manatee n : sirenian mammal of tropical coastal waters of America; the flat tail is rounded [syn: Trichechus manatus]

English

Etymology

Spanish manatí, from a Carib language.

Pronunciation

globalize article Manatees (family.. Trichechidae, genus Trichechus) are large, fully aquatic marine mammals sometimes known as sea cows. The name manatí comes from the Taino which are the original peoples of the Caribbean, meaning "breast". They comprise three of the four living species in the order Sirenia, the other being the dugong, which is native to the Eastern Hemisphere. The Sirenia is thought to have evolved from four-legged land mammals over 60 million years ago, with the closest living relatives being the Proboscidea (elephants) and Hyracoidea (hyraxes).

Physical characteristics

The manatees differ from the dugong. Dugongs have a forked tail, similar in shape to a whale's, while manatees' tails are paddle-shaped. They are mainly herbivores, spending most of their time grazing in shallow waters and at depths of 1-2 metres (3-7 ft). Much of the knowledge about manatees is based upon research done in Florida and cannot necessarily be attributed to all types of manatees. Generally, manatees have a mean mass of 400-550 kg (900-1200 lb), and mean length of 2.8-3.0 m (9-10 ft), with maximums of 3.6 meters and 1,775 kg seen (the females tend to be larger and heavier). When born, baby manatees have an average mass of 30 kg.

On average, most manatees swim at about 5 km/h to 8 km/h (1.4 m/s to 2.2 m/s; 3 to 5 miles per hour). However, they have been known to swim up to 30 km/h (8 m/s; 20 miles per hour) in short bursts. Manatees inhabit the shallow, marshy coastal areas and rivers of the Caribbean Sea and the Gulf of Mexico (T. manatus, West Indian manatee), the Amazon basin (T. inunguis, Amazonian manatee), and West Africa (T. senegalensis, West African manatee). A fourth species, the dwarf manatee (T. bernhardi) was recently proposed for a population found in the Brazilian Amazon, although some have questioned its validity, instead believing it is an immature Amazonian manatee. Florida is usually the northernmost range of the West Indian manatee as their low metabolic rate makes cold weather endurance difficult. They may on occasion stray up the mid-Atlantic coast in summer. Half a manatee's day is spent sleeping in the water, surfacing for air regularly at intervals no greater than 20 minutes.

Florida manatees (T. m. latirostris) have been known to live up to 60 years, and they can move freely between different salinity extremes; however, Amazonian manatees (T. inunguis) never venture out into salt water. They have a large flexible prehensile upper lip that acts in many ways like a shortened trunk, somewhat similar to an elephant's. They use the lip to gather food and eat, as well as using it for social interactions and communications. Their small, widely spaced eyes have eyelids that close in a circular manner. Manatees are also believed to have the ability to see in color.

They emit a wide range of sounds used in communication, especially between cows and their calves, yet also between adults to maintain contact and during sexual and play behaviors. They may use taste and smell, in addition to sight, sound, and touch, to communicate. Manatees are capable of understanding discrimination tasks, and show signs of complex associated learning and advanced long term memory. They demonstrate complex discrimination and task-learning similar to dolphins and pinnipeds in acoustic and visual studies.

Diet

Manatees are herbivores and eat over 60 different plant species such as mangrove leaves, turtle grass, and types of algae, using their divided upper lip. An adult manatee will commonly eat up to 9% of its body weight (approx 50 kg) per day. Manatees have been known to eat small amounts of fish from nets.

Like horses, they have a simple stomach, but a large cecum, in which they can digest tough plant matter. In general, their intestines are unusually long for animals of their size. The adults have no incisor or canine teeth, just a set of cheek teeth, which are not clearly differentiated into molars and premolars. Uniquely among mammals, these teeth are continuously replaced throughout life; with new teeth growing at the rear as older teeth fall out from further forward in the mouth. At any given time, a manatee typically has no more than six teeth. In 2006 there were near 300 registered and confirmed manatees in Florida killed by human activity, the majority of these, that happened to be discovered by Florida Fish and Wildlife, have been caused by boat strikes.

Accurate population estimates of the Florida manatee are notoriously difficult and have been called scientifically weak, with widely varying counts from year to year, some areas showing possible increases yet others with decreases, but with very little strong evidence of increases except in 2 areas. However, population viability analysis studies carried out in 1997, found that decreasing adult survival and eventual extinction is a probable future outcome for the Florida manatees, unless they are aggressively protected. Manatee counts are highly variable without an accurate way to estimate numbers, for example, in Florida in 1996, a winter survey found 2,639 manatees, in 1997 a January survey found 2,229, but then a February survey found 1,709.

Manatees often congregate near power plants, which warm the waters. Some have become reliant on this source of artificial heat and have ceased migrating to warmer waters. Some power plants have recently been closing and the U.S. Fish and Wildlife Service is trying to find a new way to heat the water for these manatees. The main water treatment plant in Guyana has four manatees that keep storage canals clear of weeds.

Studies in Florida suggest that Florida manatees must have some access to fresh water for proper osmoregulation.

Captivity

The oldest manatee in captivity is Snooty who is held at the South Florida Museum. He was born at the Miami Seaquarium on July 21 1948 and came to the South Florida Museum in Bradenton, Florida in 1949.

Vulnerability

Manatees are slow-moving, non-aggressive, and generally curious creatures. They enjoy warmer waters and are known to congregate in shallow waters, and frequently migrate through brackish water estuaries to freshwater springs.

Their slow-moving, curious nature, coupled with dense coastal development, has led to a number of violent collisions with propellers from fast moving recreational motor boats, leading frequently to maiming, disfigurement, and even death. As a result, a large portion of manatees exhibit propeller scars on their backs and they are now even classed by humans from their scar patterns. Some are concerned that the current situation is inhumane, with sometimes upwards of 50 scars and disfigurations from boat strikes on a single manatee. Often the cuts lead to infections, which can prove fatal. Internal injuries stemming from hull impacts have also been fatal.

In 2003, a population model was released by the U.S. Geological Survey that predicted an extremely grave situation confronting the manatee in both the Southwest and Atlantic regions where the vast majority of manatees are found. It states, “In the absence of any new management action, that is, if boat mortality rates continue to increase at the rates observed since 1992, the situation in the Atlantic and Southwest regions is dire, with no chance of meeting recovery criteria within 100 years.”

In 2007, a University of Florida study found that more than half of boat drivers in Volusia County, Florida sped through marked conservation zones despite their professed support for the endangered animals, and little difference was found between the driving speeds of ski boats, pontoons and fishing vessels. In the study, 84 percent of the 236 people who responded said they fully obeyed with speed limits in manatee zones during their most recent boating experience, but observers found that only 45 percent actually complied. "Hurricanes, cold stress, red tide poisoning and a variety of other maladies threaten manatees, but by far their greatest danger is from watercraft strikes, which account for about a quarter of Florida manatee deaths," said study curator John Jett.

Cultural depictions

The manatee has been linked to folklore on mermaids. Native Americans ground the bones to treat asthma and earache. In West African folklore, it was sacred and thought to have been once human. Killing one was taboo and required penance.

See also

• USS Manatee (AO-58)
• Evolution of sirenians

Notes

References

External links

• Reuters: Florida manatees may lose endangered status
• A website with many manatee photos
• A coalition of scientists studying and saving manatees around the world
• USGS gallery on manatees
• A website dedicated to helping save the manatee
• Some more information on manatees
• Report on Florida manatees by primary school students

nah:Tlācamichin