|Scientific Name:||Trichechus senegalensis|
|Species Authority:||Link, 1795|
|Taxonomic Notes:||There are no recognized Trichechus senegalensis subspecies and limited genetic information indicates high genetic diversity (Vianna et al. 2005). Anecdotal assertions of morphological differences between isolated inland populations and coastal populations persists but there is no genetic or morphological evidence (Domning and Hayek 1986, Vianna et al. 2005).|
|Red List Category & Criteria:||Vulnerable A3cd; C1 ver 3.1|
|Assessor/s:||Powell, J. & Kouadio, A.|
|Reviewer/s:||Reynolds III, J.E. & Powell, J.A. (Sirenia Red List Authority)|
Criterion A3cd: This species is data limited with little new information since the previous assessment. Inference of a single generation time of up to 30 yrs in an unexploited population is based on data from the assessment for T. manatus latirostris. The level of threats, particularly hunting and incidental catches, appears to be continuing to increase throughout range with locally high rates and near extirpation in some regions. Lack of protein and continued poverty, and limited enforcement of national laws, are expected to drive increasing hunting levels. Destruction of coastal areas from mangrove harvesting, siltation and dams are resulting in reduced habitat. We estimate a high probability that a 30% or greater reduction in population size will result within a 90 year three generation period.
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.
|Range Description:||Countries of occurrence include: Angola, Benin, Cameroon, Chad, Congo, The Democratic Republic of the Congo, Côte d'Ivoire, Equatorial Guinea, Gabon, The Gambia, Ghana, Guinea, Guinea-Bissau, Liberia, Mali, Mauritania, Niger, Nigeria, Senegal, Sierra Leone and Togo. T. senegalensis occurs in most of the coastal marine waters, brackish estuaries, and adjacent rivers along the coast of West Africa from southern Mauritania (16°N) to the Loge, Dande, Bengo and Cuanza Rivers, Angola (18°S) (Beal 1939, Allen 1942, Blancou 1960, Robinson 1971, Husar 1978, Nishiwaki 1984, Grigione 1996, Powell 1996, Perrin 2001). They ascend most major rivers within their range until cataracts or shallow water prevents their progress. In some rivers, such as along the Benue River, manatees seek refuge during the dry season in permanent lakes that communicate with the rivers during high water but are cutoff when river waters subside (Sykes 1974). Manatees can be found 75 km offshore among the shallow coastal flats and mangrove creeks (with abundant seagrasses and calm water) of the Bijagos Archipelago of Guinea-Bissau (Powell 1990) as well as Casamance (Senegal). Isolated populations cutoff from the sea are found in Lake Volta, Ghana above the Volta hydroelectric dam. An additional population, essentially landlocked above the major rapids, is found in the upper reaches of Niger River in the inland delta of Mali as far as Segou, which are the furthest inland records, over 2,000 km from the ocean (Hatt 1934, Kienta 1982). Manatees are landlocked in the Logone and Chari Rivers of Chad (Hatt 1934, Salkind 1996). They occur along the entire length of the Gambia River, penetrating into Senegal where there are records as far upstream as Niokola Koba National Park (Grubb et al. 1998). In Chad, manatees are present in Lake Léré and Lake de Tréné along the Mayo-Kebbi, Bahr Keeta and Baningi rivers; manatees are also reported from the Baningi, Logone and Chari Rivers tributaries of Lake Chad. Sightings of manatees have been reported from Lake Chad but there are no documented records (Ita 1994). Centers of population appear to be Guinea-Bissau; the lagoons of Ivory Coast; the lower reaches of the Niger River, Nigeria; Sanaga River, Cameroon; coastal lagoons of Gabon and the lower reaches of the Congo River (Powell 1996). The manatee population in West Africa is reported to be reduced, but their present range appears to be comparable to historic reports (Husar 1978).
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.
Native:Angola (Angola); Benin; Cameroon; Chad; Congo; Congo, The Democratic Republic of the; Côte d'Ivoire; Equatorial Guinea; Gabon; Gambia; Ghana; Guinea; Guinea-Bissau; Liberia; Mali; Mauritania; Niger; Nigeria; Senegal; Sierra Leone; Togo
|FAO Marine Fishing Areas:||
Atlantic – eastern central; Atlantic – southeast
|Range Map:||Click here to open the map viewer and explore range.|
There are no population estimates based on qualitative information. Nishiwaki (1987) made a number of intuitive estimates for various areas. It is believed, however, that several local populations have been extirpated (Poche 1973, Wood 1937) though recent accounts of manatees from these regions have emerged (Powell pers. notes). T. senegalensis population decline has been largely attributed to hunting and incidental capture in fishing nets (Allen 1942, Cadenat 1957, Blancou 1960). Johnson (1937) reported that as many as 12 manatees a day were caught in a 100 mile stretch of the Gambia River. Powell (1984) estimated around two manatees a year were taken between 1978-1983 from this same area though this change cannot be attributed to less hunting pressure or reduced manatee numbers (or both). In Côte d’Ivoire, Powell (1996) sighted manatees on a daily basis, but also noted that manatee traps in the region were not uncommon. Two similar live traps set for research purposes caught five manatees in four days. Maigret (1982) and Powell (1985) speculated that habitat modification and the construction of dams would severely affect manatee numbers.
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.
|Habitat and Ecology:||
West and Central Africa contains a variety of suitable habitats for manatees ranging from large and small rivers, coastal estuaries, freshwater and saltwater lagoons, shallow quiet coastal bays, lakes and reservoirs. Like T. manatus, T. senegalensis inhabits practically every accessible habitat (Hartman 1979, Powell et al. 1981, Rathbun et al. 1983, Powell and Rathbun 1984). They were observed or recorded from coastal areas, estuarine lagoons, large rivers that range from brackish to fresh water, freshwater lakes and the extreme upper reaches of rivers above cataracts. In general, their habitat requirements seem to be similar to T. manatus and require sheltered water with access to food and freshwater (Powell and Rathbun 1984). They may transit areas of unsheltered coast, but they are usually rare in these areas.
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).
Manatees are exploited for their meat, skin, bones, and oil nearly everywhere they are found. They are trapped by various methods including nets, weirs, large box traps, drop traps using harpoons and snaglines (Powell 1996, Reeves et al. 1988, Roth and Waitkuwait 1986, Akoi 1992). In Guinea Bissau, Silva and Araújo (2001) reported 209 deaths between 1990–1998; of these, 72% died in fishing gear, 13% were hunted, 4% stranded at low tide and 11% the cause of death was undetermined. In Côte d’Ivoire, Powell (1996) found numerous large box traps situated around the rivers and lagoons from the Ghana border to Fresco. The 4x1 m traps are constructed of wooden poles stuck in the bottom and door weighted with a large rock. Powell (1996) built two of these box traps for catching manatees to radio tag; he caught five manatees in two of these traps over four days. Manatees are also caught in special nets with large mesh used specifically for manatees.
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).
West African manatees are listed in CITES Appendix II. Manatees are protected by national laws in all range states. Though West African manatees are protected throughout their range, enforcement and control of hunting appears negligible. Hunting is largely local and sometimes ritualized and the meat is usually consumed locally. In some regions, hunting is primarily opportunistic and meat and products are traded locally and across borders. Progress has been made in some regions to discourage hunting, but in general protection is minimal and offtake is likely at unsustainable levels. Availability of manatee meat in some markets has dropped, but it is not known whether this is due to increased protection or decreased abundance, probably the latter. Awareness of the protected status of the manatee is widespread in all areas surveyed, but there is little perceived fear of arrest and punishment (Powell 1996); enforcement is rare and fines or sentences for the most part have been negligible. Frequently when individuals have been arrested, the fine can be less than what is gained by selling the manatee meat and oil in the market (Powell 1996).
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.
|Citation:||Powell, J. & Kouadio, A. 2008. Trichechus senegalensis. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 09 December 2013.|
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