The Amazonian manatee (Trichechus inunguis), which is sometimes called cowfish in Brazil, is a type of manatee found in the Amazon Basin of Brazil, Peru, Colombia, and Ecuador. It has thin, wrinkled skin that is brownish or gray in color, with fine hairs spread across its body and a white patch on its chest. It is the smallest of the three manatee species that still live today.
Taxonomy
The specific name, inunguis, is Latin for "nailless." The genus name, Trichechus, comes from the Latin word meaning "hair," which refers to the whiskers around the manatee's mouth.
Physical characteristics
The Amazonian manatee is the smallest manatee and can be identified by its smooth, rubbery skin and the absence of small, leftover nails on its flippers. Captive male manatees weigh between 7.5 and 346 kilograms (about 17 to 763 pounds) and measure 76 to 225 centimeters (about 2 feet 5.9 inches to 7 feet 4.6 inches) in length. Captive females weigh between 8.1 and 379 kilograms (about 18 to 836 pounds) and measure 71 to 266 centimeters (about 2 feet 4 inches to 8 feet 8.7 inches) in length. Free-ranging manatees weigh between 120 and 270 kilograms (about 264.6 to 595.2 pounds) and measure 162 to 230 centimeters (about 5 feet 3.8 inches to 7 feet 6.6 inches) in length. The heaviest recorded Amazonian manatee weighed 379 kilograms (about 836 pounds). Newborn manatees weigh between 10 and 15 kilograms (about 22 to 33 pounds) and measure 85 to 105 centimeters (about 33 to 41 inches) in length. These manatees grow in length by about 1.6 to 2.0 millimeters each day, measured along the curve of their bodies. This means their actual lengths may vary. As calves, they gain about 1 kilogram in weight each week.
Amazonian manatees are large, rounded mammals with flippers for their front limbs, no hind limbs, and a flat, rounded tail. Their flexible flippers help them move along the seafloor, scratch, touch, and even hold onto other manatees. They also use their flippers to move food into their mouths and clean them. Their upper lip is large, bristly, and deeply split, allowing each side to move independently while eating. Most manatees have a gray color with a white or bright pink patch on their chest.
Like all manatees in the Trichechidae family, Amazonian manatees have teeth that are continuously replaced throughout their lives. Their teeth move from the back of the jaw to the front, a unique feature among mammals. Only elephants, which are closely related to manatees, have a similar trait, but elephants have fewer replacement teeth. As manatee teeth move forward, their roots are broken down, and their thin enamel wears away until the tooth is lost. These teeth, called cheek teeth, are not divided into molars or premolars, and manatees lack incisors or canines. Their teeth move at a rate of about 1 to 2 millimeters per month, depending on wear and eating habits.
The Amazonian manatee does not have nails on its flippers, which sets it apart from other manatee species. It also has a small angle (30.4°) between its snout and the back of its jaw, which helps scientists determine where it feeds in the water. A small angle means the snout is nearly straight relative to the jaw. Other manatees, like Dugongs, have a much larger angle (about 70°), which helps them feed on the seafloor. Only the West African manatee (T. senegalensis) has a smaller angle (about 25.8°). A small angle allows Amazonian manatees to feed more efficiently at the water’s surface, where much of their food is found.
Behavior and biology
The Amazonian manatee is the only sirenian that lives only in freshwater environments. This species uses changes in blood flow to regulate body temperature. Special muscles control blood flow away from areas in contact with water, and thick fat under the skin helps reduce heat loss.
Manatees have nostrils, not blowholes like whales, which close underwater to keep water out and open above water to breathe. Although manatees can stay underwater for long periods, they usually surface for air every five minutes. The longest recorded time an Amazonian manatee stayed underwater in captivity was 14 minutes.
Manatees move seasonally based on water levels in the Amazon Basin. During the flood season, they live in flooded forests and meadows where food is plentiful. The Amazonian manatee has the smallest snout angle (25° to 41°) among sirenians, which helps them feed closer to the water surface. They are active both during the day and night and spend most of their lives underwater. Only their nostrils remain above water as they search river and lake bottoms for plants.
The Amazonian and West Indian manatees are the only manatees known to make sounds. These sounds occur when they are alone or with others, especially between mothers and their young.
Amazonian manatees eat a variety of underwater plants, including water lettuce, grasses, bladderworts, hornworts, water lilies, and water hyacinths. They also eat fallen palm fruits. Their digestion process after eating is similar to a horse’s. Manatees consume about 8% of their body weight in food each day.
During the July–August dry season, when water levels drop, some manatees move to deep parts of large lakes. They may not eat for months, relying on stored fat and a slower metabolism—only 36% of the usual rate in mammals—to survive up to seven months with little food.
The Amazonian manatee breeds seasonally, with a pregnancy lasting 12–14 months. Most births occur between December and July, with about 63% happening between February and May, when river levels rise. Calves begin eating while staying with their mothers for 12–18 months.
Wild Amazonian manatees live about 30 years. The longest recorded lifespan in captivity is 17 years.
Population and distribution
As of 1977, scientists estimated that there were about 10,000 Amazonian manatees. Today, the exact number of manatees is unknown, but their population appears to be getting smaller. These manatees live mainly in the Amazon River Basin in northern South America, from the Marajó Islands in Brazil to countries like Colombia, Peru, and Ecuador. Occasionally, they are found near the coasts of Brazil, where they may share areas with West Indian manatees.
Amazonian manatees are found throughout most of the Amazon River system, starting in the river’s headwaters in Colombia, Ecuador, and Peru and ending near the mouth of the river near Marajó Island in Brazil. This area covers about seven million square kilometers. However, manatees are not spread out evenly; they are more common in areas with rich nutrients and flooded forests, which cover about 300,000 square kilometers. They also live in lowland tropical regions below 300 meters above sea level, where there are many aquatic and semi-aquatic plants. These manatees prefer calm, shallow waters far from human settlements.
Amazonian manatees spend their entire lives in water and never leave the water. They are the only manatee species that lives only in freshwater environments. They often stay in backwater lakes, oxbows (curved river channels), and lagoons that are connected to large rivers and have plenty of aquatic plants. Manatees are usually alone but may sometimes form small groups of up to eight individuals. They move seasonally, traveling from flooded areas during the wet season to deeper water during the dry season.
Natural predators of Amazonian manatees include jaguars, sharks, and several types of caimans, such as the spectacled caiman, black caiman, Cuvier’s dwarf caiman, and smooth-fronted caiman.
Illegal hunting
The main danger to the Amazonian manatee is illegal hunting. People hunt them for food and local use, not for selling in stores. This hunting has caused the manatee population to drop greatly, leaving very few remaining. Between 1935 and 1954, more than 140,000 manatees are believed to have been killed. Even though laws exist to stop hunting, it still happens, including in areas meant to protect wildlife. Hunters often use traditional harpoons, but in Ecuador, manatees are also caught in traps used for fishing Arapaima fish.
Manatees are hunted mainly for their meat, which is valuable. Their fat and skin are also used for cooking and in medicines. The meat is sold to nearby people or at local markets. In some places, it is illegally sold as sausage or mixira in public markets in Brazil and Ecuador. Mixira is a type of preserved meat stored in its own fat and is expensive, which encourages hunters to continue killing manatees.
Between 2011 and 2015, 195 manatees were killed for meat in one region of Brazil. In another area, 460 manatees were killed in a protected area from 2004 to 2014.
Conservation
The IUCN Red List classifies the Amazonian manatee as vulnerable. Population decreases are mainly caused by hunting, calf deaths, climate change, and loss of habitat. However, because manatees live in murky water, it is hard to determine their exact numbers.
Only Colombia has national management plans for the Amazonian manatee. In 2008, the INPA cared for 34 manatees in captivity, and the CPPMA cared for 31 manatees. Peruvian law has protected the manatee since 1973 through Supreme Decree 934-73-AG, which bans hunting and commercial use of the manatee.
Hunting remains the biggest threat and continues in many areas, even inside protected reserves. In 1986, scientists estimated that hunting levels in Ecuador were so high that the manatee might disappear from the country within 10 to 15 years. Although hunting still happens, oil spills now pose a growing risk to manatees in Ecuador. Oil exploration also increases boat traffic on rivers.
In Peru, manatees have declined mainly because people hunt them for meat, blubber, skin, and other materials. Hunters use harpoons, gillnets, and traps. Much of this hunting occurs in lakes and streams near the Pacaya-Samiria National Reserve in northeastern Peru. Manatees move slowly and are gentle, often seen feeding at the water’s surface. They also face dangers like pollution, drowning in fishing nets, and loss of plants due to deforestation. Mercury released from mining harms the entire aquatic ecosystem of the Amazon Basin.