Manatee
Manatees are large, fully aquatic, mostly herbivorous marine mammals sometimes known as sea cows. There are three accepted living species of Trichechidae, representing three of the four living species in the order Sirenia: the Amazonian manatee, the West Indian manatee, and the West African manatee. They measure up to long, weigh as much as, and have paddle-like tails.
Manatees are herbivores and eat over 60 different freshwater and saltwater plants. Manatees inhabit the shallow, marshy coastal areas and rivers of the Caribbean Sea, the Gulf of Mexico, the Amazon basin, and West Africa.
The main causes of death for manatees are human-related issues, such as habitat destruction and human objects. Their slow-moving, curious nature has led to violent collisions with propeller-driven boats and ships. Some manatees have been found with over 50 scars on them from propeller blades. Natural causes of death include adverse temperatures, predation by crocodiles on young, and disease.
Etymology
The etymology of the name is unclear, with connections having been made to Latin manus "hand" and to the term manaty "breast" from the Carib language of native South Americans. The Carib term may refer to the mammary glands of the manatee, which are located on their chests under their armpits. The term sea cow is a reference to the species' slow, peaceful, herbivorous nature, reminiscent of that of bovines. Lamantin was commonly used as an alternative name until the 20th century.Taxonomy
Manatees are three of the four living species in the order Sirenia. The fourth is the Eastern Hemisphere's dugong. The Sirenia are thought to have evolved from four-legged land mammals more than 60 million years ago, with the closest living relatives being the Proboscidea and Hyracoidea.Description
Manatees weigh, and average in length, sometimes growing to and and females tend to be larger and heavier than males. At birth, baby manatees weigh about each. The female manatee has two teats, one under each flipper, a characteristic that was used to make early links between the manatee and elephants.The lids of manatees' small, widely spaced eyes close in a circular manner. The manatee has a large, flexible, prehensile upper lip, used to gather food and eat and for social interaction and communication. Manatees have shorter snouts than their fellow sirenians, the dugongs.
Manatee adults have no incisor or canine teeth, just a set of cheek teeth, which are not clearly differentiated into molars and premolars. These teeth are repeatedly replaced throughout life, with new teeth growing at the rear as older teeth fall out from farther forward in the mouth, somewhat as elephants' teeth do. At any time, a manatee typically has no more than six teeth in each jaw of its mouth.
The manatee's tail is paddle-shaped, and is the clearest visible difference between manatees and dugongs; a dugong tail is fluked, similar in shape to that of a whale.
The manatee is unusual among mammals in having just six cervical vertebrae, a number that may be due to mutations in the homeotic genes. All other mammals have seven cervical vertebrae, other than the two-toed and three-toed sloths.
Like the horse, the manatee has a simple stomach, but a large cecum, in which it can digest tough plant matter. Generally, the intestines are about 45 meters, unusually long for an animal of the manatee's size.
Evolution
Fossil remains of manatee ancestors - also known as sirenians - date back to the Early Eocene. It is thought that they reached the isolated area of the South American continent and became known as Trichechidae. In the Late Miocene, trichechids were likely restricted in South American coastal rivers and they fed on many freshwater plants. Dugongs inhabited the West Atlantic and Caribbean waters and fed on seagrass meadows instead. As the sea grasses began to grow, manatees adapted to the changing environment by growing supernumerary molars. Sea levels lowered and increased erosion and silt runoff was caused by glaciation. This increased the tooth wear of the bottom-feeding manatees.Behavior
Apart from mothers with their young, or males following a receptive female, manatees are generally solitary animals. Manatees spend approximately 50% of the day sleeping submerged, surfacing for air regularly at intervals of less than 20 minutes. The remainder of the time is mostly spent grazing in shallow waters at depths of. The Florida subspecies has been known to live up to 60 years.Locomotion
Generally, manatees swim at about. However, they have been known to swim at up to in short bursts.Intelligence and learning
Manatees are capable of understanding discrimination tasks and show signs of complex associative learning. They also have good long-term memory. They demonstrate discrimination and task-learning abilities similar to dolphins and pinnipeds in acoustic and visual studies. Social interactions between manatees are highly complex and intricate, which may indicate higher intelligence than previously thought, although they remain poorly understood by science.Reproduction
Manatees typically breed once every two years; generally only a single calf is born. Gestation lasts about 12 months and to wean the calf takes a further 12 to 18 months, although females may have more than one estrous cycle per year.Communication
Manatees emit a wide range of sounds used in communication, especially between cows and their calves. Their ears are large internally but the external openings are small, and they are located four inches behind each eye. Adults communicate to maintain contact and during sexual and play behaviors. Taste and smell, in addition to sight, sound, and touch, may also be forms of communication.Diet
Manatees are herbivores and eat over 60 different freshwater and saltwater plants. Using their divided upper lip, an adult manatee will commonly eat up to 10–15% of their body weight per day. Consuming such an amount requires the manatee to graze for up to seven hours a day. To be able to cope with the high levels of cellulose in their plant based diet, manatees utilize hindgut fermentation to help with the digestion process. Manatees have been known to eat small numbers of fish from nets.Feeding behavior
Manatees use their flippers to "walk" along the bottom whilst they dig for plants and roots in the substrate. When plants are detected, the flippers are used to scoop the vegetation toward the manatee's lips. The manatee has prehensile lips; the upper lip pad is split into left and right sides which can move independently. The lips use seven muscles to manipulate and tear at plants. Manatees use their lips and front flippers to move the plants into the mouth. The manatee does not have front teeth, however, behind the lips, on the roof of the mouth, there are dense, ridged pads. These horny ridges, and the manatee's lower jaw, tear through ingested plant material.Dentition
Manatees have four rows of teeth. There are 6 to 8 high-crowned, open-rooted molars located along each side of the upper and lower jaw giving a total of 24 to 32 flat, rough-textured teeth. Eating gritty vegetation abrades the teeth, particularly the enamel crown; however, research indicates that the enamel structure in manatee molars is weak. To compensate for this, manatee teeth are continually replaced. When anterior molars wear down, they are shed. Posterior molars erupt at the back of the row and slowly move forward to replace these like enamel crowns on a conveyor belt, similarly to elephants. This process continues throughout the manatee's lifetime. The rate at which the teeth migrate forward depends on how quickly the anterior teeth abrade. Some studies indicate that the rate is about 1 cm/month although other studies indicate 0.1 cm/month.Ecology
Range and habitat
Manatees inhabit the shallow, marshy coastal areas and rivers of the Caribbean Sea and the Gulf of Mexico, the Amazon basin, and West Africa.West Indian manatees prefer warmer temperatures and are known to congregate in shallow waters. They frequently migrate through brackish water estuaries to freshwater springs. They cannot survive below 15 °C. Their natural source for warmth during winter is warm, spring-fed rivers.
West Indian
The coast of the state 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 below 20 °C can cause "cold stress syndrome" and death.West Indian manatees can move freely between fresh water and salt water. However, studies suggest that they are susceptible to dehydration if freshwater is not available for an extended period of time.
Manatees can travel hundreds of miles annually, and have been seen as far north as Cape Cod, and in 1995 and again in 2006, one was seen in New York City and Rhode Island's Narragansett Bay. A manatee was spotted in the Wolf River harbor near the Mississippi River in downtown Memphis in 2006, and was later found dead downriver in McKellar Lake. Another manatee was found dead on a New Jersey beach in February 2020, considered especially unusual given the time of year. At the time of the manatee's discovery, the water temperature in the area was below 6.5 °C.
The West Indian manatee migrates into Florida rivers—such as the Crystal, the Homosassa, and the Chassahowitzka rivers, whose headsprings are 22 °C all year. Between November and March each year, about 600 West Indian manatees gather in the rivers in Citrus County, Florida such as the Crystal River National Wildlife Refuge.
In winter, manatees often gather near the warm-water outflows of power plants along the Florida coast, instead of migrating south as they once did. Some conservationists are concerned that these manatees have become too reliant on these artificially warmed areas.
Accurate population estimates of the West Indian manatee in Florida are difficult. They have been called scientifically weak because they vary widely from year to year, with most areas showing decreases, and 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, the highest number recorded to that time.
As of January 2016, the USFWS estimates the range-wide West Indian manatee population to be at least 13,000; as of January 2018, at least 6,100 are estimated to be in Florida.
Population viability studies conducted in 1997 found that decreasing adult survival and eventual extinction were probable future outcomes for Florida manatees unless they received more protection. The U.S. Fish and Wildlife Service proposed downgrading the manatee's status from endangered to threatened in January 2016 after more than 40 years.
There is a small population of the subspecies Antillean manatee found in Mexico's Caribbean coastal area. The best estimate for this population is 200-250. As of 2022, a new manatee habitat was discovered by Klaus Thymann within the cenotes of Sian Ka'an Biosphere Reserve on the Yucatán Peninsula. The explorer and his team documented the discovery with a 12-minute film that is available on the interactive streaming platform WaterBear. The discovery got picked up by the New Scientist in 2024, who featured in a 10-minute short film.