Manatees

SCIENTIFIC CLASSIFICATION

COMMON NAME:	manatee, sea cow
KINGDOM:	Animalia
PHYLUM:	Chordata
CLASS:	Mammalia
ORDER:	Sirenia
FAMILY:	Trichecidae

GENUS SPECIES:	Trichechus inunguis, the Amazonian manatee. The Amazonian manatee is the smallest of the manatees. Several physical characteristics distinguish it from the other two species. It lacks nails on its pectoral fins, and usually has whitish patches on its underside.
	Trichechus manatus, the West Indian manatee. There are two subspecies of the West Indian manatee: the Florida manatee (Trichechus manatus latirostris) and the Antillean manatee (Trichechus manatus manatus). These subspecies are distinguished by differences in cranial measurements and by their geographic distribution.
	Trichechus senegalensis, the West African manatee. About the same size and shape of the West Indian manatee, the West African manatee differs in some important respects: position of the eyes, snout, and cranial bones.

DESCRIPTION:	The manatee's body is streamlined - full around the middle and narrowing to a paddle-shaped tail.
	The true color of a manatee is gray, although it may appear brownish gray. Amazonian manatees usually have white or pink patches on the belly and chest.
	Organisms such as algae, which may grow on the skin of slow-moving individuals, alter the body color and make some manatees look more green or brown.

SIZE:	Adult West Indian and West African manatees average about 3 m (10 ft.) in length. Large individuals may reach lengths of up to 4 m (13 ft.).
	Amazonian manatees are the smallest of all three species. They are shorter and more slender. The longest specimen measured 2.8 m (9.2 ft.).

WEIGHT:

Average adult weights are approximately 363 to 544 kg (800-1,200 lb.). One particularly large Florida manatee weighed 1,655 kg (3,650 lb.). Females are generally larger than males. A particularly large Amazonian manatee individual weighed 480 kg (1,058 lb.).

DIET:	Manatees are primarily herbivores. They feed on a wide variety of submerged, emergent, floating, and shoreline vegetation. Manatees in Florida feed on more than 60 species of plants including turtle grass, manatee grass, shoal grass, mangrove leaves, various algae, water hyacinth, acorns, and hydrilla. Manatees consume about 4% to 9% (15 to 49 kg or 32-108 lb. for an average adult manatee) of their body weight in wet vegetation daily.
	In Sierra Leone, Africa, the West African manatee is considered a pest because they consume fields of planted rice.
	Manatees have occasionally been seen to eat foods other than plants. Antillean manatees have been known to eat fish from nets and West African manatees have been known to eat clams.
	Some Amazonian manatees living in deep bodies of water apparently fast during dry seasons (November and December) when water levels drop as much as 9 to 15 m (30-50 ft.), eliminating their access to vegetation.
	Because manatees have a very low metabolic rate, it is speculated that Amazonian manatees are able to fast for up to seven months if necessary.

GESTATION:

The exact gestation period of most manatee species is not known and is poorly studied. It is known, however, that a Florida manatee's gestation is approximately 12 months.

RANGE:	All living manatee species are found in warm tropical and subtropical waters.
	The West Indian manatee was once abundant throughout the tropic and subtropical western North and South Atlantic and Caribbean waters. However, the manatee's numbers have been greatly reduced and is rarely seen throughout its range.
	The range of the Florida manatee is primarily peninsular Florida but extends as far north as Rhode Island. Manatees have been rescued near Houston, Texas, and Mississippi.
	Antillean manatees have a patchy distribution throughout the Caribbean, Mexico, and northeastern South America. The southern range extends through Central and South America to Brazil.
	West African manatees range from Senegal to Angola, on the west coast of Africa.
	Amazonian manatees are the only species of manatee confined to fresh water. They inhabit the Amazon Basin, mostly in Brazil. They are uncommon or close to extinction in Peru, Ecuador, and Colombia.

HABITAT:	The West Indian and West African manatees inhabit rivers, bays, canals, estuaries, and coastal areas rich in seagrass and other vegetation. They can live in fresh, saline (salt), and brackish waters. They move freely between extremes.
	West Indian manatees may be found in any waterway over 1 m (3.25 ft.) deep and connected to the coast. They prefer waters with temperatures above 21°C (70°F). Florida manatees rarely venture into deep ocean waters. However, manatees have been spotted as far offshore as the Dry Tortugas Islands, approximately 81 km (50 mi.) west of Key West, Florida.
	West African manatees live in quiet coastal areas, large rivers, lagoons, and connected lakes, where the water temperature is above 18°C (64°F).
	The Amazonian manatee is restricted to fresh water. They are most common in floodplain lakes and channels in white-water river systems with water temperatures ranging from 25°-30°C (77°-86°F).
	The patchy distribution of manatees throughout all their ranges is due to their search of suitable habitat: plentiful aquatic plants and a freshwater source of water to drink.

POPULATION:	GLOBAL	Populations of all species of manatees have apparently declined over the past hundred years. These declines are due to such causes as hunting for their meat, destruction of their habitats, boating, pollution, and low reproduction rates. Antillean, Amazonian, and West African manatee populations are not known due to inadequate scientific research.
POPULATION:	REGIONAL	An aerial census is done at least once a year on the Florida manatee. The Florida manatee census taken in February, 2004, found 2,505 individuals. The 2005 survey was 3,143. These figures represent the minimum amount of manatees known to be in the state of Florida at the time of the census.

STATUS:

IUCN

All four species of sirenians are endangered or threatened. The Florida manatee is one of the most endangered marine mammals in the United States.

A manatee can move each side of its lip pads independently. This flexibility allows the manatee to "grab" aquatic plants and draw them into its mouth.
Manatees do not have eyelashes. Their eye muscles close in a circular motion, much like an aperture on a camera. They have a lid-like membrane (called a nictitating membrane) that closes over their eyes for protection when they are under water.
Manatees can hear very well despite the absence of external ear lobes.
A manatee's heart beats at a rate of 50 to 60 beats a minute. The heart rate slows down to 30 beats a minute during a long dive.
Manatees have no "biting" teeth, only "grinding" teeth. A manatee's teeth (all molars) are constantly being replaced. New teeth come in at the back of the jaw and move forward about a centimeter a month. The front molars eventually fall out and are replaced by the teeth behind them. This tooth replacement is an adaptation to the manatee's diet, as it consumes plants that may hold a lot of sand.
Manatees have only six cervical (neck) vertebrae. Most all other mammals, including giraffes, have seven. As a result, manatees cannot turn their heads sideways, they must turn their whole body around to look behind them.
The manatee's rib bones are solid, there is no marrow. They make red blood cells in their sternum where marrow is found.

The manatee has pelvic bones, but they are not attached to its skeletal frame. They are remnants of a time when manatees lived on land. The bones are found in a cartilage tissue area of the body in the vicinity of the reproductive organs and the urinary bladder. The bones are soft when the manatee is young and later harden as they mature.
Other remnant bones found in the manatee are the hyoid bones located near the neck region. These bones are similar to the Adam's apple in humans. Today, there is no known use of these bones in the manatee.
The manatee's lungs lie along its backbone instead of along its rib cage as is found in most mammals. The lungs are long (1 meter or more in adults), wide (20 cm), and thin (5 cm or less). Besides breathing, the lungs help the manatee with buoyancy control.
The bones in a manatee's flipper are similar to a human hand. The jointed "finger bones" of the flipper help the manatee move through the water, bring food to its mouth, and hold objects. Three or four nails are found at the end of each flipper.
The adult manatee averages about 10 feet long and weighs about 1000 pounds.

Manatee Behavior Movement
A manatee uses its flippers and tail to steer itself through the water and moves its tail up and down to propel itself forward. Manatees are quite agile in the water. They can swim upside down, roll, do somersaults or move vertically in the water.

Breathing
Manatees are mammals. They must surface approximately every five minutes to breathe, but can hold their breath for as long as twenty minutes when resting. The manatee's nose is usually the only part of its body that comes out of the water when it breathes.

Feeding
Manatees are herbivores, which means they eat plants. Also known as a "sea cow," manatees usually spend up to eight hours a day grazing on seagrasses and other aquatic plants. A manatee can consume up to 10 percent of its body weight in aquatic vegetation daily. The manatee uses its muscular lips to tear plants much like an elephant uses its trunk.

Do manatees have teeth?
Manatees have molars but no front teeth (no incisors or canines). Manatee teeth are unusual among mammals because they are continually replaced throughout the animals’ lives. The teeth are sometimes called “marching molars” because they erupt at the back of the jaw and move slowly forward. As old molars fall out at the front of the jaw, new molars replace them. Scientists believe this is an evolutionary adaptation to a coarse diet of seagrass often mixed with sand.

Do manatees need fresh water to survive?
It is unknown whether fresh water is essential for manatees’ survival, but they do like it. Manatees can be found in rivers and springs as well as congregating at fresh water drainage pipes. Some people attract manatees to their docks by letting them drink water from ordinary garden hoses. This is illegal and endangers the mammals because it brings them to areas of high boat traffic.

How big are manatees?
The average Florida manatee is about 10 feet long and weighs close to 1,200 pounds. Manatees can reach up to 13 feet in length and weigh 3,500 pounds. Female manatees tend to be larger than the males. Their calves weigh around 66 pounds and are 4 feet long.

How long do manatees live?
Manatees in captivity have been known to live for more than 50 years. Distinctly scarred individuals have been known to live for at least 39 years. Dead animals are aged from microscopic examination of growth layer groups (annual layers, similar to the growth rings in trees) in their ear bones.

How many manatees are in Florida waters?
As of 2001, the highest number of manatees counted in a statewide survey was 3,276. However, this is only the highest count of the number of manatees in Florida and is not a true estimate of the population.

How many types of manatees exist?
There are three species of manatees in the world. The West Indian manatee ranges along the coasts and inland waters of the southeastern United States, eastern Mexico, the Greater Antilles, and Central America to as far as northern Brazil. It is comprised of two subspecies: the native Florida manatee is found throughout Florida and neighboring states, and the Antillean manatee found throughout the rest of the species' range, including Puerto Rico. The other two species include the Amazonian manatee, found only in the fresh waters of the Amazon, and the West African manatee, found in the rivers, estuaries, and coasts of western Africa.

How often do female manatees give birth?
After reaching sexual maturity at 4-7 years, female manatees give birth to an average of one calf every two or three years. The calf stays with its mother for up to 2 ½ years.

What is the range of the manatees?
Manatees are found throughout rivers, springs, and shallow coastal waters of Florida and nearby states. Manatees have been seen as far west as Texas and as far north as Virginia. Though they like to stay near warm waters, adventurous ones such as “Chessie,” a manatee tagged with a satellite transmitter, was tracked all the way to Chesapeake Bay in 1994. Scientists feared he would not make it back to Florida before the cold weather approached, so they flew him home by plane. The next summer, he journeyed to Rhode Island and returned on his own to the Ft. Lauderdale area. In 1996, he headed north again, losing his transmitter in North Carolina.

What state and federal laws have been enacted to protect manatees?
They are protected under two federal laws: the US Endangered Species Act of 1973 lists manatees as endangered; they are also protected under the US Marine Mammal Protection Act of 1972. In response to mounting evidence of the negative effects that boats have upon manatees, the state legislature also passed the Florida Manatee Sanctuary Act in 1978, allowing the state to establish and enforce boating restrictions in important manatee habitats. The responsibility for administering the law now lies with the Florida Fish and Wildlife Conservation Commission.

What threatens manatee survival?

Habitat Loss–Coastal development and pollution can seriously harm manatee habitats by affecting their main food source, seagrass.
Watercraft–Collisions with boat hulls and propellers have caused approximately one quarter of all manatee deaths since 1974 (when record keeping began). Manatees feed on seagrass beds in shallow water where there is little time or room to dive to the bottom to avoid oncoming boats. Death may result from propeller wounds, impact, crushing, or any combination of the three.
Entanglement–Discarded crab traps and fishing gear cause problems for many marine species, including manatees. Manatees can also ingest harmful debris.
Canal Locks and Flood Gates–Manatees are sometimes crushed in gates or killed by asphyxiation.
Poaching–Historically, manatees have been hunted for their meat, hide, bones and fat by Native Americans and European settlers. Manatees were in high demand in the late 1800s. Hunting is now rarely a problem.
Natural Causes–Manatee deaths can result from things like sudden freezes, non-infectious diseases, birth complications, natural accidents, red tide (such as the one in March and April of 1996), and other natural catastrophes.

Why do manatees seem drawn to power plants?
During the cooler months, warm water discharge from power plants and other industries attracts the manatees because they can’t survive extended exposure to cold water. When the surrounding water temperature drops below 68° F or 20° C, they move to warmer waters, including southern Florida, power plants, and natural warm water springs. Historically, the manatee population was concentrated around South Florida during the winter months, but the power plants on coastal and inland waterways have made it possible for them to survive winter in northern Florida if they have access to a warm water site.

How fast are manatees?
Tracking studies have shown that manatees can travel up to 50 miles or 80 km in a day. Manatees generally swim slowly but have been clocked at speeds up to 15 mph (25 km/hr) for short bursts.

How long can manatees stay underwater without breathing?
While time varies with the animals’ level of activity, manatees surface to breathe about every four minutes. When resting, they can stay underwater up to 20 minutes before surfacing for air.

How much do manatees eat?
Manatees, feeding between 6 and 8 hours daily, consume about 4 to 9% of their body weight in wet vegetation such as seagrass and other aquatic plants.

Credit: Florida Fish and Wildlife Conservation Commission , Sea World, USGS