West Indian manatee

WestIndianManatee.jpg

West Indian manatee: Trichechus manatus

Taxonomic Classification

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Sirenia
Family: Trichechidae
Genus/Species: Trichechus manatus
Common Name: West Indian manatee

The subspecies of the West Indian manatee (Trichechus manatus) that occurs in Florida is also known as the Florida manatee (Trichechus manatus latirostris).

Listing Status

Federal Status: Endangered
FL Status: Federally-designated Endangered
FNAI Ranks: G2/S2 (Imperiled)
IUCN Status: VU (Vulnerable)

Physical Description

The West Indian manatee is a large gray aquatic mammal that commonly reaches a body length of nine to ten feet (2.7-3 meters) and a weight of 1,000 pounds (453.6.6 kilograms); however, it can grow to more than 13 feet (four meters) and weight up to 3,500 pounds (1587.6 kilograms).  Manatees feature a wide rounded tail and two flipper-like fore limbs that have three to four nails.  Flippers are used to maneuver in the water and to grasp vegetation while feeding.  The nostrils are located above the snout and have valves that tightly close when the manatee is under water.  Their small eyes have a membrane that can cover the eyes for protection.  The ear openings are small and external lobes are lacking.  Manatees have a flexible lip pad that is used to move food into their mouth.  Manatees have back teeth (molars) for chewing but no frontal teeth.  Teeth are continuously lost and re-grown throughout the manatee’s life.  Molars form at the back of the jaw and slowly progress to the front of the jaw where they will fall out.  This is seen as an adaptation trait for feeding on vegetation with sand mixed in.  Manatees can hold their breath up to 20 minutes when resting, but when active they surface to breath every three to five minutes. 

Life History

The diet of the manatee primarily consists of marine and freshwater vegetation (ex. Syringodium filaforme) (Bester, n.d.).  This species feeds between six and eight hours a day, eating up to ten percent of its body weight in vegetation. 

Manatees can breed and give birth throughout the year; however, birthing usually peaks in the spring.  During the breeding season, males gather and pursue a female to form a mating group and breed at different times (Bester, n.d.).  The gestation time for the manatee is 13 months.  Manatees have a low reproductive rate, only giving birth to an average of one calf every three to five years.  Females give birth to their first calf between the ages of four and seven years old (Marmontel 1995; O'Shea and Hartley 1995; Rathbun et al., 1995).  The calf will stay with the mother for up to two years. 

Habitat and Distribution

West Indian Manatee Distribution Map

The West Indian manatee can be found along coasts and inland waters of the southeastern United States, eastern Mexico, the Greater Antilles (Hispaniola, Cuba, Puerto Rico, Jamaica), and Central America down to as far as northern Brazil.

Threats:

The main threats to manatees are boat collisions and the loss of warm water habitat.  Manatees feed in shallow waters making them susceptible to interactions with boats.  Boat related deaths can be caused by propeller cuts, impacts from the hull or lower unit of the motor, or a combination of the two.  Large ships can crush manatees on the bottom of waterways or between the vessel and the wharf.  Impact related and crushing injuries cause various lethal internal injuries.  Due to the inability to regulate their body temperature (thermoregulate) in cold water, cold stress is a serious threat to the manatee (Irvine 1983).  The loss of warm water refuges is seen as a serious long-term threat to the continued existence of the manatee (U.S. Fish & Wildlife Service 2001).  Habitat loss is also an issue as coastal development and pollution can destroy seagrass beds and freshwater aquatic vegetation, which is the main food source of manatees.  Manatees are also at risk of becoming entangled in monofilament line (fishing line) and crab trap lines which lead to injury, rescues, and death in extreme cases.  Periodically, manatees will get crushed in flood gates and canal locks, or trapped in culverts where they drown or starve.  Other threats include diseases, natural disasters, and red tide.  Red tide is a dramatic increase of the Karenia brevis algae, which can be a danger to many marine species. 

Conservation and Management

The West Indian manatee is protected as an Endangered species by the Federal Endangered Species Act and as a Federally-designated Endangered species by Florida’s Endangered and Threatened Species Rule External Website.  It is also protected by the U.S. Marine Mammal Protection Act and the Florida Manatee Sanctuary Act (FMSA).  The FMSA allows the State to set restrictions on boat speed and access in important manatee habitats.  FWC enforces these boating restrictions along with Federal and local government partners.

State Management Plan Adobe PDF
Federal Recovery Plan External Website

Other Informative Links

FWC Manatee Research
FWC Petitions and Listing Actions
FWC Species Profile
International Union for Conservation of Nature External Website
U.S. Fish and Wildlife Service Species Information External Website
U.S. Geological Survey External Website

 

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References

Bester, C. (n.d.). West Indian manatee. Retrieved August 1, 2011,   from Icthyology: http://www.flmnh.ufl.edu/fish/southflorida/seagrass/manatee.html External Website

Irvine, A.B. 1983. Manatee metabolism and its influence on distribution in Florida. Biological Conservation 25:315-334.

Marmontel, M. 1995. Age and reproduction in female Florida manatees. Pp. 98-119 in T.J. O'Shea, B.B. Ackerman, and H.F. Percival, eds., Population Biology of the Florida Manatee (Trichechus manatus latirostris). National Biological Service, Information and Technology Report 1. 289 pp.

O'Shea, T.J., and W.C. Hartley. 1995. Reproduction and early age survival of manatees at Blue Spring, Upper St. Johns River, Florida. Pages 157-170 in T.J. O’Shea, B.B. Ackerman, and H.F. Percival, editors. Population biology of the Florida manatee. National Biological Service Information and Technology Report 1. Washington, D.C. 289pp.


Image Credit Photo by FWC



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