Journal of Marine Science: Research & Development
Open Access

The West African Manatee (Trichechus senegalensis ), is an herbivorous aquatic mammal in the order of Sirenia. Its presumed distribution covers regions from Mauritania to the Cuanza River in Angola, as well as in the river systems of Cameroon, Chad, Gabon, Niger, Mali and Burkina Faso. The species has never been studied before across its entire range although it is also listed as “Vulnerable” in the IUCN Red List of Threatened Animals Anonym, 1999 [1]. And appears on Appendix I of CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora) since 2013 [2].

As in many developing African states, very few conservation efforts are oriented toward marine mammals in Cameroon. Recent surveys have demonstrated that manatees are present in Cameroonian coastal areas; however, these vulnerable species are being threatened by hunting, by-catches and habitat degradation [3-6]. However, there is no system for monitoring and quantifying these threats and how they population affect this specie in Cameroon. Having very limited information about their current distribution and abundance, it becomes difficult to understand population dynamics, local status and trends.

This current study could help to present information on status of manatee in Cameroon coastline and enforce the process of his gazetment as national marine parks. The exercise was aimed at contributing to the compilation of information on status of the specie and also better understanding of this endangered species in Cameroon. The objectives of the survey were:

- To assess the abundance and distribution of this specie;

- To identify human impacts and manatees-human conflicts;

- To sensitive local population for the conservation of this aquatic mammal.

Scope of study

The coastal zone of Cameroon stretches over 402 km Sayer et al. [7], from the Nigerian border in north (Akwayafe river, latitude 4˚40’ N) to the Equatorial Guinean border in the South (Campo river, latitude 2˚20’N). In terms of longitude, it is located between 8˚15’E and 9˚30’E) (Figure 1).

Figure 1: The Cameroon coastal zone (CWCS) [8].

The continental shelf is about 10600 km² and gradually descends through 30, 50 and 100 m depths [9,10]. The rainfall is ordinary heavy on the coast with average at 3000-4000 mm with the peat of 10160 mm yearly at Debunscha around Mount Cameroon. The temperature is always high with average at 25°C. The main characteristic of the hydrology in the Cameroon coast is the permanent existence of a warm, low salinity surface layer cold, high salinity bottom layer [11]. The warm surface layer is 20-30 m thick and is separated from the bottom layer by a permanent thermocline whose position fluctuates with season and location considered effect of current systems, the rainfall as well as the important water discharge from numerous coastal rivers.

Data collection

The survey of West African Manatee was carried out in major inland wetland areas along Rivers Dipoumbe, Mouha, Nsah, Sanaga and Lake Tissongo in Douala Edea Wildlife Reserve, Lake Ossa in Reserve of Lake Ossa and Lake Bodiman around Nkam River. This work was done through a collaborative management system with local people set up since 1997 by local NGO Cameroon Wildlife Conservation Society (CWCS) and CAMB (Cameroon Marine Biology Association).

The survey was based on direct observation on the field and questionnaire carried out along fishing camps.

Also, several services and libraries in Universities were visited to compile information available in various sites from reports and thesis.

General threats

Although laws and conservation policy exist on this threatened species in Cameroon, it is facing many threats. By-catches in gillnets and other fishing gears and the potential of increasing direct takes may be the most severe and cause of significant mortality. Other threats of varying magnitude of concern include: habitat encroachment through coastal development (e.g. port and road construction), over-fishing, chemical and acoustic pollution, ship collisions and ghost nets. The almost complete lack of scientific data on the biology, distribution, stock structure and abundance of sea turtles and cetaceans in Cameroon waters has as detrimental result that the impact of these threats cannot be properly evaluated, let alone addressed. An acceleration of research is urged with the involvement of national universities. More faunal surveys are needed to unveil the potentials of the reserve and the need for the establishment of important relationships between species abundance, site temporal conditions (sandbank disappearance) and socio-economic activities with the view of identifying sustainable wetland ecosystem utilisation options.

Destruction of habitats: Habitat destruction is the main threat to manatee through deforestation by cutting firewood and work around fisheries along the coast, the extension of agro-industries and various pollution related to the use of pesticides and other fertilizers around Lake Ossa in Dizangue (Littoral Region). We can also talk of urbanization by expanding coastal cities and the mining and quarrying of sand.

Poaching: Poaching through illegal hunting is still a threat axes of this species despite legislation and numerous conservation measures for this species. In many sites there is still an activity of illegal hunting of this species around Douala-Edea Wildlife Reserve and Cameroon Estuary (Figure 2).

Figure 2: Fishing net for manatee poaching [14].

Ayissi [5] reported 34 individuals caught yearly in Douala-Edea Wildlife Reserve. According to Ayissi and Jeff et al. [12,13] around 292 were caught incidentally per year in gillnet along Cameroon Coastline, 18 individuals were caught in the space of three weeks in Yassoukou hamlet by one hunter and actually 5 to 6 individuals are caught monthly during raining season around Mouanko in Douala-Edea Wildlife Reserve.

Unwanted catches: Unwanted catches are also a threat to this species through net frame it is the vehicle most used in various fisheries. Despite the herbivorous nature of the case according to information from many fishermen would take the case often comes when taking the fish in nets to consume about 292 individuals are taken annually [12,13].

Desertification and climate change: The drying of various aquatic environments, especially in the inland areas in lakes and along some rivers through the advancement of the desert and especially climate change greatly reduces these vulnerable habitats around Lake Tissongo and surrounding rivers.

Site specific threats

Ntem Estuary on the border Equatorial Guine: Water pollution: Unwanted catches: They were noted in this area through fishing nets because fishing is the main socio-economic activity in the area.

Cameroon Estuary

The water pollution: Through the discharge of pollutants from the oil companies and factories of the area as ALUCAM Breweries, the Port of Douala, Douala Airport, cement and many solid and liquid wastes from households in this area the habitat of this species suffers much destruction. One of the most affected aquatic ecosystems is Lake Ossa, through pollution; SAFACAM causes eutrophication of the ecosystem. This area is subject to a decade of boom in oil exploration with many potential releases without prior indication of threats to this species.

Poaching: The manatee meat is common in many restaurants mainly in the cities of Edea, Douala, Mouanko. These animals are taken with the Harpoon, nets, traps and others. According to Ayissi [5], 18 individuals were captured in Canton Yassoukou in the Sanaga Maritime in three weeks. Also one of the major centers of capture of this species in the upper reaches of the river NkamYabassi in Lake Bodiman.

Unwanted catches: One of the greatest threats to this species in the area is accidental capture in fishing nets through the lagoons, lakes and associated as Lake Ossa, Tissongo Lake, Lake Nsah, rivers Sanaga, Nyongand Dipombe rivers and streams (Mouaha and Kombe). According to Takoukam [15] around 4-6 Mouanko individuals are taken monthly in major rainy seasons i.e. between June and October.

Deforestation: Deforestation in this area through the use of firewood from mangroves for smoking fish in fisheries and expansion of agribusiness as SOCAPALM (Cameroon Society of Palm Oil), SAFACAM (Palm and rubber agro-industries farms) according Din et al. [16] 500000 m3/an fuel wood and service are taken to the city of Douala. And according to Ajonina [17] the period between 1985 and 2010 there was an almost complete disappearance of 20% to 25% of mangrove forests in Estuary Cameroon, mainly through the rapid urbanization of the city of Douala (Douala Districts 1, 2 and Douala 4 districts), siltation and sedimentation (Borough of Dizangue). The impact of these samples is little known because no evidence exists for damage assessment.

The water pollution: Through the discharge of pollutants from oil companies and factories of the area as SONARA (oil company), CDC (Cameroon Development Corporation), PAMOL (Palm and rubber agro-industries farms) and many solid and liquid waste from households in this area. This area is subject to a decade of boom in oil exploration with many potential releases without prior indication of threats to this species.

Poaching: Hunting manatee is common in the area and according to Grigione [3], there exists across border traffic with neighbouring Nigeria in this area, but there is no indication on the same traffic and catch data are lacking.

Unwanted catches: As in all areas of use of the net as fishing gear, by-catch are common in the waters of Ndian, Granny, Cross River and numerous creeks but information about the threat is non-existent.

Deforestation: Deforestation in this area through the use of firewood from mangroves for smoking fish in fisheries and expansion of agribusiness as CDC (Cameroon Development Corporation) PAMOL (Palm and rubber agro-industries farms) and implementing much infrastructure development in this area since the postwar Bakassi, but any figures exist.

The West African Manatee occurs commonly in coastal and estuarine habitats, coastal lagoons and the lower reaches of most rivers systems from Campo in Ntem River in Equatorial Guinea border to Bakassi peninsula along Cameroon coastline. The population of this specie was substantially diminished during last years by water pollution with wastes from surrounding towns as Douala, Edea and Limbe, illegal poaching, unwanted catches by fishing nets, deforestation of mangrove and revering Atlantic forests through urbanization and agriculture. Also, international and national laws are relatively ineffective due to difficulties with enforcement in the country.

Manatee by-catch was ubiquitous across study areas but rare on Cameroon coastline, where hundreds of West African manatees are killed each year through a combination of by-catch and intentional harvest. Manatee by-catch occurred almost exclusively in gillnets (but was also reported for hook-line gear in Cameroon). However, direct harvest of West African manatee-via use of nets, traps, and harpoonsis common in certain sites.

For conservation of this species following measures will be taken in various ways:

- Further research in critical sites to assess populations.

- Study of migration flows.

- Evaluation of all impacts especially from poaching, pollution of various kinds and destruction of critical habitat.

- Study of the composition of populations.

Policy, legal and institutional framework

- Sign the MoU emergency for small cetaceans and Sirenian Western Atlantic.

- Create marine protected sanctuaries for this species in its area of distribution areas.

- Encourage a national policy for conservation of the species.

- Train young Cameroonian on the biology of the specie.

Habitat restoration

- Restore all mangroves degraded habitats all along the coast.

- Assess the impact studies of different projects on the coast and

- Encourage a national policy for conservation of the species.

- Train young Cameroonian on the biology of the specie.

Habitat restoration

- Restore all mangroves degraded habitats all along the coast.

- Assess the impact studies of different projects on the coast and involve the conservation of manatees in the management plans.

- Manage efficiently the waste on the Cameroon coast.

- Educate and sensitize masses.

Thanks are due to all who were involved in this survey particularly the field staff from CWCS (Cameroon Wildlife Conservation Society) of Douala-Edea Wildlife Reserve, other NGO as CAMB (Cameroon Association of Marine Biology), local people from Yassoukou, Malimba and Bodiman. The boat pilot Timba Martin from Mouanko.