

Manatee relationship with humans

The West Indian Manatee has been hunted for hundreds of years for meat and hide, and continues to be hunted to this day in Central and South America. Illegal poaching, as well as collisions with speeding motorboats, are a constant source of manatee fatalities.

Due to their low reproductive rates, a decline in manatee population may be hard to overcome. They enjoy protection from the U.S. Endangered Species Act of 1973, and the U.S. Marine Mammal Protection Act of 1972. However, in April 2007, the U.S. Fish and Wildlife Service announced that the West Indian manatee population of Florida had rebounded. It advised that the species be reclassified as "threatened" rather than "endangered".

Federal wildlife officials had to ignore scientific criteria they put in place in 2001 and assume the threats facing manatees will not increase.

A computer model produced for the federal study shows a 50 percent chance that the current statewide manatee population of about 3,300 could dwindle over the next 50 years to just 500 on either coast.

Contrary to what the USFWS has recommended, the Florida manatee subspecies (Trichechus manatus latirostris) has recently (October 2007) been listed as Endangered by the IUCN on the basis of a population size of less than 2,500 mature individuals and a population that is estimated to be in decline by at least 20% over the next two generations (estimated at ~40 years) due to anticipated future changes in warm-water habitat and threats from increasing watercraft traffic over the next several decades.

References

External links

• ARKive - images and movies of the West Indian manatee (Trichechus manatus)
• Animal Diversity Website: Trichechus manatus
• West Indian manatee from sirenian.org

it: Trichechus manatus