Manatee, West Indian

Trichechus manatus

phylum: Chordata

class: Mammalia

order: Sirenia

family: Trichechidae

status: Vulnerable, IUCN Endangered, ESA

range: Bahamas, Belize, Brazil, Colombia, Costa Rica, Cuba, Dominican Republic, French Guiana, Guatemala, Guyana, Haiti, Honduras, Jamaica, Mexico, Nicaragua, Panama, Puerto Rico, Suriname, Trinidad and Tobago, USA (Florida, Georgia), Venezuela

Description and biology

The West Indian manatee, also known as the Florida manatee, is a large marine mammal with a rounded, heavy gray body and a horizontally flattened tail. An average West Indian manatee has a combined body and tail length of 8 to 13 feet (2.4 to 4 meters) and weighs 800 to 3,500 pounds (360 to 1,590 kilograms). It has small eyes and no ear pinnas (external flaplike portions). The animal's nostrils are on the upper surface of its snout and can be tightly closed by valves when the manatee is underwater. Manatees often rest just below the water's surface, coming up to breathe every 15 or 20 minutes. They use their flexible flippers almost like hands for eating, moving through seagrass, touching, holding a nursing calf, and even hugging other manatees.

The manatee is the only marine mammal that feeds solely on vegetation. It eats a variety of aquatic plants, including water hyacinths, hydrillas, and seagrasses. The manatee is often called a sea cow because it grazes on marine seagrass meadows. It uses its split upper lip to grasp food and pull it into its mouth. Primarily a nocturnal (at night) feeder, the animal can consume up to 100 pounds (45 kilograms) of food a day.

Manatees have no particular breeding season, but most births seem to occur in spring and early summer. After a gestation (pregnancy) period of 13 months, a female manatee gives birth to one calf, which is about 4 feet (1.2 meters) long and weighs 60 pounds (27 kilograms). Even though it begins grazing on vegetation within a few months, the calf continues to nurse from its mother for one to two years.

Habitat and current distribution

The West Indian manatee is found in the coastal waters and rivers of Florida and Georgia, Central America, and the West Indies. It prefers to inhabit slow-moving rivers, river mouths, bays, lagoons, coves, and other shallow coastal areas. It is at home in all types of water environments: fresh, brackish (slightly salty), and salt. The manatee requires warm water and will migrate great distances between winter and summer grounds.

The total number of West Indian manatees in existence is unknown, but a statewide survey in Florida in early 1997 listed the manatee population there at just over 2,220.

History and conservation measures

Native Americans hunted manatees for centuries, using the animals' flesh, bones (for medicine), and hide (for leather). When Spanish explorers began colonizing Caribbean islands in the sixteenth century, manatee hunting increased. Biologists (people who study living organisms) believe this hunting is responsible for the manatee's initial decline.

Natural events, such as sudden changes in water temperature, also can be deadly to manatees. In the 1980s, three abnormally cold winters in Florida lowered water temperatures throughout the state. In water below 60°F (15°C), manatees become sluggish, stop eating, and eventually die. Many manatees perished during those cold Florida winters.

The greatest continued threat to manatees, however, comes from humans. Many manatees drown each year from being trapped in fishing nets. Others are drowned or crushed by flood gates or canal locks. Some are injured by discarded fishing lines, hooks, and trash. The majority of manatee deaths in Florida are caused by collisions with speeding boats. Those animals that survive such collisions bear lifelong propeller scars.

In 1978, the Florida legislature passed the Florida Manatee Sanctuary Act, which designated the entire state a refuge and sanctuary for the animal. Manatee protection zones have been established in which boats are required to reduce their speed. In areas declared manatee refuges, no boats, swimmers, or divers are allowed. In other countries in the West Indian manatee's range, public education programs have been launched to raise awareness about the animal's plight.