Manatees

Common Name: Manatees

Class: Mammalia

Order: Cetacea

Family: Delphinidae

Genus: Trichechus

Species: Three species

     West Indian manatee  Trichechus manatus

     Amazonian manatee  Trichechus inunguis

 West African manatee  Trichechus senegalensis

West Indian manatee  Trichechus manatus

Taxonomy/Description

Manatees belong to the family, Trichechidae, of the Mammalian Order Sirenia.  Sirens were mythological beings of the ocean that lured sailors to their deaths with beautiful singing.  Manatees and dugongs are supposed to have given rise to the mermaid legend, hence their designation in the order Sirenia.  This order also includes the dugong.  One may distinguish manatees from the dugong by its tail.  A dugong's tail is shaped like that of a dolphin.  A semicircular or crescent shape.  Manatees have a rounder, fully circular tail.

West Indian manatee  Trichechus manatus

Despite the manatee's aquatic appearance, it is not closely related to whales, dolphins, seals, or sea lions.  In fact, their closest relatives are elephants and hyraxes.  Like elephants and hyraxes, they are herbivorous.  Manatees also have vestigial toe nails on their flippers.  Sirenians are the only extant herbivorous marine mammals.  One hundred pounds of vegetation may be consumed daily, due to the low nutritional value of the plant life.  Manatees are hindgut fermenters, not ruminants.  A thick bristly upper lip is the manatee's most apparent feature.  This lip is split down the center, and each half can be moved individually to grasp vegetation.

Genus:  Trichechus

The generic name Trichechus and the family name Trichechidae are both derived from the Greek words trikhos, meaning "hair", and ekho, meaning "I have".  This refers to the bristly hair on the mouths of the manatee species.

West Indian or Caribbean manatee Trichechus manatus

The specific name, manatus, is Latin for "manatee".  Adult West Indian manatees grow to about 15ft in length and reach weights of 1600lbs.  West Indian manatees are found in estuaries and swamps along the Gulf Coast of North America.  This includes the southeastern United States as well as most of Central America.  Manatees are also found along the shores and lagoons of some Caribbean Islands, like Haiti.  They are observed as far north as Virginia in the summer, and as far west as Louisiana.  During the winter season manatees migrate in warm Floridian waters.  West Indian manatees graze on seagrasses of the ocean floor.  Their mouth has evolved at a very adaptive angle to account for this grazing.  Their forelimbs are occasionally used to uproot plants from the ocean bottom as well.

West Indian manatee  Trichechus manatus

Amazonian manatee Trichechus inunguis

The specific name, inunguis, is Latin for "nailess", referring to the lack of toenails on this species' flippers.  The Amazonian manatee's range extends throughout the Amazon River Basin. The flooded forests during the rainy season provide the manatee with large amounts of foliage and vegetation.  Amazonian manatees do not graze on seagrasses of the ocean floor like its larger cousin, the West Indian manatee.  Instead this species relies mainly on surface plants and overhanging shoreline vegetation.  Aquatic grasses and overhanging vegetation in flooded forests are the main components this animal's diet. 

West African manatee Trichechus senegalensis

The specific name, senegalensis, means "belonging to Senegal", referring to the manatee's west African range, including the nation of Senegal.  The West African manatee's range extends along the western coast of Africa.  Estuaries and coastal lagoons as far north as Senegal and as far south as Angola.  Some animals live in freshwater rivers as far inland as Niger.  The brackish water of mangrove swamps is this species preferred habitat.  This manatee does not graze on seagrasses of the ocean floor like its New World counterpart, the West Indian manatee, Trichechus manatus.  Instead this species relies mainly on surface plants and overhanging shoreline vegetation.  Adult West African manatees grow to 10-13ft in length and reach weights of 1100lbs.  This species is externally indistinguishable from the West Indian manatee.

Reproduction/Behavior

Social hierarchies are not observed among manatees.  Territories are also not evident.  A female and calf exhibit strong bonds, but no social bonds exist between adults.  Loose congregations are common around resources.  Juvenile males will group together before they reach breeding age.  Small family groups are occasionally sighted.  Once males sexually mature at about 9-10 years, they will mate with available females.  Large breeding herds form each year.  Males engage in disorganized pushing and shoving to establish a breeding rights.  Females reach sexual maturity at 4-5 years, usually breeding at 7-9 years of age.  The gestation period is 12-14 months, with calves being born every 3-5 years.

West Indian manatee  Trichechus manatus

Conservation

West African manatee populations are declining for a variety of reasons.  Despite local laws, people still hunt the manatee for meat and oil.  Fishing nets, trawls and canal locks can accidentally drown manatees as well.  Even large boat propellers can kill manatees.  The destruction of mangrove trees for firewood decreases the available habitat space for the manatee.  Large populations of this species still do exist, but the population is declining.

West Indian manatee  Trichechus manatus

The development of waterfront property is a large hazard to the West Indian manatee's habitat.  Less space is available for wild manatees, and more human pollutants and artifacts enter the region.  Fortunately, a variety of laws and regulations have been passed to protect this species in the American states bordering the Gulf of Mexico.  Marked boating lanes restrict boaters from entering known manatee habitats.  A major threat to manatees in modern times has been watercraft collisions.  Boat propellers often cause injury or death to a haplessly swimming manatee.  Deep scars and cuts marking the bodies of some manatees are reminders of this threat.  Ingestion of foreign objects also harm manatees.  Manatees may eat fishing line and hooks while they forage along the ocean bottom.  A slow reproductive rate makes manatees especially vulnerable to extinction.

West Indian manatee  Trichechus manatus

Amazonian manatees are hunted by South American natives for meat.  The destruction of rainforest trees for industry, farmland and urban development also affects manatees.  The soil erosion of from forest destruction depredates the manatees' food supplies.  Fishing nets and trawls accidentally drown manatees.  Protection of South American rainforests of the Amazon River Basin will conserve the Amazonian manatee.

 

Content provided by Canisius College students under the direction of Michael Noonan, PhD.