Trichechus manatus

The West Indian manatee (Trichechus manatus) or 'sea cow', also known as American manatee, is the largest surviving member of the aquatic mammal order Sirenia (which also includes the dugong and the extinct Steller's sea cow). The West Indian manatee is a species distinct from the Amazonian manatee (T. inunguis) and the African manatee (T. senegalensis). Based on genetic and morphological studies, the West Indian manatee is divided into two subspecies, the Florida manatee (T. m. latirostris) and the Antillean or Caribbean manatee (T. m. manatus). However, recent genetic (mtDNA) research suggests that the West Indian manatee actually consists of three groups, which are more or less geographically distributed as: (1) Florida and the Greater Antilles; (2) Mexico, Central America and northern South America; and (3) northeastern South America. The West Indian Manatee was placed on the Endangered Species List in the 1970s, when there were only several hundred left, and it has been of great conservation concern to federal, state, private, and nonprofit organizations to protect these species from natural and human-induced threats like collisions with boats. On March 30, 2017, the US Secretary of the Interior Ryan Zinke announced the federal reclassification of the manatee from endangered to threatened as the number of sea cows had increased to over 6,000. The average West Indian manatee is about 2.7–3.5 m (8.9–11.5 ft) long and weighs 200–600 kg (440–1,320 lb), with females generally larger than males. The difference between the two subspecies of the West Indian manatee is that the Florida manatee is commonly reported as being larger in size compared to Antillean manatee. The largest individual on record weighed 1,655 kg (3,649 lb) and measured 4.6 m (15 ft) long. Since manatees are mammals, they breathe air, have warm blood, have hair, and give birth to live young. Like the other sirenians, the West Indian manatee has adapted fully to aquatic life, having no hind limbs. Instead of hind limbs, the manatee has a spatula-like paddle for propulsion in the water. Manatees have evolved streamlined bodies which lack external ear flaps, thus decreasing resistance in the aquatic environment. Pelage cover is sparsely distributed across the body, which may play a role in reducing the build-up of algae on their thick skin. Manatee skin is gray but can vary in coloration due to algae and other biota, like barnacles, that opportunistically live on manatees. Scar tissue on manatees is white and persists for decades, allowing for easy identification. The Florida manatee has three to four nails on each flipper. Nails are absent in the Amazonian manatee. The West Indian manatee has a prehensile snout, like their relative the elephant, for grabbing vegetation and brining it into their mouths. Manatees have six to eight moliform teeth in each jaw quadrant. These moliform teeth are generated at the back of the mouth and slowly migrate towards the front of the mouth, at a rate of 1-2 mm per month, where they then fall out. This tooth ‘conveyor belt’ provides unlimited tooth production which is beneficial for the manatee which feeds on vegetation four to eight hours per day and consumes 5-10% of its body weight per day. Manatees have 3-5 cm hairs that cover their whole body and provide somatosensory information. Manatee bones are dense and solid which allows them to act as ballast and promote negative buoyancy. This helps counteract the positive buoyancy which comes from their high fat content. These two buoyancy counterparts, along with air in the lungs, helps manatees achieve neutral buoyancy in the water. This makes breathing, foraging, and swimming easier for the manatee. Manatees are unique, compared to other mammals, in that they have a longitudinally oriented diaphragm that is spit in half to form two hemidiaphragms. Each hemidiaphragm is capable of independent muscular contractions. As its name implies, the West Indian manatee lives in the West Indies, or Caribbean, generally in shallow coastal areas. However, it is known to withstand large changes in water salinity, so has also been found in shallow rivers and estuaries. It can live in fresh, brackish, and saline water. It is limited to the tropics and subtropics due to an extremely low metabolic rate and lack of a thick layer of insulating body fat. While this is a regularly occurring species along coastal southern Florida, during summer, this large mammal has even been found as far north as Dennis, Massachusetts, and as far west as Texas. A manatee was spotted in the Wolf River (near where it enters the Mississippi) in Memphis, Tennessee in 2006. The Florida manatee (Trichechus manatus latirostris), a subspecies of the West Indian manatee, is the largest of all living sirenians. Florida manatees inhabit the most northern limit of sirenian habitats. Over three decades of research by universities, governmental agencies, and NGOs have contributed to understanding of Florida manatee ecology and behavior. They are found in freshwater rivers, in estuaries, and in the coastal waters of the Gulf of Mexico and the Atlantic Ocean. Florida manatees may live to be more than 28 years old in the wild, and one captive manatee, 'Snooty', lived for 69 years.