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Order: Sirenia
Family: Trichechidae
The sirenians (manatees and dugongs) are more closely related to elephants than to marine mammals such as whales and dolphins. They belong to an ancient radiation of African mammals known as the Afrotheria. This superorder includes seven groups of animals thought to have shared a common ancestor around 100 million years ago. These animals have little superficial resemblance to each other. Together with the sirenians and elephants, this group also includes the aardvark, hyraxes, sengis (or elephant-shrews), golden moles and tenrecs.
Sirenians are conventionally divided into four families: two, the Prorastomidae and the Protosirenidae, are extinct and known only from the Eocene, while the Dugongidae (dugongs, including Steller’s sea cow) and Trichechidae (manatees) survive today.
The fossil record of the Sirenia extends over 50 million years. The sirenians are thought to have branched off from the Proboscidea (elephants) during the Palaeocene, and quickly dispersed to the New World. The earliest known representative of the group was a pig-sized prorastomid from Jamaica from the early Eocene. This four-legged animal could walk on land, but probably spent much of its time in water. It had an extremely dense skeleton, which acted like ballast to keep the animal submerged in shallow waters. By the middle Eocene, protosirenid sea cows were abundant in North America, Europe and Asia. While the early sirenians had narrow snouts that suggested selective browsing, the muzzles had by this time broadened and became more downturned to ‘mow’ the carpets of seagrass on the ocean floor. The Dugongidae first appeared in the mid-late Eocene of the Mediterranean region. It was among these forms that the loss of the functional hind limbs took place. The manatees (Trichechidae) are the dugong’s closest living relatives. They are thought to have diverged from the Dugongidae at some time between the late Eocene and mid Oligocene.
There are three species of manatee alive today: the Amazonian manatee (Trichechus inunguis), the American or West Indian manatee (T. manatus) and the African manatee (T. senegalensis).
The West Indian Manatee is known to consist of two subspecies, Trichechus manatus latirostris found in Florida and Trichechus manatus manatus which is known as the Antillean manatee.
Sirenians are conventionally divided into four families: two, the Prorastomidae and the Protosirenidae, are extinct and known only from the Eocene, while the Dugongidae (dugongs, including Steller’s sea cow) and Trichechidae (manatees) survive today.
The fossil record of the Sirenia extends over 50 million years. The sirenians are thought to have branched off from the Proboscidea (elephants) during the Palaeocene, and quickly dispersed to the New World. The earliest known representative of the group was a pig-sized prorastomid from Jamaica from the early Eocene. This four-legged animal could walk on land, but probably spent much of its time in water. It had an extremely dense skeleton, which acted like ballast to keep the animal submerged in shallow waters. By the middle Eocene, protosirenid sea cows were abundant in North America, Europe and Asia. While the early sirenians had narrow snouts that suggested selective browsing, the muzzles had by this time broadened and became more downturned to ‘mow’ the carpets of seagrass on the ocean floor. The Dugongidae first appeared in the mid-late Eocene of the Mediterranean region. It was among these forms that the loss of the functional hind limbs took place. The manatees (Trichechidae) are the dugong’s closest living relatives. They are thought to have diverged from the Dugongidae at some time between the late Eocene and mid Oligocene.
There are three species of manatee alive today: the Amazonian manatee (Trichechus inunguis), the American or West Indian manatee (T. manatus) and the African manatee (T. senegalensis).
The West Indian Manatee is known to consist of two subspecies, Trichechus manatus latirostris found in Florida and Trichechus manatus manatus which is known as the Antillean manatee.
Size:
Head and body length: 3-4 m
Weight: Average 500 kg
Adult manatees are grey-brown. Newborns are darker in colour initially but their skin quickly fades to the same colour as the adults. The body is shaped similarly to a seal's and is covered in colourless hair. There are stiff bristles around the mouth. A large paddle shaped tail is used to propel the animal forward, and as a ruder to alter direction. There is a small flipper on either side of the body upon which nails grow on the dorsal side.
The two sub species of West Indian manatee share similar ecological characteristics. When a female manatee is ready to breed males will compete with each other to mate with her and will follow the female in large groups. However the female shows little interest in the males and is often seen trying to escape from their attention. A female is usually pregnant for 12-13 months before giving birth to one calf, or sometimes twins, that can be between 1.2 -1.3 m long. In Florida calves are normally born in the spring and summer but further south in warmer water breeding can occur year round. Calves quickly learn to swim and will remain with their mothers for between 1-2 years. Males reach sexual maturity at about 3-4 years of age but females mature at about 5 years of age. In the wild a female has been known to live till 59 years of age but this is very usual.
Manatees require fresh water for drinking and so will be found in areas such as creeks where fresh water is available. Sea grass is their primary food source and adults may spend hours grazing at a time. In between feeding the manatee will rest suspended at the surface or on the bottom of the water that it is in. Due to a low metabolic rate, manatees find it difficult to thermoregulate and as a consequence are susceptible to mortality in cold temperatures. To overcome this, West Indian manatees will aggregate in large groups in areas of warm water during periods of cold weather.
Florida manatees undertake extensive seasonal migrations with distribution determined by water temperature. When ambient water temperatures drop below 20°C (68°F) in autumn and winter, manatees will aggregate at natural and artificial warm-water refuges or move to southern Florida with most manatees returning to the same warm-water refuges each year. Manatees can be found in very shallow water, as shallow as 0.4 m with their backs out of the water but are usually found in deeper water and when swimming will be found 1-3 m below the surface. In warm seasons they usually occur alone or in pairs, although larger groups have been observed, especially in areas where there are good conditions for feeding or resting.
Manatees require fresh water for drinking and so will be found in areas such as creeks where fresh water is available. Sea grass is their primary food source and adults may spend hours grazing at a time. In between feeding the manatee will rest suspended at the surface or on the bottom of the water that it is in. Due to a low metabolic rate, manatees find it difficult to thermoregulate and as a consequence are susceptible to mortality in cold temperatures. To overcome this, West Indian manatees will aggregate in large groups in areas of warm water during periods of cold weather.
Florida manatees undertake extensive seasonal migrations with distribution determined by water temperature. When ambient water temperatures drop below 20°C (68°F) in autumn and winter, manatees will aggregate at natural and artificial warm-water refuges or move to southern Florida with most manatees returning to the same warm-water refuges each year. Manatees can be found in very shallow water, as shallow as 0.4 m with their backs out of the water but are usually found in deeper water and when swimming will be found 1-3 m below the surface. In warm seasons they usually occur alone or in pairs, although larger groups have been observed, especially in areas where there are good conditions for feeding or resting.
The West Indian manatee is found in shallow rivers, canals, saltwater bays, estuaries, lagoons and coastal areas. Because of their extremely low metabolic rate and absence of a thick layer of insulating body fat, they prefer to stay in water that is more than 20oC but can endure temperatures as low as 13.50C.
Florida manatees (T. m. latirostris) are found only in the United States, although a few have been known to migrate as far as the Bahamas. Their year-round distribution is restricted to peninsular Florida because where they bcan find warm water to over winter in. During the non-winter months (March to November), some manatees disperse to adjoining states.
The Antillean Manatee (T. m. manatus) inhabits riverine and coastal systems in the tropical and subtropical areas from the Bahamas to Brazil, including the Caribbean Sea and Gulf of Mexico. During the past decade, populations have been confirmed in the coastal waters and/or rivers of at least 19 of the 37 countries with historical records.
The Antillean Manatee (T. m. manatus) inhabits riverine and coastal systems in the tropical and subtropical areas from the Bahamas to Brazil, including the Caribbean Sea and Gulf of Mexico. During the past decade, populations have been confirmed in the coastal waters and/or rivers of at least 19 of the 37 countries with historical records.
Both subspecies are estimated to number less than 2,500 mature individuals.
Decreasing.
Classified as Vulnerable (VU C1) on the 2010 IUCN Red List of Threatened Species.
The greatest threat to the West Indian manatee in Florida is collisions with watercraft such as boats and jet skis which happen frequently in the densely populated coastal regions and accounts for 35% of known causes of death. The disturbance caused by water activities may also be disrupting the behaviour of manatees which in turn may be detrimental to their health or survival. In addition to boat strikes, manatees can also be come trapped and crushed in water control devices such as flood control structures or caught in fishing equipment. Loss and destruction of the warm water habitats in which the Florida manatee aggregates is also cause for concern for a species so vulnerable to cold water mortality. Declines in warm water habitats and water quality are directly linked to the increasing human population.
The threats to the Antillean manatee are the same as those faced by the Florida manatee with the additional threat of hunting, which occurs less frequently than in the past but is still considered as a significant threat in some central American countries. Pollution of coastal areas is also frequently reported and presents a threat to the quality of habitat in which the West Indian Manatee is found.
The threats to the Antillean manatee are the same as those faced by the Florida manatee with the additional threat of hunting, which occurs less frequently than in the past but is still considered as a significant threat in some central American countries. Pollution of coastal areas is also frequently reported and presents a threat to the quality of habitat in which the West Indian Manatee is found.
In all countries where the West Indian manatee is present there is protective legislation and some conservation effort. In general conservation measures largely include protective legislation, management plans, recovery plans, and community management as well as educational programmes that aim to promote awareness and conservation.
Legislation that prohibits the killing of the Florida population of West Indian Manatee has been in place since 1893. Further federal measures are aimed at conserving the Florida populations of the West Indian manatee by introducing boat speed restrictions and safe havens for the manatee. Manatee protection devices are also being developed to reduce the number of manatees that become trapped or crushed when gates in water control structures close. Habitat protection and public education are further measures being used to promote the conservation of the species and maintain the habitats in which it is found.
Conservation of the Antillean manatee at a regional level has been driven by the SPAW (Specially Protected Areas and Wildlife) Protocol to the Cartagena Convention, which has resulted in the Regional Management Plan for the West Indian Manatee which is the product of a joint collaboration between the United Nations Environment Programme (UNEP) and Caribbean Environment Programme (CEP).
Legislation that prohibits the killing of the Florida population of West Indian Manatee has been in place since 1893. Further federal measures are aimed at conserving the Florida populations of the West Indian manatee by introducing boat speed restrictions and safe havens for the manatee. Manatee protection devices are also being developed to reduce the number of manatees that become trapped or crushed when gates in water control structures close. Habitat protection and public education are further measures being used to promote the conservation of the species and maintain the habitats in which it is found.
Conservation of the Antillean manatee at a regional level has been driven by the SPAW (Specially Protected Areas and Wildlife) Protocol to the Cartagena Convention, which has resulted in the Regional Management Plan for the West Indian Manatee which is the product of a joint collaboration between the United Nations Environment Programme (UNEP) and Caribbean Environment Programme (CEP).
Since this species crosses boarders it is important that there is regional co-operation to conserve it. Key recommendations proposed by the Regional Management Plan include assessment of the West Indian manatee population size and distribution, defined survey guidelines, environmental education and enforcement of legislation. It is important that the manatees' habitats are conserved, particularly the warm-water aggregation sites that allow them to tolerate drops in temperature without being forced to migrate large distances. Further development of detection tools that could be used by shipping traffic in the Florida area may also be valuable in reducing the number of fatalities in the region.
Deutsch, C.J., Self-Sullivan, C. & Mignucci-Giannoni, A. 2008. Trichechus manatus. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4. <www.iucnredlist.org>. Downloaded on 15 November 2010.
Hartman, D. S. (1979). Ecology and Behaviour of the Manatee (Trichechus manatus) in Florida. Special Publication No. 5. The American Society of Mammalogists
Haubold, E.M. et al. 2006. Final biological status review of the Florida manatee (Trichechus manatus latirostris) Status Assessment by the 2005-2006 Florida Manatee Biological Review Panel.
Nowak, R.M. 1999. Walker’s mammals of the world. Volume 2. Johns Hopkins University Press, Baltimore and London. p992.
UNEP: Regional Management Plan for the West Indian Manatee (Trichechus manatus) compiled by Ester Quintana-Rizzo and John Reynolds III. CEP Technical Report No. 48. UNEP Caribbean Environment Programme, Kingston, Jamaica. 2010
Hartman, D. S. (1979). Ecology and Behaviour of the Manatee (Trichechus manatus) in Florida. Special Publication No. 5. The American Society of Mammalogists
Haubold, E.M. et al. 2006. Final biological status review of the Florida manatee (Trichechus manatus latirostris) Status Assessment by the 2005-2006 Florida Manatee Biological Review Panel.
Nowak, R.M. 1999. Walker’s mammals of the world. Volume 2. Johns Hopkins University Press, Baltimore and London. p992.
UNEP: Regional Management Plan for the West Indian Manatee (Trichechus manatus) compiled by Ester Quintana-Rizzo and John Reynolds III. CEP Technical Report No. 48. UNEP Caribbean Environment Programme, Kingston, Jamaica. 2010
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