West Indian Manatee

West Indian Manatee[1]
Conservation status

Vulnerable (IUCN 3.1)[2]
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Sirenia
Family: Trichechidae
Genus: Trichechus
Species: T. manatus
Binomial name
Trichechus manatus
Linnaeus, 1758

The West Indian Manatee (Trichechus manatus) is a manatee, and the largest surviving member of the aquatic mammal order Sirenia (which also includes the Dugong and the extinct Steller's Sea Cow). The West Indian Manatee, Trichechus manatus, is a species distinct from the Amazonian Manatee, T. inunguis, and the West African Manatee, T. senegalensis. Based on genetic and morphological studies, the West Indian Manatee is divided into two sub-species, the Florida Manatee (T. m. latirostris) and the Antillean Manatee or Caribbean Manatee (T. m. manatus).[3][4] However, recent genetic (mtDNA) research suggests that the West Indian manatee actually falls out into 3 groups, which are more or less geographically distributed as: (1) Florida and the Greater Antilles; (2) Central and Northern South America; and (3) Northeastern South America.[5][6]

Contents

Physical description

Like other manatees, the West Indian Manatee has adapted fully to an aquatic life style, having no hind limbs. Pelage cover is sparsely distributed across the body, which may play a role in reducing the build-up of algae on the skin. The average West Indian Manatee is approximately 3 meters long, and weighs between 400 and 600 kg, with females generally larger than males. The largest individuals can weigh up to 1,500 kg (3,300 lb) and measure up to 4.6 m (15 ft).[7] The Manatee's colour is gray or brown.

Habitat and geographic range

As its name implies, the West Indian Manatee lives in the West Indies, or Caribbean, generally in shallow coastal areas. However, it is known to withstand large changes in water salinity, and so have also been found in shallow rivers and estuaries. It is limited to the tropics and subtropics due to an extremely low metabolic rate and lack of a thick layer of insulating body fat. During summer, these large mammals have even been found as far north as New York City, New York.[8]

The Florida manatee, (Trichechus manatus latirostris) a subspecies of the West Indian manatee, is the largest of all living sirenians. Florida manatees inhabit the most northern limit of sirenian habitat. Over three decades of research by universities, governmental agencies, and NGOs, have contributed to our understanding of Florida manatee ecology and behavior, which is more than we know about any other species. They are found in fresh water rivers, in estuaries, and in the coastal waters of the Gulf of Mexico and the Atlantic Ocean. Females usually have their first calf when they are about 4 years old. Normally they only have one calf every 2–5 years, but there are rare occurrences of twins. The family unit consists of mother and calf, which remain together for up to 2 years. Males aggregate in mating herds around a female when she is ready to conceive, but contribute no parental care to the calf. Florida manatees may live to be greater than 60 years old in the wild. The biggest single threat to Florida manatees is death from collisions with recreational watercraft.

The other subspecies of the West Indian manatee is sometimes referred to as a Caribbean manatee (Trichechus manatus manatus). Antillean manatees are sparsely distributed throughout the Caribbean and the Northwestern Atlantic Ocean, from Mexico, east to the Greater Antilles, and south to Brazil. They are found in French Guiana, Suriname, Guyana, Trinidad (however there has been a lack of recent sightings), Venezuela, Colombia, Panama, Costa Rica, Nicaragua, Honduras, Guatemala, Belize, Mexico, Cuba, Haiti, Dominican Republic, Jamaica, and Puerto Rico. Historically Antillean manatees were hunted by local natives and sold to European explorers for food. Today they are threatened by loss of habitat, poaching, entanglement with fishing gear, and increased boating activity. Several of Sirenian International's scientists study Antillean manatees in Belize, which may be the last stronghold for the subspecies. Funds for research, education, and conservation projects are desperately needed in other Central American nations.

Behavior and food

West Indian Manatee at the Columbus Zoo.

The West Indian Manatee is surprisingly agile in water, and individuals have been seen doing rolls, somersaults, and even swimming upside-down. Manatees are not territorial and do not have complex predator avoidance behavior, as they have evolved in areas without natural predators.

The West Indian Manatee is an opportunistic feeder, with large adults feasting on nearly 9 to 30 kg (20 to 66 lb) of sea grasses and plant leaves daily. Because manatees feed on abrasive plants, their molars are often worn down and are continually replaced throughout life.

Reproduction

Although female West Indian Manatees are mostly solitary creatures, they form mating herds while in estrus. Most females breed successfully between ages of seven and nine, however, females are capable of reproduction as early as four years of age. Gestation period (pregnancies) lasts from twelve to fourteen months. Normally, one calf is born, although on rare occasions two have been recorded. The young are born with molars and premolars, allowing them to consume sea grass within the first three weeks of birth. On average, manatees that survive to adulthood will have between 5 and 7 offspring between the ages of 20 to 26.

Manatee interaction with humans

The West Indian Manatee has been hunted for hundreds of years for meat and hide, and continues to be hunted to this day in Central and South America. Illegal poaching, as well as collisions with speeding motorboats, are a constant source of manatee fatalities.

Due to their low reproductive rates, a decline in manatee population may be hard to overcome. They enjoy protection from the U.S. Endangered Species Act of 1973, and the U.S. Marine Mammal Protection Act of 1972. However, in April 2007, the U.S. Fish and Wildlife Service announced that the West Indian manatee population of Florida had rebounded. It advised that the species be reclassified as "threatened" rather than "endangered". A computer model produced for the federal study showed a 50 percent chance that the current statewide manatee population of about 3,300 could dwindle over the next 50 years to just 500 on either coast.[9]

The Florida manatee subspecies (Trichechus manatus latirostris) was listed in October 2007 as Endangered by the IUCN on the basis of a population size of less than 2,500 mature individuals and a population that is estimated to be in decline by at least 20% over the next two generations (estimated at ~40 years) due to anticipated future changes in warm-water habitat and threats from increasing watercraft traffic over the next several decades.[10]

References

  1. ↑ Shoshani, Jeheskel (16 November 2005). Wilson, Don E., and Reeder, DeeAnn M., eds. ed. Mammal Species of the World (3rd ed.). Baltimore: Johns Hopkins University Press, 2 vols. (2142 pp.). pp. 93. ISBN 978-0-8018-8221-0. OCLC 62265494. http://www.bucknell.edu/msw3. 
  2. ↑ Deutsch, C.J., Self-Sullivan, C. & Mignucci-Giannoni, A. (2008) Trichechus manatus In: IUCN 2009. IUCN Red List of Threatened Species. Version 2009.2. www.iucnredlist.org Retrieved on 2010-01-27.
  3. ↑ Domning and Hayek; Hayek, Lee-Ann C. (1986). "Interspecific and intraspecific morphological variation in manatees (Sirenia: Trichechus)". Marine Mammal Science 2 (2): 87–144. doi:10.1111/j.1748-7692.1986.tb00034.x. 
  4. ↑ Hatt (1934). "The American Museum Congo Expedition manatee and other recent manatees". Bulletin of the American Museum of Natural History 66: 533–566. 
  5. ↑ Garcia-Rodriguez, B. W. Bowen, D. Domning, A. A. Mignucci-Giannoni, M. Marmontel, R. A. Montoya-Ospina, B. Moreales-Vela, M. Rudin, R. K. Bonde, and P. M. McGuire (1998). "Phylogeography of the West Indian manatee (Trichechusmanatus): How many populations and how many taxa?". Molecular Ecology 7 (9): 1137–1149. doi:10.1046/j.1365-294x.1998.00430.x. PMID 9734072. 
  6. ↑ Vianna et al.; Bonde, RK; Caballero, S; Giraldo, JP; Lima, RP; Clark, A; Marmontel, M; Morales-Vela, B et al. (2006). "Phylogeography, phylogeny and hybridization in trichechid sirenians: implications for manatee conservation". Molecular Ecology 15 (2): 433–47. doi:10.1111/j.1365-294X.2005.02771.x. PMID 16448411. 
  7. ↑ Wood, The Guinness Book of Animal Facts and Feats. Sterling Pub Co Inc (1983), ISBN 978-0851122359
  8. ↑ http://www.msnbc.msn.com/id/33341471/ns/local_news-new_york_ny/?GT1=43001
  9. ↑ "Manatees May Lose Status". St. Petersburg Times. 2007-04-10. http://pqasb.pqarchiver.com/sptimes/access/1252260721.html?dids=1252260721:1252260721&FMT=FT&FMTS=ABS:FT&date=Apr+10%2C+2007&author=CRAIG+PITTMAN&pub=St.+Petersburg+Times&edition=&startpage=1.B&desc=MANATEES+MAY+LOSE+STATUS. Retrieved 2007-05-10 
  10. ↑ Deutsch, C.J., Self-Sullivan, C. & Mignucci-Giannoni, A. (2007). Trichechus manatus ssp. latirostris. 2007 IUCN Red List of Threatened Species. IUCN 2007. Retrieved on 2007-12-03.

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