14 DAY TRIAL // 1.European sailors navigating, a few centuries ago, in tropical waters could not believe their eyes: they were seeing mermaids, common in the sea folklore. The creature were fish-like from the waist beyond, had a pair of breasts in the chest area, and their flippers and heads vaguely resembled human head and arms from a distance. What they were seeing were in fact manatees and dugongs from the order Sirenia (literally meaning "mermaids").
They are sea mammals whose closest relatives are the ... elephants! Generically, they are also called sea cows. They can be found living solitary or in groups.
There is only one species of dugong, living on the shores of eastern Africa, southern Asia, northern Australia and New Guinea. There are three manatee species: Western Indies manatee from southeastern US, northern South America and Caribbean, West African manatee from western coast of Africa (from Senegal to Angola, entering into the Senegal Rive) and Amazon manatee found exclusively in the Amazon River and its affluents.
Dugongs have blunt muzzles and dolphin-like Tails, while manatees have rounded muzzles and rounded tails. Manatees lack tusks, while dugongs have a pair of short tusks. The skin of the sea cows is folded and wrinkled.
Dugongs are up to 4 m (13 ft) long and weigh 230-900 kg (500-2,000 pounds) while manatees are 2.5-4.6 m (8-15 ft) long, weighing 350-1,600 kg (800-3.500 pounds) (the Amazon manatee is smaller).
All sea cows, except the Amazon manatee, live in estuaries and coastal waters. The dugongs feel better in a more marine environment and can depart to long distances from the shore, while manatees rarely stay away from freshwater, and can be found far upward on the rivers.
The Amazon manatee isolated in Pliocene (2-5 MA), when the raising of the Andes changed the flow of the Amazon, which previously had been running into the Pacific, to the Atlantic. They cannot tolerate saltwater.
2.These animals are unique as being the only herbivorous sea mammals. They move slowly through shallow warm water, conserving energy and grazing the rhizomes of sea weeds, rich in sugars. Amazon manatee consumes especially plants floating on the water's surface. Dugongs are known to feed during the night in shallow waters on patches of sea grass. Unfortunately, plants moved to another place warn the hunters about the place where the dugongs are found.
The upper lip of the sea cows is cleaved and each half moves independently.
Manatees depose energy as fat under the skin. Even in tropical waters, it can be cold and the fat is isolating. The fat helps them to survive shortage periods: Amazon manatee must stand without food six months during the dry season, when water plants are hard to find.
During chilly mornings, manatees hang vertically in the water exposing out of the water just their snouts and bringing gradually to the water surface the rest of the body, while the external temperature is rising. Manatees can get ill when water temperature drops under 21o C. That's why, in Florida, they look, between December and March, for natural thermal springs in the coast areas.
The dense bones of the sea cows serve as ballast while feeding in the water. They dig in the sediment with the fore limbs for extracting the deeply rooted vegetation and they are seen sometimes carrying in their "arms" piles of plants.
3.Besides the small tusk of the dugongs, sea cows have only back teeth, used for grinding plant food. Because many of their food plants contain abrasive sand, the manatees' teeth constantly move forward with 1 mm monthly. As the teeth reach the front line, they fall and are replaced by new ones. This way, the manatees always have functional teeth.
4.Life family of the dugongs is less known, as they are extremely shy and live in murky waters. Dugongs can be spotted alone or in groups up to 100 individuals.
Manatees live in free groups that can change continuously, as they make frequent short journeys and seasonal migrations. They are tame and often enter in contact one with each other by touching their muzzles in a "kiss". Both sexes rub their genitalia and other body parts on underwater "rubbing places", leaving behind a chemical signal which marks their presence. When a female is sexually receptive, up to 12 males can gather around her.
5.Females give birth to one calf after one year of gestation. The calves start eating vegetation at the age of several weeks, but are fed with milk till they have 18 months. They remain with their mothers at least 2 years, learning the migration routes from and to good feeding places.
Females are sexually mature by the age of 8-18 years, and live up to 50 years, but they do not have more than 6 calves along their lifespan.
6.Most dugong and manatee populations have been exterminated, as "mermaid" meat is considered a delicacy. The manatee meat is cooked in its own fat and this way it remains fresh for months. That's why hundreds of thousands of manatees were killed during the 17th century and their meat was sent to Europe. When they turned hard to find, this trade ceased, but local hunt kept on going. Today, all species of sea cows are endangered.
The sale of the meat of Amazon manatee is forbidden and fishermen accidentally entangling manatees are encouraged to release them immediately. Five natural reserves on the Amazon contain protected manatees feeding in the flooded forest during the rainy season.
7.Manatees cannot detect objects moving with over 50 km (30 mi) per hour. That's why they cannot avoid motorboats and many of them got killed or mutilated by them. 25 % of the Florida's manatees die because of this. Florida's manatees are already endangered, and in 2006 at least 75 manatees have been killed in collisions with watercrafts, according to the Florida Fish and Wildlife Conservation Commission.
Recent studies show the animals to hear well enough to avoid boat accidents and that's why scientists are puzzled of why manatees keep getting hit. They may be hit while sleeping during surfacing to breathe, or they may have gotten accustomed to the sound of boats.
Manatees and dugongs have tiny eyes and the brain region corresponding to sight is small compared to the auditory and tactile ones, but they seem to see color, a very unusual trait for marine mammals. As manatees have very poor eyesight, in many cases they bump into underwater objects.
However, they seem to rely on touch sense: the muzzle and body are covered with 3,000 special sensory hairs all over their body, unlike most mammals, which just have whiskers. Each hair is connected to 50 nervous terminations (in humans, to maximum 5). Together these tactile hairs form a sensory array, possibly allowing manatees to detect changes in current, underwater objects, water temperature, and even tidal forces. Slight pressure on the hairs indicates to the manatee the arrival of the tide for swimming on the right direction, but also to keep a safety distance from other manatees. A similar system would be found in the lateral line of the fish, using another type of receptors.
If diving in manatees' water you see one of these huge "mermaids" approaching to give you what it looks like a kiss, do not panic! Researchers have recently found a unique sense of touch in these animals: they can "touch at a distance" - an ability to "feel" objects and events in the water from relatively far away.
Manatees' brain area dedicated to touching is "especially large", even larger than in animals known to be particularly sensitive feelers, like star-nosed moles. For a manatee puckering up for a diver, that's just the animal's way of collecting information by spreading out the hairs around its mouth to sense what it's approaching. The facial hairs are actively exploring the environment around manatees.
This bizarre sense explains how manatees are able to make long and convoluted migrations in murky waters, where vision is of no use, like the impressive journey made by manatees in a mazelike network of waterways called Ten Thousand Islands, near Naples, Florida. Manatees make daily journeys through the watery labyrinth, leaving the rivers each morning to forage in the large beds of sea grass offshore before swimming back at night. They seem to use their tactile hairs that are all over their bodies to detect the movement of water and, when they are in the environment, like a navigational tool. When a hurricane is coming, they get out of the area, but nobody can say what sense they use for this.
8.In Brazil, reservoirs have been successfully populated with manatees, which consume floating vegetation. If allowed to proliferate, these plants impede light penetrating the water, causing the death of fitoplankton, the base food for fish. Without the manatees, the oxygen poor stagnant waters accumulate hydrogen sulfide (H2S) formed by the immense amounts of decomposing vegetation, which deteriorates the turbines of the hydro-centrals.
9.Till the 17th century, there was a fifth species of sea cow, called Steller's sea cow. It was huge compared to living species: 8 m (26 ft) long, and weighed at least 4 tones. The animals went extinct in only 30 years after being discovered by the Europeans!
10.Manatee's brain, small (orange sized for an animal as big as a cow) and smooth, made researchers regard these animals as being not very intelligent and incapable to fulfill difficult tasks. But some researchers have uncovered that manatees are actually much smarter than previously thought.
Far from being slow learners, manatees seem to be as adept at experimental tasks as dolphins, though they are slower-moving and more difficult to motivate. In lab experiments made in Florida, when a buzzer sounds, a captive manatee learned to aim the right loudspeaker from eight ones lowered into the water when it sounded, in order to receive treats.
These herbivorous mammals are so slow moving due to their size, they have no natural threats to confront and, also, they conserve the energy gotten from their poor diet.
