Amazonian manatee (Trichechus inunguis)

Also known as: peixe-boi (Brazil), sea cow, South American manatee
  
French: Lamantin D'Amérique Du Sud, Lamantin De L'Amazone
Spanish: Lamantino Amazónico, Manatí Amazónico, Vaca Marina
KingdomAnimalia
PhylumChordata
ClassMammalia
OrderSirenia
FamilyTrichechidae
GenusTrichechus (1)
SizeLength: up to 2.8 meters (2)
Weight350 – 500 kg (3)

The Amazonian manatee is classified as Vulnerable (VU) on the IUCN Red List (1), listed on Appendix I of CITES (4), and listed as Endangered by the US Endangered Species Act. (5). The Amazonian manatee also has a Global Heritage Status Rank of G2 (5).

The Amazonian manatee is a most bizarre-looking aquatic mammal, and was first described as a curious combination of a hippopotamus and a seal (6). Its body is large, dark grey to black and smooth-skinned, and its forelimbs are modified into flippers like a seal’s (7). It has no hind limbs, and the rear of the body forms a flat, rounded horizontal paddle (8). The head is rounded, with nostrils on the upper surface of the snout (9). The Amazonian manatee is smaller and more slender than the other two manatee species (West Indian manatees Trichechus manatus and West African manatees T. senegalensis) (8). It can also be identified by the lack of nails on its flippers, a characteristic referred to in its scientific name, T. inunguis, which literally means ‘no nails’ (10). A unique feature (amongst mammals) of the manatee is the constant replacement of molar teeth; new teeth enter at the back of the jaw and replace old and worn teeth at the front (11). Recent evidence suggests that manatees may possess a unique 6th sense that enables them to detect pressure changes through sensory hairs (12).

The Amazonian manatee is found in the Amazon River Basin from the river mouth to the upper reaches of calm water tributaries of Brazil, Colombia, Ecuador, Guyana, and Peru (2) (7).

The Amazonian manatee inhabits areas of the Amazon River where there are freshwater lagoons, oxbow lakes and blackwater lakes. It requires waterways with deep connections to large rivers and abundant aquatic vegetation (8).

Amazonian manatees are aquatic mammals and live almost entirely underwater. Indeed the three manatee species and the closely related dugong are unique in that they are the only plant-eating marine mammals (8). They feed entirely on aquatic vegetation near lake edges, such as emergent grasses, water lettuce and floating vegetation. Shy and secretive, only their nostrils protrude from the surface of the water to breathe as they search for lush vegetation (8). Despite being slow grazers they are able to consume up to eight percent of their body weight in one day (2) (8). Most feeding occurs during the wet season, when they graze upon new plant growth in seasonally flooded water. During the dry season, individuals return to the main water courses, or to deep flooded backwaters where herds congregate (8). Here they may not eat for weeks or months due to the lack of food. However, manatees have large fat reserves and slow metabolic rates; at one third of the usual rate for a mammal of its size. This enables them to survive until the water levels rise again and food becomes more abundant (2) (8).

These mammals are active by day and night. They are found individually or in small groups of between four and eight animals (8). Mothers nurse their calves from a teat behind the flipper, and it is the mothers and calves that form the closest bonds (8) (9). A single calf is born after a gestation period of approximately 13 months. It is dependant on its mother for a considerable time, so interbirth intervals may be as long as three and a half years or more. Individuals mature at five or six years of age and members maintain group contact by underwater vocalisations (9). The lifespan of this animal is unknown, but individuals have lived past twelve and a half years in captivity (8).

Once known to occur in large herds and have healthy populations (2), the Amazonian manatee has suffered from extensive hunting by subsistence and commercial hunters. It has been sought for meat, oil and fat, and at one time for its hide, which was in demand for use as water hoses and machine belts (8). Threats now include hunting and accidental drowning in commercial fishing nets. The deforestation of large areas of the forests surrounding this manatee’s river habitats has also caused soil erosion, degradation of food supplies and the reduction of vegetation in the waterways (8).

International trade of the Amazonian manatee is prohibited due to its listing on Appendix I of CITES (4). This species has suffered huge losses but is locally abundant in the more remote regions of the Amazonian River Basin. However, it is very difficult to control hunting in these economically depressed areas and they are still killed for meat (3). While numerous federal, state, and local conservation measures are in place to protect the Florida manatee (T. manatus latirostris), South America has limited resources for funding comprehensive conservation projects. Several effective programs in Brazil include surveys by Projeto Peixe-Boi/Center for Aquatic Mammals (15), sustainable use research by Mamirauá Project (16), and education/outreach efforts by The Friends of the Manatee Association (17). The Harbour Branch Division of Marine Mammal Research and Conservation conducts manatee conservation outreach programs in Brazil and plays an important role in rehabilitating injured, sick or orphaned individuals (13). It is hoped that these measures combined with stronger hunting laws will allow the ancient and wonderful Amazonian manatee to recover (13) (14).

To find out more about the Amazonian manatee, visit:

Authenticated (16/02/05) by Jim Reid, US Geological Survey Sirenia Project.
http://sofia.usgs.gov/people/reid.html

  1. IUCN Red List (August, 2009)
    http://www.redlist.org
  2. Animal Diversity (November, 2003)
    http://animaldiversity.ummz.umich.edu/accounts/trichechus/t._inunguis$narrative.html
  3. Emmons, L. (1990) Neotropical Rainforest Mammals. University of Chicago Press, USA.
  4. CITES (November, 2003)
    http://www.cites.org
  5. US Fish and Wildlife Service, Endangered Species Act (November, 2003)
    http://endangered.fws.gov/esa.html
  6. Wood, J.G. (1860) The Illustrated Natural History - Mammalia. The Youth’s Companion. Boston, MA.
  7. Reid, J. (2005) Pers. comm.
  8. Animal Info (November, 2003)
    http://www.animalinfo.org/species/tricinun.htm
  9. Eisenberg, J.F. (1989) Mammals of the Neotropics. University of Chicago Press, USA.
  10. Sirenian International (November, 2003)
    http://www.sirenian.org/index.html
  11. Macdonald, D. (2001) The New Encyclopedia of Mammals. Oxford University Press, Oxford.
  12. UNEP – WCMC (November, 2003)
    http://www.unep-wcmc.org/
  13. Projeto Peixe-Boi/IBAMA-Center for Aquatic Mammals (February, 2005)
    http://www.projetopeixe-boi.com.br/
  14. Mamirauá Project (February, 2005)
    http://www.cnpq.br/mamiraua/mamiraua2.htm
  15. The Friends of the Manatee Association (February, 2005)
    http://www.amigosdopeixe-boi.org.br/
  16. Harbour Branch Division of Marine Mammal Research and Conservation (November, 2003)
    http://www.hboi.edu/marinemam/bossart.html
  17. Save the Manatee Club (February, 2005)
    http://www.savethemanatee.org/