Trichechus Senegalensis Research Articles

The genome of African manatee Trichechus senegalensis reveals secondary adaptation to the aquatic environment

Sirenians exhibit unique aquatic adaptations, showcasing both convergent adaptive features shared with cetaceans and unique characteristics such as cold sensitivity and dense bones. Here, we report a chromosome-level genome of the African manatee (Trichechus senegalensis) with high continuity, completeness, and accuracy. We found that genes associated with osteopetrosis have undergone positive selection (CSF1R and LRRK1) or pseudogenized (FAM111A and IGSF23) in the African manatee, potentially contributing to the dense bone formation. The loss of KCNK18 may have increased their sensitivity to cold water temperatures. Moreover, we identified convergent evolutionary signatures in 392 genes among fully aquatic mammals, primarily enriched in skin or skeletal system development and circadian rhythm, which contributed to the transition from terrestrial to fully aquatic lifestyles. The African manatee currently possesses a small effective population size and low genome-wide heterozygosity. Overall, our study provides genetic resources for understanding the evolutionary characteristics and conservation efforts of this species.

The African Manatee (Trichechus Senegalensis, link 1795) in the Ramsar site of Setté Cama: Case at Lake Cachimba

The West African manatee (Trichechus senegalensis) is classified as vulnerable on the IUCN red list and is highly protected in Gabon. Gabon could be home to one of the highest densities of manatees remaining in Africa. Many people agree on the presence of manatee populations in several lakes and lagoons in Gabon. The aim of this study is to investigate the distribution and abundance of manatees by monitoring. The study was carried out in the catchment area of Lake Cachimba at the Setté Cama Ramsar site. We used three data collection methods: secondary data collection, boat surveys and surveys of markets and landing sites. Data analysis was based on descriptive statistics, manatee encounter rates and carcass encounter rates (number of carcasses/km of river). The chi-square (χ2) goodness-of-fit test was used to determine whether there were significant differences in the abundance of manatee encounter rates between Lake Cachimba and the Mbissi River. The results showed that manatee hotspots in Lake Cachimba are located near the mouth of the DuebiRiver, along the shore of the village of Cachimba. In addition, fishing activities are a potential threat to the African manatee.

Acoustic methods improve the detection of the endangered African manatee

The African manatee (Trichechus senegalensis) is an elusive, data-deficient, and endangered species which inhabits marine and freshwater systems throughout Western and Central Africa. A major challenge in understanding the species ecology and distribution is the difficulty in detecting it using traditional visual surveys. The recent invasion of Giant Salvinia (Salvinia molesta) at the most important site for the species in Cameroon further limits their detectability and may restrict their movements and habitat use. To investigate methods’ effectiveness in detecting African manatees, we conducted monthly vessel surveys from which visual point scans, 360° sonar scans, and passive acoustic monitoring were conducted simultaneously at ten locations and over 12 months in Lake Ossa, Cameroon. Manatee detection frequency was calculated for each method and the influence of some environmental conditions on the methods’ effectiveness and manatee detection likelihood was assessed by fitting a binary logistic regression to our data. Detection frequencies were significantly different between methods (p < 0.01) with passive acoustics being the most successful (24.17%; n = 120), followed by the 360° sonar scan (11.67%; n = 120), and the visual point scan (3.33%; n = 120). The likelihood of detecting manatees in Lake Ossa was significantly influenced by water depth (p = 0.02) and transparency (p < 0.01). It was more likely to detect manatees in shallower water depths and higher water transparency. Passive acoustic detections were more effective in uninvaded areas of the Lake. We recommend using passive acoustics to enhance African manatee detections in future surveys.

Using transfer learning with a convolutional neural network to detect African manatee (Trichechus senegalensis) vocalizations.

African manatees (Trichechus senegalensis) are vulnerable, understudied, and difficult to detect. Areas where African manatees are found were acoustically sampled and deep learning techniques were used to develop the first African manatee vocalization detector. A transfer learning approach was used to develop a convolutional neural network (CNN) using a pretrained CNN (GoogLeNet). The network was highly successful, even when applied to recordings collected from a different location. Vocal detections were more common at night and tended to occur within less than 2 min of one another.

Observations on the feeding activities of the West African Manatee, Trichechus senegalensis Link, 1795 in a semi-wild environment

The presence of the West African manatee, Trichechus senegalensis in a semi-wild holding facility in Little Stream Farm, Ibesikpo Asutan Local Government Area, presented an opportunity to study directly, aspects of their biology, which hitherto were little known. This study was conducted to identify their plant food preferences and feeding behaviour as a reflection of what may approximate their activities in the wild. The selected plants were weighed (wet weight in kg) with spring balance in batches of 3kg per plant species and offered in batches to the manatee for a specified period (initially for 24 hours, then 4 hours and 10 hours). Of the 15 plant species presented, Emilia sonchifolia, Commelina diffusa, Nymphaea sp., Panicum laxum, Eleusine indica and Rhynchosia sp. had high preference levels while the quantity of Chromolaena sp. consumption was minimal. Bambusa sp., Heliotropium indicum, Ludwigia abyssinica and Hyptis lanceolata were ignored by the animal on repeated presentations. Studies on day-time and night-time feeding showed little difference in quantities of food consumed. However, the maximum consumption of 7kg was observed at daytime feeding on day 4 of the 14 days trial. The result showed that in the event of West African manatee rescue and fostering in temporary holding facilities, these plants’ checklists may come in handy as food materials. They may also come for important considerations as plants whose natural growth and propagation should be encouraged in areas designated for West African manatee conservation.

Diet composition of the African manatee: Spatial and temporal variation within the Sanaga River Watershed, Cameroon.

The present study aimed to investigate the diet of African manatees in Cameroon to better inform conservation decisions within protected areas. A large knowledge gap on diet and seasonal changes in forage availability limits the ability to develop informed local management plans for the African manatee in much of its range. This research took place in the Sanaga River Watershed, which includes two protected areas in the Littoral Region of Cameroon: the Douala‐Edea National Park and the Lake Ossa Wildlife Reserve. We analyzed 113 manatee fecal samples and surveyed shoreline emergent and submerged vegetation within the Sanaga River Watershed. We used microhistological analyses to determine the relative contribution of each plant species to African manatee diets and compared across locations and across seasons (wet vs. dry season). We found that the shoreline vegetation is diverse with over 160 plant species, unevenly distributed across space and season, and dominated by emergent vegetation mostly represented by the antelope grass (Echinochloa pyramidalis). We recorded a total of 36 plant species from fecal samples with a spatial and temporal distribution mostly reflecting that of the corresponding shoreline vegetation. African manatees appear to be primarily opportunistically feeding on available vegetation across the seasons and habitat. This work documents the current, but changing, state of plant availability in the Sanaga River Watershed and reports the African manatee diet in Cameroon for the first time. This information can play a critical role in successfully managing the species and these protected areas. If we wish to protect the African manatee and the aquatic ecosystems within the Sanaga River Watershed, we must understand how forage availability changes over time, especially as its waters become nutrient enriched, eutrophic, and exposed to invasive species of plants in a changing world.

African manatee (Trichechus senegalensis) habitat suitability at Lake Ossa, Cameroon, using trophic state models and predictions of submerged aquatic vegetation.

The present study aims at investigating the past and current trophic status of Lake Ossa and evaluating its potential impact on African manatee health. Lake Ossa is known as a refuge for the threatened African manatees in Cameroon. Little information exists on the water quality and health of the ecosystem as reflected by its chemical and biological characteristics. Aquatic biotic and abiotic parameters including water clarity, nitrogen, phosphorous, and chlorophyll concentrations were measured monthly during four months at each of 18 water sampling stations evenly distributed across the lake. These parameters were then compared with historical values obtained from the literature to examine the dynamic trophic state of Lake Ossa. Results indicate that Lake Ossa's trophic state parameters doubled in only three decades (from 1985 to 2016), moving from a mesotrophic to a eutrophic state. The decreasing nutrient gradient moving from the mouth of the lake (in the south) to the north indicates that the flow of the adjacent Sanaga River is the primary source of nutrient input. Further analysis suggests that the poor transparency of the lake is not associated with chlorophyll concentrations but rather with the suspended sediments brought‐in by the Sanaga River. Consequently, our model demonstrated that despite nutrient enrichment, less than 5% of the lake bottom surface sustained submerged aquatic vegetation. Thus, shoreline emergent vegetation is the primary food available for the local manatee population. During the dry season, water recedes drastically and disconnects from the dominant shoreline emergent vegetation, decreasing accessibility for manatees. The current study revealed major environmental concerns (eutrophication and sedimentation) that may negatively impact habitat quality for manatees. The information from the results will be key for the development of the management plan of the lake and its manatee population. Efficient land use and water management across the entire watershed may be necessary to mitigate such issues.

First characterization of vocalizations and passive acoustic monitoring of the vulnerable African manatee (Trichechus senegalensis).

Even among the understudied sirenians, African manatees (Trichechus senegalensis) are a poorly understood, elusive, and vulnerable species that is difficult to detect. We used passive acoustic monitoring in the first effort to acoustically detect African manatees and provide the first characterization of their vocalizations. Within two 3-day periods at Lake Ossa, Cameroon, at least 3367 individual African manatee vocalizations were detected such that most vocalizations were detected in the middle of the night and at dusk. Call characteristics such as fundamental frequency, duration, harmonics, subharmonics, and emphasized band were characterized for 289 high-quality tonal vocalizations with a minimum signal-to-noise ratio of 4.5 dB. African manatee vocalizations have a fundamental frequency of 4.65 ± 0.700 kHz (mean ± SD), duration of 0.181 ± 0.069 s, 97% contained harmonics, 21% contained subharmonics, and 27% had an emphasized band other than the fundamental frequency. Altogether, the structure of African manatee vocalizations is similar to other manatee species. We suggest utilizing passive acoustic monitoring to fill in the gaps in understanding the distribution and biology of African manatees.

The evolutionary history of manatees told by their mitogenomes

The manatee family encompasses three extant congeneric species: Trichechus senegalensis (African manatee), T. inunguis (Amazonian manatee), and T. manatus (West Indian manatee). The fossil record for manatees is scant, and few phylogenetic studies have focused on their evolutionary history. We use full mitogenomes of all extant manatee species to infer the divergence dates and biogeographical histories of these species and the effect of natural selection on their mitogenomes. The complete mitochondrial genomes of T. inunguis (16,851 bp), T. senegalensis (16,882 bp), and T. manatus (16,882 bp), comprise 13 protein-coding genes, 2 ribosomal RNA genes (rRNA - 12S and 16S), and 22 transfer RNA genes (tRNA), and (D-loop/CR). Our analyses show that the first split within Trichechus occurred during the Late Miocene (posterior mean 6.56 Ma and 95% HPD 3.81–10.66 Ma), followed by a diversification event in the Plio-Pleistocene (posterior mean 1.34 Ma, 95% HPD 0.1–4.23) in the clade composed by T. inunguis and T. manatus; T. senegalensis is the sister group of this clade with higher support values (pp > 0.90). The branch-site test identified positive selection on T. inunguis in the 181st position of the ND4 amino acid gene (LRT = 6.06, p = 0.0069, BEB posterior probability = 0.96). The ND4 gene encodes one subunit of the NADH dehydrogenase complex, part of the oxidative phosphorylation machinery. In conclusion, our results provide novel insight into the evolutionary history of the Trichechidae during the Late Miocene, which was influenced by geological events, such as Amazon Basin formation.

First Satellite Tracking of the African Manatee (Trichechus senegalensis) and Movement Patterns in the Senegal River

First Satellite Tracking of the African Manatee (Trichechus senegalensis) and Movement Patterns in the Senegal River

Some Physico-chemical Properties of the Habitat of West African Manatee Trichichus senegalensis along River Benue, Nigeria.

Some physico-Chemical parameters of Manatee habitat along river Benue were conducted. The river was divided into four segments; Makurdi, Abinsi, Gbajimba and Gbaji. In each srgment, ten (10) sample points were chosen and the following parameters ; Temperature, dissolved solid (D0), pH, Total dissolved solid,(TDS) Electrical conductivity (EC) and Biological oxygen demand (BOD) were measured. Data collected was subjected to statistical analysis. The result indicated that there were significant differences in the pH, Electrical conductivity, and Biological oxygen demand (BOD) among the four study areas. The mean pH ranged between 6.94 to 7.09, EC ranged between 47.76 µs/cm -55.91 µs/, dissolved oxygen was between 15.82Mg/L in Makurdi to 18.50Mg/L in Abinsi, mean Temperature moved between 29.27oC in Makurdi to 34.33oC in Gbaji, the total dissolved solids ranged from 44.46 Mg/l in Abinsi to 56.74Mg/L in Gbajimba while Biological Oxygen demand (BOD) was least at Gbajimba( 3.03 Mg/L) and Makurdi with 5.49Mg/L It is therefore suggested that continuous monitoring of the water health of the river be sustained for the survival of the west African manatee.

Socio-Economic Aspect of African Manatee (Trichechus Senegalensis) Hunting and Capturing in Parts of Ogun and Ondo State, Southwest Nigeria

This research was carried out to understand the emerging practice of hunting, capturing and trading of African manatee (Trichechus senegalensis) by fishermen and hunters in Iwopin lagoon area of Ogun State and some parts of Ondo State, Southwest Nigeria. The African Manatee has been declared an endangered species under IUCN red list. This research was conducted over one year to understand the period and factors influencing fishermen to hunt, capture and culture the animals in fish pond enclosure. The study deploys and employed immersion survey approach with enumerators staying with the fishermen in the survey communities. Analysis of the survey indicated that 70% of manatee hunters are adults in the age range of 31-60.55% of respondents use traditional traps to capture manatee and 43% uses drag fishing net (Ifatiko). The study further reveals that while 30% of the hunters captures manatee and keep it alive in fish ponds to sell it alive to buyers, 28% do so to sought for parts of its body particularly the oil and bones for medicinal purposes. Of the total 100 respondents, 21% opined that training fishing group on alternative livelihoods will help to promote conservation of the endangered sea creature, 20% suggested liaising with conservation agents on the need to train fishermen on how to rear manatee in its natural habitat. Alternative livelihood strategies and community conservation practices is recommended for the fishermen/hunters in order to prevent the practice of illegal capture and trade of Manatee.

Water Parameters and Floristic Composition of African Manatee <i>(Trichechus senegalensis)</i> Habitat in Pandam Wildlife Park, Nigeria

The study of the physicochemical characteristic and floristic composition of African manatee habitat in Pandam Lake was conducted between 2012 and 2013. The water parameters were tested using standard method while line intercept method was adopted for vegetation survey. Data obtained on the water parameters were analyzed using one-way ANOVA. Plant species diversity index was analyzed using PAST Software. The mean seasonal water surface area increase was 66.12±5.01. The mean water depth in the dry season was 2.28±1.14 while the wet season value was 4.3±1.15. Also the mean water transparency was for wet and dry seasons were 64.02±4.66 and 111.18±4.26 respectively. The mean pH value was 6.5±0.14. Water salinity ranges from 0.00mg/l to 0.01mg/l, mean DO was 6.24±1.13, nitrate was 0.08±0.02 and mean conductivity of 52.65 ±2.12. A total of 42 plant species from 23 families were recorded in Pandam Lake. The family Poaceae had the highest number of species (22) (30.56%). The grass species had the highest frequency of 13 while trees recorded the lowest (3). Also there are more perennial species (n=28; 66.67%) than annual species (n=14; 33.33%). The Shannon diversity index was 3.72. Thirteen species of plants recorded in Pandan Lake during this study were known to provide food for manatees across their range in Africa. All the water parameter values were within the range tolerable by manatee. The Lake have diverse species of plants that manatee can feed on both in the wet and dry seasons. The park management should maintain the integrity of the ecosystem by regulating fishing and other human activities to avoid pollution. The park should be taken over by the Federal government for effective protection of the resources most especially manatee.Keywords: Water quality, vegetation, African manatee, Pandam Lake

Occurrence patterns of African manatees, conflicts with humans, and local perception in the Southern Korup Area, Cameroon

Abstract The African manatee has been poorly studied throughout its range and is heavily hunted. This study aimed at discerning patterns in manatee sightings and emerging conflicts with humans, as well as the local perception of manatees, outside the southern periphery of Korup National Park, Cameroon. The study investigated whether patterns in manatee sightings and manatee‐related conflicts differ between aquatic systems in southern Korup, and which demographic variables determine perceptions of the manatee in the study area. For this purpose, the study used a three‐stage stratified random sampling design with a structured questionnaire to survey 101 local fishers. The reported patterns of manatee sightings and manatee‐related conflicts were as follows: in the Nyangorobe River during the wet season only, where crop raiding and net destruction by manatees were reported; in the Ndian River and the mangrove estuary only during the dry season, where fish theft and net damage were reported; and in the Moko River during both seasons, where crop raiding, fish theft, and net destruction were reported. Reducing these conflicts is likely to increase local support for the conservation of manatees, because fishermen kill them in response to net destruction and fish loss. Most reported sightings were at waterway intersections and river bends, suggesting that waterway connectivity is important to manatees for dispersal, foraging, and escape from danger. The log‐odds probability of negative perception decreased significantly with awareness of manatee protected status but increased with age and primary or higher education level. These findings have implications for community outreach focused on raising awareness of the importance of manatee conservation by schoolchildren and the public.

Ecology and characterization of the habitat of the West African manatee (Trichechus senegalensis) in Niger

Ecology and characterization of the habitat of the West African manatee (Trichechus senegalensis) in Niger

West African Manatee Trichechus senegalensis (LINK, 1795) in the Estuary of the Congo River (Democratic Republic of the Congo): Review and Update

The West African manatee Trichechus senegalensis (LINK, 1795) is the least studied Sirenian species, with both old and fragmentary literature on the population in the Congo River estuary. In the Democratic Republic of the Congo, T. senegalensis occurs up to 60 km upstream around Boma town, a zone under partial protection of the Marine Mangrove Park. In order to develop efficient conservation actions, there is an urgent need to revise the state of knowledge on the species in the Congolese part of its distribution range. This paper reviews the current status and distribution of T. senegalensis populations in the Congo River estuary based on geolocated observations (N=33), and provides a summary of local communities’ knowledge, attitude and practices of the manatees ’ecosystem services (e.g.: river dredging, touristic potential). The reported potential threats-poaching, habitat loss, risk of genetic drift-show that the T. senegalensis population of the Congo River estuary is in danger and that its survival requires specific conservation measures.

Surveys of mammal communities in a system of five forest reserves suggest an ongoing biotic homogenization process for the Niger Delta (Nigeria)

Community composition and an index of relative abundance were analyzed for mammals (excluding most rodents, shrews and bats) of five forest reserves in the Niger Delta (Southern Nigeria). Twenty-nine species were recorded, 86.2% of them being found in all protected areas. Although most of the species were already known from the study area, there were unexpected patterns concerning the duikers. Indeed, the presence of only one species (Philantomba walteri) (CH Smith, 1827) was confirmed, whereas at least five additional duiker species were reported for the study area by earlier authorities. Another duiker species (Cephalophus niger Gray, 1846) was recorded once during the present surveys and is not known whether it represents a stabilized presence in the Niger Delta. The empirical Abundance Index suggested that only three species were very rare (Trichechus senegalensis (Link, 1795), C. niger, and Pan troglodytes (Blumenbach, 1775)). Diversity-dominance diagrams showed that the evenness profiles were simila...

The Behavioural and Morphometric Features of West African Manatee: Trichechus senegalensis in a Semi-Wild Environment

The behavioural and morphometric features of West Africa manatee; Trichechus senegalensis, in a semi-wild environment was study from July1st 2008 to November 30th 2008. Surface water was measured to determine the Physico-chemical parameters of the stream. Mean values of surface water temperature of 26.56 ± 1.08oC; pH, 6.47 ± 0.25; Free carbon dioxide, 8.83 ± 1.44 mg/L; total alkalinity, 10.35 ± 1.85 mg/L; Dissolved Oxygen, 7.35 ± 1.42 mg/L and Biological Oxygen Demand (BOD) 2.41 ± 0.47 mg/L were within stipulated ranged as safe for aquatic organism. Eleven Macrophytes belonging to eight families were fed to the manatee daily. The morphometric measurement showed total length 192 cm, standard length 152 cm, body weight 265 kg, fluke width 36 cm, flipper length 36 cm, head length 34 cm, girth at umbilicus 120 cm, girth at genital pore 82 cm, girth at anus 64 cm. The results indicate that the semi-wild environment provides favourable conditions for the survival of the manatee.

Oil and Gas Pipeline Construction-Induced Forest Fragmentation and Biodiversity Loss in the Niger Delta, Nigeria

The impacts of oil and gas pipeline construction on the forest and biodiversity in parts of the Niger Delta was investigated. This was achieved by studying the construction activities and operational phases of two pipelines with cumulative length of 165 km vis-à-vis the biodiversity of the affected area. The study involved field sampling along the RoWs to inventorize the fauna and flora, visual assessments and interview with locals. It was observed that the pipelines traversed moist lowland/freshwater swamp and mangrove forests, and barrier islands with approximately 4,950,000 m2 (equivalent of 495 hectares) of forest cleared and 9,642,000 trees killed to realize the pipelines. A total of 219 plant species in 66 families and 125 different fauna species from 64 families were recorded in these areas. Three out of the 4 recorded species of Meliaceae were threatened based on IUCN Conservation Status. Also based on IUCN Conservation Status, 20 mammals, including Pan troglodytes, Cercopithecus erythrogaster and Trichechus senegalensis, 7 birds, 2 reptiles and 1 amphibian were within threatened group. The results showed that the study area had witnessed colossal loss of biodiversity due to habitat displacement, forest fragmentation and deforestation, and escalated exploitation of species. The study identified the most affected biodiversity, and proffered measures to mitigate such occurrences.

Conservation Status of Manatee (Trichechus Senegalensis Link 1795) in Lower Sanaga Basin, Cameroon: An Ethnobiological Assessment

An ethnobiological survey of 174 local resource users was conducted in the Lower Sanaga Basin to assess the current conservation status of West African manatee ( Trichechus senegalensis, Link 1795) within lakes, rivers, and coast (including mangroves, estuaries and lagoons). Using a multistage sampling design with semi-structured interviews, the study asked three main questions: (i) are manatees still present in Lower Sanaga Basin? (ii) If present, how are their numbers evolving with time? (iii) What are the main threats facing the manatee? Each of these questions led to the formulation and formal testing of a scientific hypothesis. The study outcome is as follows: (i)60% of respondents sighted manatees at least once a month, regardless of habitat type (rivers, lakes, or coast) and seasons (dry, rainy, or both); (ii) depending on habitat type, 69 to 100% of respondents perceived the trend in manatee numbers as either constant or increasing; the increasing trend was ascribed to low kill incidence (due either to increased awareness or lack of adequate equipment) and to high reproduction rate; and (iii) catches (directed or incidental) and habitat degradation (pollution) ranked in decreasing order as perceived threats to manatees. The catch incidence is threefold larger on lakes than in rivers and more adult manatees are caught than juveniles. Pollution occurs in several places by fishing enterprises, industrial plantations and individuals. The perceived incidence of boat collisions is presently negligible compared to catches and habitat degradation. A twelve-point strategy is set forth for improving manatee conservation in the study area.