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Looking like a cross between a cow and giant frog, it's hard to believe that the manatee is the origin of the mythical mermaid (a beautiful woman with the tail of a fish rather than legs). Early descriptions compared it to a combined hippopotamus and seal. The Amazonian manatee is the smallest of the sirenians, the family of mammals to which they belong. Even so, tipping the scales at up to 1100 pounds (500 kg), they are by far the biggest Amazonian mammals. Sirenians are unique as the only living fully aquatic mammals that are exclusively herbivorous.

The Amazonian manatee (Trichechus inunguis) is similar in appearance to its better known cousin, the West Indian manatee (T. manatus), which is somewhat larger. The manatee has a cylindrical cigar-shaped body ending in a flat paddle-like tail. Its body is hairless, a uniform gray except for an irregularly-shaped white patch on the underside. The front flippers are small and rounded, offering some manouvering capability but otherwise serving little function. The manatee's small head has tiny eyes (hence poor eyesight) and lacks an external ear, while the mouth and lips are highly modified, covered with bristles, giving the appearance of a walrus (without tusks).

The Amazonian manatee is found in remote swampy lakes and slow-moving rivers where aquatic food plants are abundant. It tends to prefer black water lakes that are fairly acidic. Highest populations are in areas far from human habitations because hunting pressure has eliminated the manatee from many parts of its former range. Populations persist in northern Peru and Ecuador along the main stream of the Amazon to the mouth, with an isolated population in southern Guyana. Local populations disperse according to the season. When water levels are high during the rainy season, manatees move to heavily vegetated backwaters and when flood waters recede, they move back into larger rivers. Manatees live entirely underwater, never breaking the surface except for their nostrils when they come up to breathe. They surface every four minutes or so (14 minutes is the record time spent underwater), taking two to four breaths in rapid succession.

Manatees are exclusively vegetarian, consuming up to 100 pounds, or about 50 large lettuces, of aquatic vegetation per day. Their preferred diet comprises floating grasses , water hyacinth and water lettuce. According to Colares & Colares (2002), manatees are more selective during high water, when eight species were identified as food plants. During low water, the animals foraged on a greater diversity of plants, comprising 21 species in all.

An average amount of food is about 20 to 35 pounds daily. Even so, the quantity of plant matter is so great that manatees play a role in keeping waterways open. The diet of the Amazonian manatee is partially dependent on their seasonal dispersal (see Habitat and Distribution above). For the manatee mealtime is "feast or famine." During the flood season, they retreat to backwaters in areas of dense aquatic vegetation. As the flood waters recede, much of this vegetation is washed into main channels, while lakes and swamps may become too shallow so the manatees must move to deeper waters where their food is typically less abundant. Scientist have found that the manatee has a very slow metabolism, which enables it to go for long periods during the dry season with little or no food. Manatees' molar (chewing) teeth are unique among mammals, being replaced throughout life as they are worn out, which is quite quickly considering the coarse plants upon which they feed. New teeth erupt at the back of the jaw then migrate forward to replace old and worn teeth at the front. The Amazon manatee may feed alone or in groups up to eight individuals.

Most detailed knowledge of breeding in manatees is known from studies of the West Indian manatee. Amazonian manatee breeding is tied to seasonal food availability. To coincide with the cycle of food availability, calves are usually born just as the rivers begin to flood at the start of the rainy season. Because of geographic variation, breeding season may differ from one location to another. According to, breeding may occur year-round while in one part of the Ecuadorian Amazon, birthing takes place in January, but in another part it peaks in June. In central Amazonia, however, the peak period is from February to May, as river levels are rising. Nearly all births take place between December to July. Gestation takes about a year whereupon a single calf is born; the female carries very young calves on her back or held to her side. Calves suckle from a teat behind the mother's flipper. After birth the calf remains with the mother for some time, so two or three years may pass between birthing. Individuals mature around five or six years. The lifespan in the wild is not known, although some authorities cite a figure of 60 years. Captive animals have lived as long as twelve years.

The Amazonian manatee is regrettably among the most endangered mammals in South America. Although protected by CITES and the Endangered Species Act (listed as Endangered) its numbers have been drastically reduced by hunting, habitat degradation, snarling in fishing nets and other environmental impacts.
Hunting is still significant in remote areas, and like whalers of old, remains a tradition that's hard for local people to give up. Here's an account from memory as told to the author in a poignant and heartfelt description by Sñr. Daniel Rios, naturalist guide aboard the tourist riverboat, El Arca, for many years until the mid-1990's.
See a painting by Daniel Rios)

The hunter will not usually go out to specifically look for manatee, the animals are too rare to be reliable prey. Rather, the hunter will notice the manatee's dung, which floats in copious quantities looking like horse droppings. He follows the trail relentlessly. Upon seeing the nostrils break the surface, the hunter hurls his harpoon at the unsuspecting creature. If the aim is true, the hunter is then taken on a ride (akin to the old whalers' "Nantucket sleigh ride") as the manatee takes flight. He and his boat may be towed for hours as the huge creature takes a long time to tire. But eventually it does. When it comes to the surface, exhausted, breathing heavily, the hunter takes a pair of wooden plugs and stuffs them into the nostrils. It's not long before the manatee dies of suffocation. Placed in reused cooking oil cans, the meat is stored in its own oil, so rich that it does not go rancid for months. The meat is delicious, very rich, and has high nutritional value, and is much favored above other kinds, so fetches a good price at market. It is not a prize that the hunter can overlook.

To our eyes, the hunting technique seems rather barbaric, but the prospect of a manatee cannot be turned down by a poor hunter who will feed his family for weeks and be able to sell the meat for a premium at local markets. Of course, like overfishing, the vicious cycle is practically impossible to break—as the manatee gets rarer, people pay higher and higher prices for its meat, ever increasing the incentive for hunters.

But there is hope for the manatee, on account of its prodigous plant-eating capacity, and hence importance in the aquatic ecosystem. Brazilian authorities found that acidity of decaying aquatic vegetation in a dammed lake eroded the electricity-generating turbines, quickly rendering the machines useless. Following introduction of manatees, the vegetation was quickly brought under control, ensuring continued operation of the turbines. In Guyana, according to Wikipedia, three manatees at the main water treatment plant has keep storage canals clear of weeds.


Amazonian Manatee
Arkive: Amazonian manatee (Trichechus inunguis) Amazonian Manatee
Animal Info: Amazonian Manatee
Animal Diversity Web: Trichechus inunguis (Amazonian manatee)
Sirenian International: Amazonian Manatees (Trichechus inunguis
FAO Species Fact Sheet: Trichechus inunguis
ITIS report: Trichechus
IUCN Red List data: Trichechus inunguis
Website of Everything: Pictures and facts about the Amazonian manatee
Mongabay: Educational resources on Amazonian Manatee
Experientia: Sleep in an Amazonian manatee, Trichechus inunguis.
Biol Chem Hoppe Seyler.: The primary structure of the hemoglobin of the Brazilian manatee (Trichechus inunguis, Sirenia)
Colares & Colares (2002) Food Plants Eaten by Amazonian Manatees (Trichechus inunguis, Mammalia : Sirenia) Brazilian Archives of Biology and Technology: 45(1) DOI:10.1590S1516-89132002000100011
Cantanhede, A. M. et al. (2005) Phylogeography and population genetics of the endangered Amazonian manatee, Trichechus inunguis Molecular Ecology 14: 401 DOI:10.1111/j.1365-294X.2004.02413.x

Manatees (Sirenians) generally
Encarta: Manatee
Wikipedia: Manatee
All About Manatees
Smithsonian Institution: Selected References on the Sirenia
Manatee Brain Project
Save the Manatee Club
Sirenian International
Sound in the Sea: Manatee (Trichechus spp.)
Vianna, J. A. et al. (2006) Phylogeography, phylogeny and hybridization in trichechid sirenians: implications for manatee conservation. Molecular Ecology 15: 433 DOI:10.1111/j.1365-294X.2005.02771.x
Santa Cruz Public Libraries: Fossil Sea Cow

Mainly photos
Ardea: Manatee
Skulls Unlimited: Amazon Manatee Skull Sirenen
Photo Researchers: Manatee
Seapics: Manatee

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