95.
West African Manatee
(Trichechus senegalensis)
VU
Overview
The West African manatee is the least well-known of the three manatee species. It is thought to be similar in appearance and behaviour to the better-known West Indian manatee. Like its relatives, this gentle manatee is threatened with extinction as a result of human activities. The principle threat is incidental catch in fishing equipment, although the species is also hunted in some regions either because it is considered a pest or for its meat and body parts. Habitat loss and degradation caused by the destruction of mangroves and damming of waterways is also a threat. Fewer than 15,000 individuals are thought to survive, with some populations already thought to have been driven to the brink of extinction as a result of these threats.
Urgent Conservation Actions
The existing laws to protect manatees require enforcement throughout this species’ range.
Distribution
Trichechus senegalensis occurs in most of the coastal waters, brackish estuaries, and adjacent rivers along the coast of West Africa from southern Mauritania to …
Media from ARKive
ARKive image - African manatee
ARKive image - African manatee
Evolutionary Distinctiveness
Order: Sirenia
Family: Trichechidae
The sirenians (manatees and dugongs) are more closely related to elephants than to marine mammals such as whales and dolphins. They belong to an ancient radiation of African mammals known as the Afrotheria. This superorder includes seven groups of animals thought to have shared a common ancestor around 100 million years ago. These animals have little superficial resemblance to each other. Together with the sirenians and elephants, this group also includes the aardvark, hyraxes, sengis (or elephant-shrews), golden moles and tenrecs.

Sirenians are conventionally divided into four families: two, the Prorastomidae and the Protosirenidae, are extinct and known only from the Eocene, while the Dugongidae (dugongs, including Steller’s sea cow) and Trichechidae (manatees) survive today.

The fossil record of the Sirenia extends over 50 million years. The sirenians are thought to have branched off from the Proboscidea (elephants) during the Palaeocene, and quickly dispersed to the New World. The earliest known representative of the group was a pig-sized prorastomid from Jamaica from the early Eocene. This four-legged animal could walk on land, but probably spent much of its time in water. It had an extremely dense skeleton, which acted like ballast to keep the animal submerged in shallow waters. By the middle Eocene, protosirenid sea cows were abundant in North America, Europe and Asia. While the early sirenians had narrow snouts that suggested selective browsing, the muzzles had by this time broadened and became more downturned to ‘mow’ the carpets of seagrass on the ocean floor. The Dugongidae first appeared in the mid-late Eocene of the Mediterranean region. It was among these forms that the loss of the functional hind limbs took place. The manatees (Trichechidae) are the dugong’s closest living relatives. They are thought to have diverged from the Dugongidae at some time between the late Eocene and mid Oligocene.

There are three species of manatee alive today: the West Indian manatee, Trichechus manatus; the South American manatee, Trichechus inunguis; and the West African manatee, Trichechus senegalensis.
Description
Size: 
Head and body length: 3-4 m
Weight: Less than 500 kg
Adult West African manatees are greyish brown in colour whereas newborns are born with darker colouration that fades after approximately one month until it is similar to that of an adults.  The body of a manatee is seal-shaped, tapering to a flat paddle-shaped tail. Fine colourless hair covers the entire body and there are stout bristles around the mouth. The head is broad with a short snout and small eyes with no eyelashes and small ears.
Ecology
Less is known about the West African manatee than its relative the West Indian manatee. In island regions the West African manatee is usually found as solitary individuals or as small family groups but groups of up to 15 individuals have been sighted. Along the coast and further inland along tributaries the West African manatee is less commonly found in groups. Feeding and moving mostly during the night, West African manatees rest during the day in water that is 1-2m deep, often using mangroves or other vegetations as cover. Their diet consists of aquatic vegetation from overhanging bank growth, mangroves or submerged aquatic plants. In some regions the West African Manatee is reported to eat fish from nets and rice from fields which brings them into conflict with the local human population.

Breeding is thought to occur year round and adult females will give birth to live young which can be up to 1m in length. Calves remain with their mothers while developing. This relationship is thought to be the only stable relationship between individuals. Since social behaviour is thought to be similar to that of the West Indian manatee it is likely that mating behaviour involves large groups of males following a fertile female competing with each other for mating access.
Habitat
The West African manatee seems to be restricted to water that is 18oC and over. It can be found in freshwater, brackish or salt water in a number of habitats such as marine coastal areas, lagoons, estuaries and river tributaries. Individuals show preference for mangrove habitats and calm water conditions.
Distribution
The West African manatee is found extensively along the west African coastline in a number of countries including Angola, Benin, Cameroon, Chad, Congo, Ivory Coast, Equatorial Guinea, Gabon; Gambia, Ghana; Guinea, Guinea-Bissau, Liberia; Mali, Mauritania, Nigeria, Senegal, Sierra Leone and Togo.
Population Estimate
Unknown. Surveys conducted in 1980-1981 produced a rough estimate of 9,000-15,000 individuals excluding Angola and Congo but it is likely that these numbers have since declined. More recent estimates from individual countries include 750-800 individuals from the Ivory Coast and 256 sightings (439 individuals) from Guinea Bissau. There is a lack of specific population information for most countries; however populations are thought to be most abundant in Gambia, Guinea Bissau and Gabon whilst numbers are in decline in Sierra Leona and near extinction in Senegal and possibly Benin, where for a time it was thought the local population was extinct.
Population Trend
Unknown.
Status
Classified as Vulnerable (VU A3cd; C1) on the 2010 IUCN Red List of Threatened Species.
Threats
The principle threat to manatees is incidental catch by fishing equipment. Although a number of fisherman report releasing live manatees from their fishing gear some are killed in the gear and it is not known what effect entrapment in fishing gear has on the manatee after it has been released. The West African manatee is also hunted for food and medicinal ingredients despite the fact that hunting of manatees is illegal. In Sierra Leon the West African manatee is considered a pest due to the damage it can do to rice fields and so the hunting of the manatee in response to this is another threat to the species.

Loss of habitat is also a threat to the West African manatee and destruction of mangroves and damming of water ways is leading to a decline in population numbers. An increasing threat is posed by increasing river traffic which is increasing the number of boat-manatee collisions, a problem that is already a significant threat to the closely related West Indian manatee in the United States.
Conservation Underway
The West African manatee is listed in CITES Appendix II which means the export of this species is strictly controlled. The hunting of the West African manatee is banned in all countries in which this species is found but enforcement of legislation related to this is limited. In regions where the manatee is not exploited this often due to human attitudes such as in Cameroon where perceptions that manatee meat is unpleasant to eat and dangerous to hunt, along with an awareness that it is illegal to hunt this species contribute to the conservation of this population. Conservation programmes are being initiated and set up in Senegal, Guinea-Bissau, the Ivory Coast, Nigeria and Cameroon with protected areas already in place in a number of countries.
Projects

The aim of this study is to significantly improve the knowledge of the ecology and health of the manatee in Cameroon through research, building local network with fishermen, partnering and engaging with private and state conservation organisations in order to develop and implement conservation strategies and policies for this species

Conservation Proposed
The existing legal protection needs to be enforced in all range states. Despite its protected status the West African manatee is still being hunted and protected areas are not being enforced sufficiently. Enforcement of legislation and higher fines for those caught selling manatee meat may help the conservation effort in areas where the sale of manatee meat is most common.
Associated EDGE Community members

Aristide works with West-African manatee in Cameroon

Links
References
Grigione, M.M. 1996. Observations on the the status and distribution of the West African manatee in Cameroon. Afr. J. Ecol. 34:189-195

Husar, S.L. 1978. Trichechus senegalensis. Mammalian Species. 89:1-3

Nowak, R.M. 1999. Walker’s mammals of the world. Volume 2. Johns Hopkins University Press, Baltimore and London. p992.

Powell, J. & Kouadio, A. 2008. Trichechus senegalensis. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4. <www.iucnredlist.org>. Downloaded on 15 November 2010.

Silva, M.A. and Araujo, A. 2001. Distribution and current status of the west African manatee (Trichechus senegalensis) in Guinea-Bissau. Mar Mammal Sci 17:2:418-424

Smithsonian Marine Station

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