The West African Manatee, Trichechus Senegalensis

Introduction

Manatees are large aquatic mammals that feed exclusively on grass. They are found in coastal and inland waters on both sides of the Atlantic Ocean. The West African Manatee (Trichechus senegalensis) belongs to the Trichechidae family with order Sirenia (or sea cows). Other species of the order Sirenia are the South American manatee (Trichechus inunguis) and the West Indian Manatee (Trichechus manatus). All three manatees are classed as Vulnerable under the IUCN Red List of Threatened Species (IUCN Red List, 2007); Powell and Kouadio, 2008. Another Sirenian, Steller’s Sea Cow (Hydrodamalis gigas), lived in colder waters of the northern Pacific, but was hunted to extinction some 200 years ago. Of all species of Sirenians, the West African manatee is the least known biologically (Reynolds and Odell, 1991) and also the knowledge on its status in most of its geographic range is limited.

The West African manatee may reach up to 4.5 metres (14 feet 9 inches) in length and weighs about 360 kilograms (790 pounds). They can live for an estimated 30 years, with females bearing one calf (twins are rare) every three to five years.

Habitat and Distribution

The African Manatee occurs in rivers, estuaries, lagoons, and coastal regions of Western Africa, from southern Mauritania to the Cuanza and Longa Rivers, Angola (Husar, 1978; Nishiwaki et al., 1982) and inland as far as Mali, Niger and Chad. They have been 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, Gabon, Republic of the Congo, and Democratic Republic of the Congo (Silva and Araújo, 2001).

Population Abundance and Mortality

Although crocodiles and sharks occasionally kill manatees in Africa, the African Manatees main significant threats are from humankind, through activities such as poaching, habitat loss and other environmental impacts. Accidental capture in fishing nets, accidental collision with boats, the damming of rivers, cutting of mangroves for firewood, coastal modernization and destruction of wetlands for agricultural and other development are the West African manatee’s greatest threats (Powell, 1996; Akoi, 1992; Reeves et al., 1988). Coastal environmental wellbeing is critical in sustaining the African Manatee population.

This threat has been exacerbated over the years brought about also by local hunting for their palatable meat, their skin, bones and oil, causing significant population declines in certain areas (Husar, 1978). The reproductive biological characteristics (with one offspring per female in every 3 years) of this species render recovery of depleted stocks very slow.

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 (Silva and Araujo. 2001). More recent estimates from individual countries include 750-800 individuals from the Ivory Coast and 256 sightings (439 individuals) from Guinea Bissau (http://www.wcs.org/saving-wildlife/ocean-giants/west-african-manatee.aspx). 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.

Economic Importance

A study on the spatial distribution and exploitation status of the West African manatee in Sierra Leone was done by Reeves et al., in 1988. The study revealed that in addition to the above threats, the West African Manatee is considered as destructive pest in certain rice cultivated and fishing areas. The West African manatee feeds primarily on vegetation; it is dependent on emergent or overhanging, rather than submerged, vegetation.

They consume huge quantities of aquatic vegetation, which helps spread plant seeds and control plant overgrowth within their ecosystems. Their voracious feed behavior and movement in channels, estuaries etc. help reduce the obstacles or debris which in turn facilitates navigation and passage by users of water-ways for human economic activities. The manatee is hunted in its entire distribution areas for its meat, skin, oil, etc. (Powell. 1996; Reeves et al., 1988) providing source of protein and other benefits.

Management

The West African manatee is listed in CITES (2007) which means trade in this species is regulated. Accordingly, 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 most African countries there are regulations to protect and conserve marine mammals in their natural environments. These laws are somewhat blanket in nature for marine mammals such as manatee, cetaceans (Dolphins, Whales), and etc. Specific considerations such as Action Plan and legal framework for manatee protection and conservation are lacking. In addition, public awareness in respect to conservation issues for manatee is either inadequate or non-existent as well, 1996; Reeves et al., 1988).

Proposed Options for Conservation and Stock Restoration

1. Consultative forum to increase public awareness on manatee conservation, mitigation plan and identification of key stakeholders such as hunters, traders, farmers tec.
2. Establish spatial distribution, mapping main occurrence sites and current population status
3. Develop and implement a data collection to monitor occurrence, distribution, studies on population biology and ecology
4. Formulation of specific legislative clauses for conservation at national and regional levels

Bibliography

1. Akoi, K. 1992. Education et sensibilisation des populations pour la conservation du lamantin ouest africain (Trichechus senegalensis) en Côte d’Ivoire. Wildlife Conservation Society, 31pp.
2. CITES (2007): http://www.cites.org
3. Dagou, M. and Greatrix, E.( 2007), Conservation Prospects for the West African Manatee, retrieved January 8, 2011
4. Grigione, M.M. 1996. Observations on the status and distribution of the West African manatee in Cameroon. Afr. J. Ecol. 34:189-195
5. Husar, S.L. 1978. Trichechus senegalensis. American Society of Mammalogists, Mammalian Species 89: 1-3.
6. Manatee conservation in Sierra Leone (2009). MFMR- SLG and PRCM-IUCN project.
7. Nishiwaki, M., M. Yamaguchi, S. Shokita, S. Uchida and T. Kataoka. 1982. Recent survey on the distribution of the African manatee. Scientific Reports of the Whales Research Institute 34: 137-147.
8. Nowak, R.M. 1999. Walker’s mammals of the world. Volume 2. Johns Hopkins University Press, Baltimore and London. p992.
9. Powell J.A. 1996. The Distribution and Biology of the West African Manatee (Trichechus senegalensis Link,1795).United Nations Environmental Program, Regional Seas Program, Oceans and Coastal Areas, Nairobi, Kenya. 68p.
10. Powell, J. & Kouadio, A. 2008. Trichechus senegalensis. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4. . Downloaded on 15 November 2010.
11. Reeves, R.R., Tuboku-Metzger, D. & Kapindi, R.A. 1988. Distribution and exploitation of manatees in Sierra Leone. Oryx 22:75-84.
12. Reynolds, J.E. III and D.K. Odell. 1991. Manatees and dugongs. Facts on File, New York. 192pp.
13. Silva, M.A. and Araújo, A. (2001) Distribution and current status of the West African manatee (Trichechus senegalensis) in Guinea-Bissau. Marine Mammal Science, 17(2): 418 - 424.
14. Tatarinov A. C. (2011). Это моя страница на Викискладе. Моя страница на РуВики: ru:Участник: 

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