Trichechus senegalensisAfrican manatee

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Geographic Range

Trichechus senegalensis occurs along the west coast of Africa. The Senegal River marks the northern limit of their range while the Cuanza River of Angola serves as the southern boundary.

Habitat

Trichechus senegalensis are found in shallow coastal wasters and freshwater rivers. They appear to prefer large, shallow estuaries and weedy swamps, and have been reported to avoid salt water (Nowak 1991 and Nishiwaki 1984). Their range is limited by temperature. They are rarely found in waters of less than 18 degrees celsius (Nowak 1991).

Physical Description

Reproduction

Trichechus senegalensis is a poorly studied species, and much of the information about their behavior and reproduction has been inferred based on their close similarity to the very well studied Trichechus manatus. They are capable of reproducing throughout the year; however, a peak in calving tends to occur in late spring or early summer (CMC 1997). Females are sexually mature as early as three years of age. A female in estrus is joined by a dozen or more males. Together they form a mating group in which copulation appears to occur at random (Save the Manatee Club 1997). Gestation lasts about 13 months and usually a single calf is born at a time, but twins do occur occasionally. Calves are born tail first, and they can swim on their own (CMC 1997). They feed from a pair of pectoral mammary glands. Trichechus senegalensis are believed to live to about 30 years of age, and females can bear young every three to five years (Sikes 1974 and CMC 1997).

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • sexual

Behavior

Again, the behavior of this species is poorly studied. They are believed to be at least partially nocturnal, as this is when most hunters successfully take manatees (Sikes 1974). Trichechus senegalensis may live singly or in family groups of up to four to six individuals (Nowak 1991). They have few natural predators, and perhaps as a result they do not have a very sophisticated social system. The strongest bond between individuals occurs between a mother and her calf. Calves may remain dependent on their mothers for up to two years (Save the Manatee Club 1997).

Communication and Perception

Food Habits

Trichechus senegalensis feeds primarily on aquatic vegetation, and adults may consume up to 8000kg per year. They may also feed on overhanging bank growth, and populations living in estuarine environments are reported to feed exclusively on mangroves (Nowak 1991). In many areas, local fishermen claim that Trichechus senegalensis are responsible for stealing fish from nets. However, this behavior has yet to be confirmed (Reeves et. al. 1988). Trichechus senegalensis are dependent upon microorganisms living in their large intestines to aid in the digestion of certain plant materials (Rathbun 1990).

Economic Importance for Humans: Positive

Villagers in Sierra Leone and Nigeria hunt Trichechus senegalensis for their meat (Reeves et. al. 1988). They have developed elaborate means of trapping the animals which they eventually kill with harpoons or guns (Sikes 1974 and Robinson 1971). In contrast to this, villagers in Cameroon have a different perception of Trichechus senegalensis. They do not like the taste of the meat and they believe that Trichechus senegalensis are fierce animals that become violent when attacked. Nigerian fishermen are often responsible for the poaching of Trichechus senegalensis in Cameroon (Grigione 1996). It has also been reported that the skin of Trichechus senegalensis has medicinal and therapeutic properties (Reeeves et. al. 1988).

Economic Importance for Humans: Negative

Villagers in Sierra Leone consider Trichechus senegalensis a major pest of rice crops. Fishermen believe these animals are responsible for removing fish from nets, but this is unconfirmed (Reeves et. al. 1988).

Conservation Status

Other Comments

Trichechus senegalensis are the source of many myths and legends. They have often been mistaken for mermaids. The blubber is believed to have curative powers and possession of body parts, especially the skull and teeth, is believed to confer special status in many aspects of life, including sports, politics, and academics (Sikes 1974).

They are known in West Africa as "dikunge" and "peixe-muhler".

Contributors

Ethan Kane (author), University of Michigan-Ann Arbor.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

brackish water

areas with salty water, usually in coastal marshes and estuaries.

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

estuarine

an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

freshwater

mainly lives in water that is not salty.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

References

Center for Marine Conservation. 1997. Manatees and Dugongs. http:// www.cmc-ocean.org./22231m2_manatee.html

Grigione, M. M. 1996. Observations on the Status and Distribution of the West African Manatee in Cameroon. African Journal of Ecology, 34:189-195.

Nishiwaki, M. 1984. Current Status of the African Manatee. Acta Zoologica Fennica, 172:135-136.

Nowak, R. M. 1991. Walker's Mammals of the World. Fifth Edition. Johns Hopkins University Press, Baltimore.

Rathbun, G. B. 1990. Manatees. Grzimek's Encyclopedia of Mammals. McGraw-Hill, New York.

Reeves, R. R., D. Tuboku-Metzger, and R. A. Kapindi. 1988. Distribution and Exploitation of Manatees in Sierra Leone. Oryx, 22:75-84.

Robinson, P. T. 1971. Wildlife Trends in Liberia and Sierra Leone. Oryx, 11:117-122.

Save the Manatee Club. 1997. Membership Handbook. Maitland, Florida.

Sikes, S. 1974. How to Save the Mermaids. Oryx, 12:465-470.