Many scientists believe that sirenians evolved around fifty-five million years ago from small hoofed animals. The closests living relatives today are elephants and small asian mammals called hyraxes. Although there are vast differences between elephants, hyraxes, and sirenians, fossil evidence shows that all three evolved from a common ancestor. The manatee’s physical characteristics are visible remnants of their ancient heritage. The dugong’s tusks are another link to elephants. Like elephants, sirenians are enormous animals. There are five species of Sirenia, but scientists theorize that there were many more in the past.
Early forms of manatees are thought to have originated near the Amazon basin in South America. Some remained there to become the Amazonian manatee, while others migrated up through the Caribbean, giving rise to the Antillean and Florida manatees. Another group managed to swim or where carried on currents across the Atlantic and became the West African manatee. Dugongs thought to have evolved along with mantees once ranged from Europe to Africa, and along the East and West coasts of the Americas. At the present time, they are only found in the Eastern Hemisphere in the Indian and Pacific Oceans.
Steller’s Sea Cow, another species of Sirenian became extinct by fisherman within 25 to 30 years of its discovery in the 1700’s. Physical Characteristics An adult manatee has a rounded body, usually light to dark gray or black, that tapers to a horizontally flattened, rounded tail, which provides propulsion and also serves as a rudder. Manatee’s range in length from 8 to 14 ft. long, depending on the species and can weigh 440 to 1300lbs. Although males can grow larger than the females. The small head includes a straight snout and a cleft upper lip with bristly hairs.
Whiskers can be found on the surface of the lips, each attached seperatly to nerve endings and its own blood supply in the follicle. A manatees only teeth are 24 to 32 molars located in the back of the mouth, in addition to molars, manatees have horny, ridged pads at the front of the upper and lower jaws. The manatees upper lip is cleft with two lobes this isn used for gathering food. There small eyes are located on the sides of the head. Its nostrils, set on the upper surface of the snout are closed tightly by valves when the animal is under water.
Their lungs and diagphram run lengthwise along the body, unlike other mammals, in which they run crosswise. This supposedly provides balance in the water. The many muscles surrounding the lungs allow manatees to exspel air more rapidly than other animals, thus making it possible for them to submerge for up to 15 minutes at a time. The paddlike fore limbs are set close to the head; no external limbs exists. The minimal amount of body hair and lack of hind limbs and external ears all reduce friction when the manatee glides threw the water. Habitat
Manatees inhabit shallow, marshy coastal areas of North, Central and South America and the Caribbean Sea. The Florida manatee primarly reside in Florida’s coastal waters during winter and migrate either as far north as the Carolinas or as far west as Louisiana during the summer months. It can also survive in both fresh and salt water. Manatees live in small family groups, although they do travel in herds of 15 to 20. Sirenians are the only aquatic mammals that are primarily vegetarians. They are considered herbivores and feed in both fresh and saltwater.
They eat over 60 species of plants and forage on seagrass beds in bays, estuaries, and coastal rivers and graze for six to eight hours a day. An adult consumes an amount equal to between 5 and 10 percent of its body weight daily. Manatees have a slower metabolism than other mammals of similar size, which sharply reduces there energy requirements. Manatees ingest snails and other small animals found on and among the seagrasses on which they feed. The shells of these creatures provide calcium and phosphorus which the manatees require. There are also reports of them occasionally feeding on fish.
This deviation from their vegetarian diet may be an important source of protein. In captivity, manatees need supplemental minerals to remain healthy. Conservation of the Manatee Manatees are not predators themselves, and there are no animals that prey on them except for man and possibly sharks. It is this dependence on vegetation near the shore that makes manatees so vulnerable to human-caused death. These doscile creatures were heavily exploited in the 19th and early 20th century, their hides made for leather, their bones worked like ivory, and their delectable meat eaten. Efforts to protect manatees began many years ago.
Manatees have been protected by Florida Law since 1893 and federal law since 1972, but poaching continued into the 1980’s. Some of the main causes of death for the manatees are boaters, barges, pneumonia, red tide and the most seriuos long-term threat is a loss of habitats. There has been considerable loss of the grass flats where manatees feed. Manatees populations are now considered stable, but increasing at a small rate over a period of time can be disasterious. The main reason for there nongrowing population here in Florida is because they are very slow are reproducing.
A female manatee must be at least 4 to 6 years old before she can have her first calf, and generally have only one at a time and then usually does not have another for about two to five years. The total population of manatees in florida alone is small. There may be as many as 2,000 or fewer than 1,000, depending on the source, and there numbers are probably declining slowly. They live well over 30 years in captivity, but no one knows what age they might attain in the wild. Their natural life span is probably as much as 60 to 70 years. Conclusion
All experts agree that there is still much to learn about habitat protection, planning, law enforcement and education of the Sirenians. As for current priorities in programs to save sirenians, particulary the manatees in Florida, one of the major needs appears to be better coordination and cooperation among the many organizations and agencies involved. But among all the problems the biggest faced today is funding. Research, conservation of habitat, rescue and rehabilitation of injured and sick animals, and everything else that is necessary to protect sirenians from possible extinction, is expensive.
Even though experts are concerned about the future of the sirenians, they say on the positive side, the large amount of information and data gathered by several organizations and agencies could be put to better use by expanded and improved use of the geographic Information System(GIS) capabilities. But overall, most agree that following the laws concerning the protection of these creatures, maintaining there habitats and less human contact while in there natural environment will ensure that the manatee population will remain for many more years to come.