Trichechus senegalensis, Link, 1795

Russell A. Mittermeier & Don E. Wilson, 2014, Trichechidae, Handbook of the Mammals of the World – Volume 4 Sea Mammals, Barcelona: Lynx Edicions, pp. 548-562 : 561-562

2.

West African Manatee

Trichechus senegalensis

French: Lamantin dAfrique / German: Westafrika-Seekuh / Spanish: Manati de Africa Occidental

Other common names: African Manatee

Taxonomy. Trichechus senegalensis Link, 1795 ,

Senegal.

This species is monotypic.

Distribution. Coastal areas and large inland rivers of West Africa from the Senegal River at the Mauritania—Senegal border S to the Longa River in Angola.

They occur as far as 2000 km from the ocean in the Inner Niger Delta of Mali, up to 75 km off the continental shore in the shallows and mangrove creeks of the Bijagos Archipelago of Guinea-Bissau, and as far E as Lake Tréné in Chad; formerly in Lake Chad itself.

Descriptive notes. Total length up to 350 cm; weight 460 kg. Very little morphometric data are available for the West African Manatee, although 18 presumed adults measured in Ivory Coast averaged 260 cm in body length. The West African Manatee appears indistinguishable in external appearance from the West Indian Manatee (71. manatus ). Eyes appear to bulge outward more than in the West Indian Manatee or the Amazonian Manatee (7. inunguis ), but this trait has not been investigated thoroughly on an anatomical basis.

Habitat. Shallow coastal waters, estuaries and lagoons; mangrove swamps; flooded agricultural fields; and rivers as far inland as depths and rapids permit. Habitats used by the West African Manatee are comparable to those of the West Indian Manatee in their breadth. The West African Manatee is euryhaline, but it is unknown if it requires periodic access to freshwater. Relationships between temperature and limits to the distribution of the West African Manatee have not been well established, but a water temperature of 18°C has been suggested to be a lower limit of tolerance.

Food and Feeding. The West African Manatee eats plants from at least 38 genera, invertebrates, and fish from a diversity of aquatic habitats. Many more food plants are likely to be revealed in the diet with further study. Methods of feeding and anatomical specializations seem identical to those of the West Indian Manatee. In some areas, West African Manatees feed on cultivated grains and crops in flooded fields, and they can be regarded as agricultural pests. Feeding occurs primarily at night in areas with histories of hunting by humans.

Breeding. In some areas, the West African Manatee has been reported to mate when rainy-season water levels are rising, which may result in parturition and early lactation coinciding with periods of increased aquatic plant productivity. Births of singletons (c.100 cm in length) have been reported. Anecdotal accounts of groups of up to 15 individuals suggest mating herds, as in the West Indian Manatee, but there are no published details on breeding and reproduction of the West African Manatee.

Activity patterns. There is little information available for this species, but in Ivory Coast they are reported to feed for 4-6 hours daily, largely at night to avoid human hunters.

Movements, Home range and Social organization. There is little information available for this species, although some studies are underway. In Ivory Coast West African Manatees can move several kilometers between resting places and nocturnal feeding sites, which can be repeatedly used on successive nights. Seasonal movements occur in response to changing water levels in wet and dry seasons. West African Manatees are largely solitary but feeding and mating aggregations can occur. The breeding system involves an estrous female followed by mating herds of males similar to those better documented for West Indian Manatees.

Status and Conservation. CITES Appendix I. Classified as Vulnerable on The IUCN Red List. West African Manatees are protected by law in all nations in which they occur, but enforcement is sometimes lax, and exemptions occur for cultural purposes in some countries. The Nigerian government has allowed permits for killing of 1-2 manatees annually for a wrestling festival, and captures for symbolic uses also have been permitted in Niger. Illegal hunting can result in far more deaths, with an estimated total of over 2500 West African Manatees killed annually by poachers in Sierra Leone, Nigeria, and Cameroon combined. Many poaching methods are used in West Africa.

As examples, manatees are lured into box traps with cassava, speared from platforms on stilts, entangled in nets, shot by harpoons on baited triggers, and trapped by fences on outgoing tides. Many hunting and trapping practices for manatees are known throughout West Africa, and incidental capture in fishing nets is an additional major threat that in some areas has a greater impact than direct hunting. Deterioration and loss of habitat are increasing with rapid human population expansion in many West African countries. West African Manatees occur in areas of extreme human poverty, where food is scarce, and their economic value can reach US$ 400 in some areas. They are a source of aquatic bush meat and oil, which adds to the concern that their populations may be depleted. The Convention on Migratory Species includes a Memorandum of Understanding for the conservation of small cetaceans and manatees in West Africa, with signatories including 16 West African countries. Many indigenous cultures hold West African Manatees in high esteem, and manatees and their body parts are subjects of many traditional beliefs.

Bibliography. Allsopp (1969), Awobamise (2008), Dodman et al. (2008), Domning (1982), Domning & Hayek (1986), Grigione (1996), Husar (1978), Issa (2008), Keith & Collins (2007), Kouadio (2012), Marsh et al. (2011), Marshall et al. (2003), Moore, J.E. et al. (2010), Powell (1996), Reeves et al. (1988), Sikes (2010), Silva & Araujo (2001), Vianna etal. (2006).

Figures

1. West Indian Manatee (Trichechus manatus), 2. West African Manatee (Trichechus senegalensis), 3. Amazonian Manatee (Trichechus inunguus)

Distribution. Coastal areas and large inland rivers of West Africa from the Senegal River at the Mauritania—Senegal border S to the Longa River in Angola. They occur as far as 2000 km from the ocean in the Inner Niger Delta of Mali, up to 75 km off the continental shore in the shallows and mangrove creeks of the Bijagos Archipelago of Guinea-Bissau, and as far E as Lake Tréné in Chad; formerly in Lake Chad itself.