Manatees: Facts About Sea Cows

The manatee is a large marine mammal with an egg-shaped head, flippers and a flat tail. Manatees are also known as sea cows. This name is apt, due to their large stature; slow, lolling nature; and propensity to be eaten by other animals. However, despite the name, they are more closely related to elephants. Though they may seem like cumbersome creatures, manatees can swim quickly and gracefully.

Manatees range in size from 8 to 13 feet (2.4 to 4 meters) and can weigh 440 to 1,300 lbs. (200 to 590 kilograms). They have large, strong tails that power their swimming. Manatees usually swim about 5 mph (8 km/h), but they can swim up to 15 mph (24 km/h) in short bursts when they feel a need for speed, according to National Geographic.

Habitat

There are three species of manatee: the Amazonian manatee (Trichechus inunguis); the West Indian manatee, or the American manatee (Trichechus manatus); and the African manatee (Trichechus senegalensis). Their names indicate the regions in which they live. Typically, manatees stay in rivers, seas and oceans along the coast of several countries. The African manatee lives along the coast and in the rivers of western Africa. The Amazon manatee lives in the Amazon River's drainage, from the headwaters in Colombia, Peru and Ecuador to the mouth of the Amazon in Brazil. Their range is estimated to be around 2.7 million square miles (7 million square kilometers), according to the International Union for Conservation of Nature (IUCN).  The West Indian manatee lives in the southern and eastern United States, although a few "vagrants" have been known to reach the Bahamas, according to the IUCN.

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Habits

Manatees often swim alone or in pairs. They are not territorial, so they have no need for a leader or followers. When manatees are seen in a group, it is either a mating herd or an informal meeting of the species simply sharing a warm area that has a large food supply. A group of manatees is called an aggregation. An aggregation usually never grows larger than about six individuals, according to the Save the Manatee Club.

Diet

Manatees are herbivores. At sea, they tend to prefer sea grasses. When they live in rivers, they consume freshwater vegetation. Manatees also eat algae. According to National Geographic, a manatee can eat a tenth of its own weight in 24 hours. That can equal up to 130 lbs. (59 kg).

Offspring

During mating, a female manatee, which is called a cow, will be followed around by a dozen or more males, which are called bulls. The group of bulls is called a mating herd. Once the male has mated, though, he takes no part in the raising of the young.

A female manatee is pregnant for about 12 months, according to Save the Manatee Club. The calf, or baby manatee, is born underwater. The mother helps the calf get to the water's surface for air, and within the first hour of life, the calf will be able to swim on its own. In five years, the young manatee will be sexually mature and ready to have its own young. Manatees usually live about 40 years.

Classification/taxonomy 

According to the Integrated Taxonomic Information System (ITIS), the manatee's full classification is:

• Kingdom: Animalia
• Subkingdom: Bilateria              
• Infrakingdom: Deuterostomia              
• Phylum: Chordata
• Subphylum: Vertebrata
• Infraphylum: Gnathostomata              
• Superclass: Tetrapoda              
• Class: Mammalia
• Subclass: Theria
• Infraclass: Eutheria
• Order: Sirenia
• Family: Trichechidae
• Genus:Trichechus
• Species: Trichechus inunguis (Amazonian manatee, South American manatee), Trichechus manatus (West Indian manatee, American manatee, Caribbean manatee), Trichechus senegalensis (African manatee, West African manatee)
• Subspecies: Trichechus manatus latirostris (Florida manatee), Trichechus manatus manatus (Antillean manatee)

Conservation status

The IUCN's Red List of Threatened Species lists all manatees as vulnerable or endangered and facing a high risk of extinction. Populations are expected to decline by as much as 30 percent over the next 20 years. Numbers are hard to come by, especially for the secretive Amazonian manatee; the IUCN says the estimate of 10,000 manatees should be regarded with caution because the numbers are supported by little empirical data. Similarly, the exact number of African manatees is unknown, but the IUCN estimates there are fewer than 10,000 manatees in West Africa.

The Florida manatee and the Antillean manatee were listed as endangered in 1967 and 1970, respectively, under the Endangered Species Preservation Act of 1966; the number of mature individuals was estimated to be fewer than 2,500 for each subspecies, and the populations were expected to decline by more than 20 percent over the next two generations, or about 40 years.

On March 31, 2017, however, the U.S. Fish and Wildlife Service (FWS) downgraded the West Indian manatees' status from endangered to threatened. Both significant increases in the manatee population numbers and habitat improvements led to the downlisting, according to the FWS.

As many as 6,620 Florida manatees and 6,300 Antillean manatees are estimated to live in the wild currently, according to the FWS.

"Today, we both recognize the significant progress we have made in conserving manatee populations while reaffirming our commitment to continuing this species' recovery and success throughout its range," Jim Kurth, acting director of the FWS, said in a statement by the FWS.

But manatees aren't out of the woods yet, and are still considered a "threatened species." One reason for the status is that manatees reproduce very slowly — the time between generations is about 20 years. In addition, fishermen trawling with nets in the Amazon and West Africa pose a grave threat to these slow-moving mammals. Also, in West Africa, manatees are hunted for their meat.

Habitat loss from waterfront development also impacts their survival. Manatees are also vulnerable to collisions with speedboats.

Other facts

Manatees are thought to have evolved from four-legged land mammals more than 60 million years ago. Except for the Amazonian manatee, their paddlelike flippers have vestigial toenails — a remnant of the claws they had when they lived on land. The Amazon species name "inunguis" is Latin for "without nails."

The name manatee comes from the Taíno (a pre-Columbian people of the Caribbean) word manatí, meaning "breast."

Manatees' eyes are small, but their eyesight is good. They have a special membrane that can be drawn across the eyeball for protection. Their hearing is good too, despite not having outer ear structures, because manatees have large inner ear bones.

Manatees' only teeth are called marching molars. Throughout a manatee's life, the molars are constantly replaced — an adaption to their diet of abrasive vegetation.

Manatees have only six neck vertebrae. Most other mammals, including giraffes, have seven. As a result, manatees cannot turn their heads sideways, and must turn their whole body around to look behind them.

Algae, photosynthetic organisms, often grow on manatees' skin.

Manatees never go on land.

Manatees don't always need to breathe. As they swim, they poke their nose up above the water's surface to catch a few breaths every few minutes. If they are simply resting, they can stay under the water for 15 minutes without taking a breath, according to National Geographic.

An animal that is similar to the manatee is the dugong (Dugong dugon). Dugongs are also in the order Sirenia, but they are in a different family, Dugongidae. These manatee cousins are found in the Indian and Pacific oceans. They have a notch in their tails, as well as tusks.

Manatees and dugongs may have inspired mermaid legends. In ancient mythology, sirens were monsters or sea nymphs who sang mesmerizing songs that lured sailors to steer their ships onto treacherous rocks. After a long sea voyage, sailors may have thought they were seeing sirens, or mermaids, when they were probably seeing manatees or dugongs.

Additional resources

• The USGS Sirenia Project conducts long-term, detailed studies of the West Indian manatee.
• The Florida Manatee Program can tell you where to see manatees and provides a boater's guide to avoid collisions.
• At Save the Manatee Club, you can "adopt" a real manatee. Donations help fund manatee conservation."