Trichechus manatus latirostris

North American Manatee

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North American Manatee

 

Description

The Florida manatee is a long-lived marine mammal, dark gray in color, and averaging about 10 feet (3 m) in length and between 800 and 1,200 pounds (363 to 544 kg) in weight. It has a round, flattened, paddle-shaped tail and two front flippers that are used for steering while swimming (Federal Register, 75 FR 1574-1579).

Geography

Florida manatees constitute the largest known group of West Indian manatees anywhere in the species’ range. Outside the United States, manatees occur in the Greater Antilles, on the east coast of Mexico and Central America, along the north and northeastern coast of South America, and in Trinidad (Lefebvre et al. 2001, cited in USFWS 2001).

In the southeastern United States, manatees occur primarily in Florida and southeastern Georgia, but individuals can range as far north as Chesapeake Bay or even Rhode Island on the Atlantic coast, and probably as far west as Texas on the Gulf coast (USFWS 2001). In summer, is now not uncommon to find manatees in coastal waters of Georgia, North and South Carolina, Alabama, and Louisiana (Federal Register, 75 FR 1574-1579).

 

Ecosystem

The Florida manatee lives in freshwater, brackish, and marine habitats, including coastal tidal rivers and streams, mangrove swamps, salt marshes, and freshwater springs. Submerged, emergent, and floating vegetation are their preferred foods. During the winter, cold temperatures keep the population concentrated in peninsular Florida and many manatees rely on the warm water from natural springs and power plant outfalls. During the summer they expand their range and on rare occasions are seen as far north as Rhode Island on the Atlantic coast and possibly as far west as Texas on the Gulf coast (USFWS 2001, 2007).

The following summary of habitat use by the Florida manatee is based on the review in the West Indian Manatee 5-Year Review (USFWS 2007 and references therein): Shallow grass beds, with ready access to deep channels, are generally preferred feeding areas in coastal and riverine habitats. In coastal Georgia and northeastern Florida, manatees feed in salt marshes on smooth cordgrass (Spartina alterniflora) by timing feeding periods with high tide. Manatees use springs and freshwater runoff sites for drinking water; secluded canals, creeks, embayments, and lagoons for resting, cavorting, mating, calving and nurturing their young; and open waterways and channels as travel corridors. Manatees occupy different habitats during various times of the year, with a focus on warm-water sites during winter. Manatees have adapted to changing ecosystems in Florida. Industrial warm-water discharges and deep-dredged areas are used as wintering sites, stormwater/freshwater discharges provide manatees with drinking water, and the imported exotic plant, Hydrilla sp. (which has replaced native aquatic species in some areas), has become an important food source at wintering sites.

 

Historically, manatees relied on the warm, temperate waters of south Florida and on natural warm-water springs scattered throughout Florida as buffers against the lethal effects of cold winter temperatures. In part, as a result of human disturbance at natural sites, they have expanded their winter range to include industrial sites and associated warm-water discharges as refuges from the cold. Although manatees overwinter at major springs throughout peninsular Florida, nearly two-thirds of the population winters at industrial warmwater sites, which are now made up almost entirely of power plants.

 

 

 

 

Conservation

The Florida manatee subspecies is listed as Endangered on the basis of a population size of less than 2,500 mature individuals and the population is estimated to 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.

 

Threats

The most significant problem presently faced by Florida manatees is death or injury from boat strikes (USFWS 2001; 2007 and references therein), both direct impacts and propeller cuts. Collisions with watercraft accounted for an average of 24% of known manatee deaths in Florida annually (1976-2000), with 30% in 1999 and 29% in 2000. The second major concern is the long-term availability of warm-water refuges for manatees, which is uncertain if minimum flows and levels are not established for the natural springs on which many manatees depend, and as deregulation of the power industry in Florida occurs (manatees take advantage of warm power plant outfalls) (USFWS 2001; 2007 and references therein). Deaths attributed to water control structures and navigational locks (e.g., entrapment and crushing in gates or locks) represents 4% of known deaths (USFWS 2001) and other threats, such as entanglement in fishing gear, appear to be relatively minor.

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