The East African manatee according to MammalMAP
Meet the West African manatee (Trichechus senegalensis). A cousin of the dugong, manatees are found along the West African coastline between Angola and Senegal, inhabiting coastal waters and rivers. They are comfortable in both salt and fresh water, but seem to prefer shallow estuaries and swamps. These mega-herbivores feed on huge quantities of aquatic plants – up to 8000 kg/year – so much so that some have proposed that this exceptional feeding ability makes them perfect for the job of Specialised Aquatic Weed Eaters! As with many African mammals, humans are their worst enemy and greatest threat. Illegal hunting of manatees for their palatable meat, and for their skin, bones and oil has led to significant declines in numbers in some areas. Manatees sometimes also become accidentally entangled in fishing nets, which compromises their survival, even if they escape. Perhaps worse still is that – because fishing nets may get damaged when manatees are accidentally entrapped – fisherman in some areas conduct manatee hunts to prevent net damage. Manatees also clash with people when, during the rainy season, they roam on land and destroy crops. For all of these reasons, manatees are now listed as Vulnerable on CITES, and their populations need to be carefully monitored, managed and protected. For more information go to the MammalMAP virtual museum or blog.
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.
Biogeographic Regions: ethiopian (Native ); atlantic ocean (Native )
MAJOR LAKES: Volta, Inland delta Mali, Lake Léré, Lake de Tréné.
MAJOR RIVERS: (N to S) includes lakes within these river systems, the Senegal, Saloum, Gambia, Casamance, Cahacheu, Rio Mansoa, Rio Geba, Rio Grande de Bulba, Rio Tombali, Rio Cacine, Kogon, Kondoure, Sierra Leone, Great Scarcies, Little Scarcies, Sherbro, Malem, Waanje, Sewa, Missunado, Cavally, St. Paul, Morro, St. John, Bandama, Niouniourou, Sassandra, Comoe, Bia, Tano, Volta, Mono, Oueme, Niger, Mekrou, Benue, Cross, Pie, Katsena Ala, Deb, Okigb, Issa, Bani, Akwayafe, Rio del Rey, Ngosso, Andokat, Mene, Munaya, Wouri, Sanaga, Faro, Chari, Bamaingui, Bahr-Kieta, Logoné, Mitémélé, Gabon, Ogoué, Lovanzi, Kouliou, Congo, Loge, Dande, Bengo, and Cuanza.
West Coast of Africa from Senegal R. to Cuanza R
Other Physical Features: endothermic ; bilateral symmetry
Catalog Number: USNM A20907
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Mammals
Preparation: Skull; Skeleton
Collector(s): P. Du Chaillu
Locality: Gabon River, mouth (see Gray 1865:134), Gabon, Africa
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).
Habitat Regions: tropical ; saltwater or marine ; freshwater
Aquatic Biomes: rivers and streams; coastal ; brackish water
Other Habitat Features: estuarine
Habitat and Ecology
Optimal coastal habitats for manatees, based on the movements of radio-tagged manatees in Côte d’Ivoire and the number of reported sightings from other areas were: a. coastal lagoons with abundant growth of mangrove or emergent herbaceous growth; b. estuarine areas of larger rivers with abundant mangrove (Rhizophora racemosa) in the lower reaches and lined with grasses, particularly Vossia and Echinochloa further upriver; c. shallow (<3 m depth) and protected coastal areas with fringing mangroves or marine macrophytes, particularly Ruppia, Halodule or Cymodocea. In riverine habitats that have major fluctuations in flow rates and water levels, manatees seem to prefer those areas that have access to deep pools or connecting lakes for refuge during the dry season and seasonally flood into swamps or forests with abundant grasses and sedges, particularly Vossia, Echinochloa and Phragmites.
T. senegalensis are mostly solitary, with mothers and calves the principal social unit. Manatees will often rest together in loose, small groups of two to six individuals. They feed principally at night and travel in the late afternoon and at night. They usually rest during the day in water that is 1–2 m deep and sometimes in the middle of a watercourse or hidden in mangrove roots or under natant vegetation. They make little disturbance while swimming. These latter behaviors may be due to hunting pressures.
Manatees feed primarily on vegetation including: Vossia sp., Eichornia crassipes, Polygonum sp., Cymodocea nodosa, Ceratophyllum demersum, Azolla sp., Echinochloa sp., Lemna sp., Myriophyllum sp., Pistia stratioties, Rhizophora racemsoa, and Halodule sp. In Senegal (Powell, unpub. data) and Sierra Leone (Reeves et al. 1988), manatees are also known to eat small fish captured in fishermen’s nets. In Senegal and The Gambia, shell remains of mollusks have also been found in their stomachs.
Manatees can travel freely from salt to freshwater. They appear to prefer estuarine areas where there is little disturbance and the waters are shallow and calm. They can be found in marine habitats where there are relatively calm water and a source of freshwater. For example, in Senegal, The Gambia, and Guinea-Bissau, manatees are attracted to freshwater seeps or springs that are found in marine habitats (Powell 1990).
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).
Life History and Behavior
Perception Channels: tactile ; chemical
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
IUCN Red List of Threatened Species: vulnerable
IUCN Red List Assessment
Red List Category
Red List Criteria
Criterion C1: Using survey information from Côte d'Ivoire, Guinea-Bissau, The Gambia, portions of Senegal and Cameroon, and inferring what is known about manatee habitat in other range states and manatee density data for T. manatus, it is estimated that there are fewer than 10,000 manatees in West Africa. A population decline of at least 10% is anticipated based on continuing and increasing anthropogenic threats.
- 2006Vulnerable(IUCN 2006)
- 1994Vulnerable(Groombridge 1994)
- 1990Vulnerable(IUCN 1990)
- 1988Vulnerable(IUCN Conservation Monitoring Centre 1988)
- 1986Vulnerable(IUCN Conservation Monitoring Centre 1986)
Date Listed: 10/16/1979
Lead Region: Foreign (Region 10)
Where Listed: Entire
Population location: Entire
Listing status: T
For most current information and documents related to the conservation status and management of Trichechus senegalensis , see its USFWS Species Profile
The following adapted from Perrin (2001):
The species occurs in the Senegal River and its tributaries (Powell, 1996); this river forms the border between Mauretania and Senegal. It is an infrequent inhabitant of the Diawlang Reserve, a wetland reserve of interconnecting streams, lakes and ponds.
In Senegal, the manatee is close to extinction (Navaza and Burnham, 1998). In most areas of the country, it has not been seen for many years. There are a few remaining in the Casamance River in the estuary and up to Kolda, and there have been some reported sightings in the delta of the Sine Saloum River near Kaolack, but the species is considered to be severely depleted and threatened. In the Casamance River where they still occur, they are respected and not molested, so there is some hope they can be saved there.
In the Gambia, numbers are thought to have declined, but as of 1993 the manatee was still numerous in the River Gambia. They have been fully protected for many years but in the 1980s were still hunted extensively.
Guinea-Bissau at one time was considered to be one of the last sanctuaries of the manatee, because of the relatively undisturbed state of its mangroves, wetlands and river systems (Schumann 1995, Powell 1996). Silva and Araújo (2001) found that manatee occupied a wide variety of habitats and were most abundant around the Bijagos Archipelago. Based on interviews, a total of 256 sightings involving 439 individuals interviewed were reported. Powell (1996) reported seeing about 20 individual sternum from manatees hunted in the Bijagos Archipelago by a single Senegalese fishermen who seasonally fished there. In 1997, the government signed an agreement with IUCN to develop a National Plan for Conservation of the West African Manatee in Guinea-Bissau, and some training and survey work started, but the work stopped when the war started in 1998 (Silva and Araújo, 2001). The major source of mortality before the war was accidental capture in fishing nets; they were not extensively hunted. Silva and Araújo (2001) reported 209 manatees killed between 1990-1998, 24.8/yr. Most recently, manatees have been advertised for export on the internet, and two were exported to the Toba Aquarium in Japan (Asano and Sakamoto 1997, Kataoka et al. 2000, Anon., 2000b).
Little information is available on the manatee in Guinea. The country has extensive suitable habitat, and the species is known to occur in the area (Powell 1996), but no systematic studies have been carried out (Barnett and Prangley 1997).
In Sierra Leone the manatee is also declining (Reeves et al. 1988, Powell 1996). It is protected but widely hunted and marketed, because it is good to eat and because it is thought to be a pest by rice growers and fishermen among the Mende People. The manatee in the late 1980s was still widely distributed in the country, but the catches at that time were thought to be unsustainable. The animals are trapped, netted and harpooned. There is some concern about the effect of modern fishing gear on the manatee, because it is easily tangled in monofilament gillnets.
Manatees occur throughout the major rivers of Liberia, including in the proposed national park of Cestos-Sankwer, and in the Piso Lake region (Powell 1996). No information is available on status.
Côte d'Ivoire (Ivory Coast)
In the Côte d'Ivoire, the manatee by the mid-1980s had been reduced by hunting to 5 or 6 small isolated populations, with an estimated total number of less than 750 animals. Hunting is illegal, but it still continued in the late 1980s, with traps, harpoons, hook lines, baited hooks and nets (Roth and Waitkuwait 1986, Nicole et al. 1994, Powell 1996). A program of research and education began in 1986, sponsored by the Wildlife Conservation Society. The population is tentatively estimated at 750–800 (Akoi Kouadio pers. comm., 2000). Illegal hunting is still a problem, as is habitat destruction by barrages. However, some success has been enjoyed in educating potential hunters and in enforcing the hunting ban in some areas, with the aid of Wildlife Conservation International (Akoi 2000, Anon, undated). A conservation plan is in development (Akoi 2000).
Recent surveys by the Institute of Aquatic Biology confirmed the continued existence of manatees in Volta Lake and Digya National Park; additional surveys are planned (Powell 1996). Hunting continues.
Manatees may still exist in Togo Lake (Powell 1996). No information is available on status.
In Benin, the manatee had been thought to be extinct. However, this is apparently not the case (Powell 1996), and a new research and conservation project on the species is underway to establish its current distribution and numbers as well as gather data on its ecology and behavior (Risch 2000).
The manatee is found throughout Nigeria but is depleted, due to hunting (Powell 1996). It is hunted for its oil. There is no effective enforcement of protection laws. The most recent concern is about pollution of the Niger Delta by oil development.
In Cameroon, based on a survey sponsored by WWF-USA and the Wildlife Conservation Society in 1989 (Grigione 1996), manatees may still be numerous in some areas. Illegal hunting has been very limited, due mainly to local attitudes toward the species rather than legal protection, but poaching from across the border in Nigeria is a severe problem. Habitat destruction by dams is also a problem.
There is no recent information on manatees; they likely occur in the lower reaches of the Mitémélé River on the mainland (Powell 1996).
Gabon may have one of the highest densities of manatees remaining in Africa (Powell 1996). Reports of opportunistic sightings are common. Bycatch occurs in gillnets.
A preliminary survey in 1994 found manatees in lakes, rivers and lagoons of Congo (Powell 1996).
Republic of Congo (former Zaire)
Manatees were once common in the extreme lower reaches of the Congo River below Binda (Powell 1996). A local name for the species exists in the upper reaches of the Congo, so it may occur there as well. Status is unknown.
Manatees have been reported from the entire coast, but little information is available on abundance or status (Powell 1996).
Manatees are found throughout the entire Niger River system of Mali (Powell 1996) but may have been reduced by hunting. Hunting continues but may be decreasing, as meat now only rarely appears in the markets; it is not clear whether this is due to legal protection, less demand for the meat, or greatly decreased abundance.
The species has been recorded from the Niger River below Niger in Nigeria and above Niger in Mali, so it can be assumed that it occurs in the Niger River in Niger as well, but there is no information on its distribution or status (Powell 1996). It may also occur in the Niger portion of the Chad basin.
Manatees were once abundant in the Chad basin but had become rare by 1924 (Powell 1996). In a survey in 1995, they were found to be less abundant than formerly but not uncommon in Lére and Tréne Lakes in the Mayo-Kebbi region. Hunting continues on the rivers and lakes, despite enforcement efforts. The animals are sought mainly for their oil, which is shipped with dried meat to Cameroon.
Manatees inhabit all of the nations that surround Burkina Faso (Mali, Ivory Coast, Ghana, Togo, Benin and Niger). They are present in Volta Lake above the dam (see Ghana above). However, Perrin (2001) could find no mention of its occurrence in the upper tributaries of the Volta (White Volta, Red Volta and Black Volta) or in the Mekrou River, which forms the boundary between Burkina Faso and Togo/Benin and drains the wetlands of the Parc National de l'Arly. Pending directed surveys, its occurrence there must be considered possible.
Incidental killing of manatees occurs in many areas around West and Central Africa. Cadenat (1957) recorded the deaths of five manatees around Joal, Senegal in nets used for catching sharks. Manatees are occasionally killed in fishing trawls. In Côte d’Ivoire, stationary funnel nets are placed across the inlets of major rivers to catch shrimp swept past on tidal currents. These are strong nets that have a wide mouth that faces upstream and then narrows down to a small bag on the cod end. The tidal currents where they are usually set are often strong and several of these nets can block the entire channel. Between 1986 and 1988, three manatees were killed in the vicinity of Grand Lahou by drowning in these nets, including one radio tagged manatee (Powell 1996). Akoi (1992) describes how manatees in Côte d’Ivoire and probably elsewhere are sometimes caught in fishing weirs made of sticks. These weirs are common in Côte d’Ivoire and in many other areas in Africa.
Recent threats include loss of habitat due to damming of rivers, cutting of mangroves for firewood and destruction of wetlands for agricultural development. At Kanji dam on the Niger River, Nigeria and on the Volta River, Ghana, manatees have been known to be killed in the turbines and intake of the hydro-electric generator (Powell, 1996). In Nigeria, for example, Isahaya (pers. comm.) reported seeing as many as six manatee carcasses at one time below the Kainjii dam, Nigeria.
In Senegal and The Gambia, increases in salinity and change in waterflow due to damming can cause manatees to strand or vacate an area with unknown demographic results (Powell 1996). Natural droughts and tidal changes are known to strand manatees (Dupuy and Maigret 1978, Powell 1996, Silva and Araújo 2001).
Coastal development near Abidjan, Côte d’Ivoire resulted in loss of habitat and increased human disturbance contributing to the disappearance of manatees in the area. Increased large vessel traffic in some of the rivers and lagoons may also pose a threat from collisions with watercraft, the highest known cause of death in Florida and Belizian manatee populations.
The manatee is fully protected in all of the nations in which it occurs. Due to remoteness and lack of enforcement, manatees are taken for food and traditional medicinal products throughout their range (Powell 1996). Manatee meat is openly sold in local markets. In Cameroon, manatee meat was sold along the roadside near Douala and could easily be spotted from a passing car. Manatee meat was seen on three out of five visits during a three month period (Powell pers. obs.). Little historical data exists to indicate a decrease in catch rates. For example, at one point in the 1930s as many as 12 manatees a day were caught in a 100-mile stretch of the Gambia River. Based on interviews, Powell (1996) determine that only two per year were taken in the same area between 1978-83. Manatee meat and oil is reported to move illegally in trade between Chad and Cameroon (Powell 1996). In Mali, Senegal, and Chad, manatee oil is more prized than the meat. The oil is used for its reputed medicinal properties to cure rheumatism and to condition the skin and hair (Kienta 1982, Reeves et al. 1988). Oil from the head is used to treat ear infections. In Mali and along the Benue River, certain cuts of the meat are considered to have particular useful properties. For example, the parts of the penis are used to cure impotency in men, and the skin can be made into whips (Kienta 1982, Powell 1996). In Sierra Leone, villagers consume all parts of the manatee carcass except for the heavy ribs (Reeves et al. 1988). The meat is shared among villagers and any remains are sold by the trapper. The bones are used to make handles for walking sticks or spinning-tops used in a local game called cii.
National and international trade in live manatees exists. In Nigeria manatees are taken for exhibit in local zoos. In 1996, a Japanese aquarium acquired two manatees for exhibit from Guinea-Bissau (Asano and Sakamoto 1997). Wild caught manatees from Guinea-Bissau are offered for sale on the internet (River Zoo Farms, ttp://www.riverzoofarm.com/manatee.htm).
Efforts are being increased to protect manatees from local sale. In Senegal, there has been a long effort to initiate a research and conservation project for manatees in the Senegal River, particularly Lake Guier. There is interest in a captive breeding program at the Djoudj National Park (Powell 1990). In Guinea-Bissau, recommendations have been made for the protection of manatees (Silva and Araújo 2001). Côte d’Ivoire has one of the most important manatee conservation programs. A manatee awareness and conservation program has been in place since 1989 (Akoi 1992). On Lake Volta, surveys of manatees have been conducted and recommendations made for their conservation (Ofori-Danson 1995). In Nigeria, Pandam Lake was designated a manatee sanctuary (Sykes 1974). In Cameroon, Lake Ossa has been proposed as a protected area for manatees and the government is strongly interested in having a research and conservation project started there. In Gabon, the Gambas protected area may be one of the most important for manatees in Africa and there is strong interest in developing a conservation program to protect manatees in the N’Dogo Lagoon complex (MAB 2000).
List of protected areas in western Africa where Trichechus senegalensis is known to occur.
Ivory Coast - Azagny National Park; Ivory Coast - Iles Eotiles National Park; Cameroon - Reserve de Faune de Douala-Edea; Congo - Reserve de Faune de Conkouati; Gabon - Reserve de Faune et Domaines de Chasse de Sette; Nigeria - Kainji Lake National Park; Cameroon - Korup National Park; Gambia - Baboon Island National Park; Gambia - Kiangs West National Park; Mauritania - Diaouling Strict Nature Reserve; Nigeria - Kainji Lake National Park; Nigeria - Pandam Wildlife Park; Nigeria - Obudu Game Reserve; Senegal - Parc National de Basse Casamance; Senegal - Delta du Saloum; Senegal - Parc National des Oiseaux de Djoudj; Senegal - Santuaire Ornithologique de la Pointe de Kalissaye; Ghana - Digya National Park.
Relevance to Humans and Ecosystems
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).
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).
The African manatee (Trichechus senegalensis) is a species of manatee and is the least studied of the four species of Sirenians. Photos of African manatees are very rare; although very little is known about this species, scientists think they are similar to the West Indian manatees. They are found in coastal marine and estuarine habitats and in fresh water river systems along the west coast of Africa from the Senegal River south to the Kwanza River in Angola, including areas in Gambia, Liberia, Guinea-Bissau, Guinea, Sierra Leone, Côte d'Ivoire, Ghana, Mali, Nigeria, Cameroon, Chad, Gabon, Republic of the Congo, and Democratic Republic of the Congo. Although crocodiles and sharks occasionally kill manatees in Africa, their only significant threats are from humankind, such as poaching, habitat loss, and other environmental impacts.
They live as far upstream the Niger River as S gou, Mali. Although rare, they occasionally get stranded as the river dries up at the end of rainy season and are cooked for a meal. The name in Songhai, the local language, is "ayyu". A landlocked colony of manatees also lives in Lake Lere in southwestern Chad near the Cameroonian border something of an anomaly given that the lake is hundreds of miles inland and not connected to the sea in any way.
Manatees roam the Urasi River in the Okija-Ihiala-Oguta area between Anambra and Imo States of Nigeria. These animals are normally in the area between July through November when the Urazi River is heavily flooded. It is believed that they roam from the Oguta Lake in Oguta, Imo State downstream to the River Niger in Onitsha, Anambra State upstream. Sometimes, they run aground and are killed for meat by local people. They are also hunted for the meat, although the Nigerian Government is believed to have outlawed killing the animals. Locally, in Okija, manatees are called "Emei.'
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