West Indian
The coast of Georgia is usually the northernmost range of the West Indian manatees because their low metabolic rate does not protect them in cold water. Prolonged exposure to water temperatures below 68 °F (20 °C) can bring about "cold stress syndrome" and death.
Florida manatees can move freely between salinity extremes.
Manatees have been spotted as far north as Cape Cod, and as recently as the late summer of 2006, one was seen in New York City and Rhode Island's Narragansett Bay, as cited in The Boston Globe. According to Memphis, Tennessee's The Commercial Appeal newspaper, one manatee was spotted in the Wolf River harbor near the Mississippi River in downtown Memphis, Tennessee, on October 23, 2006, though it was later found dead ten miles downriver in McKellar Lake.
The West Indian manatee migrates into Florida rivers, such as the Crystal, the Homosassa, and the Chassahowitzka Rivers. The headsprings of these rivers maintain a 22°C (72°F) temperature year round. During November to March, approximately 400 West Indian manatees (according to the National Wildlife Refuge) congregate in the rivers in Citrus County, Florida.
During the winter months, manatees often congregate near the warm water outflows of power plants along the coast of Florida instead of migrating south as they once did, causing some conservations to worry they have become too reliant on these artificially-warmed areas. The U.S. Fish and Wildlife Service is trying to find a new way to heat the water for manatees that are dependent on plants that have closed. The main water treatment plant in Guyana has four manatees that keep storage canals clear of weeds; there are also some in the ponds of the National Park in Georgetown, Guyana.
Studies suggest Florida manatees must have some access to fresh water for proper osmoregulation.
Accurate population estimates of the Florida manatee (T. manatus) are notoriously difficult and have been called scientifically weak; with widely varying counts from year to year, some areas show increases and others decreases, with very little strong evidence of increases except in two areas. Manatee counts are highly variable without an accurate way to estimate numbers:in Florida in 1996, a winter survey found 2,639 manatees; in 1997, a January survey found 2,229; and a February survey found 1,706. A statewide synoptic survey in January 2010 found 5,067 manatees living in Florida, which is a new record count.
Population viability studies carried out in 1997 found that decreasing adult survival and eventual extinction is a probable future outcome for Florida manatees, without additional protection.
Fossil remains of Florida manatee ancestors date back about 45 million years.
Read more about this topic: Manatee, Ecology, Range and Habitat
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