The African manatee (Trichechus senegalensis), also called the West African manatee, is a type of manatee that lives in many areas of Western Africa, from Senegal to Angola. It is the only manatee species found in the Old World. This species is one of two living Sirenians that live in the Old World, with the other being the dugong.
Taxonomy
The African manatee was classified as a species in the Trichechus senegalensis taxon in 1795 by naturalist Johann Heinrich Friedrich Link. No subspecies of this taxon have been identified. African manatees live in both coastal areas and separated inland areas. Genetic studies show no major differences between these populations. The African manatee belongs to the genus Trichechus, which includes only two other species: the Amazonian manatee and the West Indian manatee. These animals are also sirenians.
Range and habitat
African manatees live in the most varied types of habitats among all manatee species. They can be found on offshore islands in the Atlantic Ocean, in rivers of the western Sahel region, in equatorial rainforest rivers, and other areas. Coastal manatees often move up rivers during the rainy season and return to the coast during the dry season. The movement and habitats of African manatees have been harmed by the construction of dams for farming and electricity, which have separated manatee groups. For example, the Akosombo Dam in Ghana has divided manatee populations. The Diama Dam in Senegal and the Felou Dam in Mali have permanently cut off manatee groups from the coast.
African manatees are found in many countries in West Africa, including Angola, Benin, Cameroon, Chad, the Republic of the 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. They live in both brackish water and freshwater environments, such as oceans, rivers, lakes, coastal estuaries, reservoirs, lagoons, and bays. African manatees rarely live in water that is colder than 18°C (64°F).
Manatees can be found as far as 75 kilometers (47 miles) from the shore in shallow coastal areas and calm mangrove creeks filled with seagrass. Inland lakes where manatees live include Lake Volta, the Inner Niger River Delta in Mali, Lake Léré, and Lake de Tréné. Some of these lakes act as safe places for manatees during the dry season when river water levels drop. Rivers that support manatees range from north to south, including the Senegal, Saloum, Gambia, Casamance, Cacheu, Mansôa, Geba, Buba, Tombali, Cacine, Kogon, Konkouré, Sierra Leone, Great Scarcies, Little Scarcies, Sherbro, Malem, Waanje, Sewa, Missunado, Cavalla, St. Paul, Morro, St. John, Bandama, Niouniourou, Sassandra, Comoé, Bia, Tano, Volta, Mono, Oueme, Niger, Mekrou, Benue, Cross, Katsena Ala, Bani, Akwayafe, Rio del Rey, Ngosso, Andokat, Mene, Munaya, Wouri, Sanaga, Faro, Chari, Bamaingui, Bahr-Kieta, Logoné, Mitémélé, Gabon, Ogooué, Lovanzi, Kouilou, Congo, Dande, Bengo, and Cuanza. Manatees swim up these rivers until they reach shallow waters or strong waterfalls that block their path.
The areas with the most manatees include Guinea-Bissau, the lagoons of Côte d'Ivoire, the southern parts of the Niger River in Nigeria, the Sanaga River in Cameroon, the coastal lagoons of Gabon, and the lower parts of the Congo River. In a study in Côte d'Ivoire, scientists radio-tagged some manatees to track their movements. The study found that most manatees lived in coastal lagoons, mangroves, and other vegetated areas. They were also found in grassy estuaries of large rivers with mangroves and in protected coastal areas with less than 3 meters (10 feet) of water that contain both mangroves and marine plants.
Diet
Manatees are omnivores and sometimes eat clams, shellfish, and fish found in nets. The amount of non-plant items in their diet depends on where they live. Manatees living near the coast have an average of 50% non-plant material in their diet over their lifetime. The West African manatee is the only sirenian that appears to intentionally eat non-plant material. Most of the African manatee’s diet includes a range of plants that grow above or hang over the water. African manatees in rivers mainly eat plants that grow along the riverbanks. African manatees living in estuaries only eat mangrove trees. Each day, an African manatee consumes about 4% to 9% of its body weight in wet vegetation. Microorganisms in the African manatee’s large intestine, which can be as long as 20 meters (about 66 feet), help it digest the large amount and variety of plants it eats daily.
Description
The African manatee has a body that is widest in the middle, and its tail looks like a paddle. The manatee is gray in color and has small, colorless hairs covering its body. Algae and tiny organisms often grow on its skin, making its body sometimes look brown or green. Baby manatees, called calves, are darker in color when they are very young. African manatees can grow up to 4.5 meters (15 feet) long and weigh about 360 kilograms (790 pounds). They usually move very slowly, traveling about 4.8 to 8.0 kilometers (3 to 5 miles) per hour. However, when they are scared by predators, they can swim faster, reaching speeds of about 32 kilometers (20 miles) per hour. The manatee’s large front flippers are used to paddle through water and bring food to its mouth. It eats plants, which it chews with strong molars—these are the only teeth it has. When a manatee is born, it has two small, baby teeth in each jaw, but these teeth disappear as it grows. If the molars are lost, new molars grow in their place. The manatee’s flippers, which have nails, are also used to touch or graze other manatees. African manatees do not have hind limbs. From the outside, they look similar to American manatees, but they are different from Amazonian manatees, which have white markings on their bellies.
Evolution and legends
The West African manatee is a relative of trichechids that lived in coastal South America during the Pliocene Epoch. Although they usually live in freshwater, scientists believe that ocean currents helped the species reach West Africa during the late Pliocene. The manatee’s appearance is thought to be influenced by these currents and the movement of species across oceans. The African manatee’s ancestors passed on traits that helped them migrate and find food. The African manatee is not limited to one area and does not depend on a single ecosystem for survival. This diversity may help the manatee survive better. They are more varied than other manatees because they can live in salt water, though they still need fresh water to drink.
In West Africa, Maame Water (also spelled Mami Wata) is a goddess in coastal legends. She is seen as a symbol of wealth and beauty and is said to overturn canoes and invite their passengers to her underwater kingdom. Scientists from the Institute of Aquatic Biology at the Centre for Scientific and Industrial Research (CSIR) and Ghana’s Wildlife Department believe Maame Water is inspired by the West African manatee. Dr. Mamaa Entsua-Mensah from CSIR explains that when female manatees surface for air, their appearance resembles that of a goddess. He notes that the shape of their bodies, especially their breasts, can look like those of a woman.
Among the Serer people of Senegal, the Gambia, and Mauritania, the manatee is considered sacred and respected. In Serer creation myths, the manatee is believed to guard the secrets of the future.
Behavior
The African manatee is nocturnal. They usually move quietly, eat, and are active in the late afternoon and during the night. During the day, they rest in shallow water, which is about 1 to 2 meters deep. In countries like Sierra Leone, African manatees move upstream when rivers flood in June and July. This flooding can reduce the amount of food available to them and decrease the salt level in the water. African manatees often live in groups of 1 to 6. They have few natural predators, including sharks and crocodiles. They are also social animals, spending much of their time connecting with others through touch, sounds, and smell. This helps them form strong relationships. When weather changes require them to move, manatees travel in larger groups to find warmer water and more food.
Reproduction
The sex of an African manatee can only be checked by looking closely at the animal’s underside. The only visible difference between males and females is the genital areas. However, males are usually smaller than females. Some female African manatees can have babies as young as 3 years old. They give birth about every 3 to 5 years during their estimated 30-year lifespan. Males take longer to reach maturity, which happens around 9 to 10 years old. They rarely can make a baby at 2 or 3 years old. African manatees can breed anytime during the year. When males and females mate, they do not stay with one partner. Usually, one female mates with several males. When males compete for the chance to mate with a female, they may push and shove each other. Female African manatees give birth to one calf at a time after about 13 months of pregnancy. Calves can swim on their own right after being born. Although scientists do not fully understand how African manatees organize socially, research shows the strongest relationships are between a mother and her calf.
Threats
The African manatee is a species at risk because people hunt it for its meat, oil, bones, and skin, which can be sold for money. These parts are used to make items like walking sticks and toy spinning tops. In some countries, such as Nigeria and Cameroon, African manatees are sold to zoos, aquariums, and online as pets. They are sometimes sent to other countries. Visitors to these areas may see manatee meat for sale in markets, but weak laws and poor enforcement allow poachers to avoid being punished. In countries like Mali and Chad, people use manatee oil to treat health issues such as ear infections, rheumatism, and skin problems.
Other dangers to manatees include human activities that harm their environment. These include building cities and farms, creating more dams, and using more hydroelectric power in rivers of countries like Côte d'Ivoire and Ghana. Dams have caused some manatee populations to become isolated genetically. Scientists do not yet know if this harms the species long-term. Manatees have been killed by turbines and intake valves at dams such as the Kanji Dam on the Niger River and the Akosombo Dam on the Volta River. Heavy boat traffic can lead to manatees colliding with vessels. Natural events, such as droughts and changes in water levels, can also trap manatees in areas where they cannot survive. Some manatees are accidentally killed by fishing nets meant for sharks.
Some manatee behaviors encourage humans to hunt them. When manatees get stuck in fishing nets, they can damage the nets. In countries like Sierra Leone, people believe killing manatees reduces the need to repair expensive nets. Additionally, manatees may destroy rice crops by entering fields during the rainy season.
Many manatees that travel up the Niger River die from starvation. Each year, the river dries up because of high temperatures and little rain. Manatees often move to the river during the rainy season. When the water level drops, they cannot reach other water sources.
Manatees have few natural predators besides humans. Sharks and crocodiles sometimes hunt them, but this is uncommon because these animals live in different habitats. In West Africa, West African crocodiles are the main predators of manatees, aside from humans.
Conservation
From November 2004 to December 2007, the West African Manatee Conservation Project finished Phase I. During this time, people in six African countries (Mauritania, Senegal, The Gambia, Guinea, Guinea-Bissau, and Sierra Leone) gathered new information about the African manatee, such as its population, value to the economy, and where it lives. They did this by conducting surveys in their countries. Other African countries also shared reports that helped increase understanding of the African manatee. Because of this work, people of all ages, including children and scientists, now have better information about how to protect the manatees. Phase I also allowed scientists to closely study the manatee's daily life through fieldwork.
Because Phase I was very successful, Wetlands International will start Phase II. During Phase II, the information collected in Phase I will be shared more widely in the areas where the African manatee lives. Phase II will continue the research from Phase I and work to change laws and improve education about manatees.
The African manatee is listed on Appendix I of the Convention on International Trade in Endangered Species (CITES), which means that trading the manatee across international borders is strictly controlled. Laws exist in every country where the manatee lives to protect it, but these laws are not followed well. Because of poor enforcement and little education, the number of African manatees is slowly decreasing.