Global distribution map for the three extant species of manatees. The range of the West Indian manatee is shown in blue/red (Florida subspecies in blue, Antillean in red); Amazonian manatee in yellow; and West African manatee in green. Image credit: Gonzalez-Socoloske, D. (2012). Gentle Giants in Dark Waters: Using Side-Scan Sonar for Manatee Research. The Open Remote Sensing Journal, 5(1), 1–14. https://doi.org/10.2174/1875413901205010001. Image CC-BY 4.0.
Manatees are large, aquatic mammals found in marine, brackish, and freshwater systems throughout coastal and riverine areas of the southeastern U.S., eastern Mexico, Central America, northern South America, the Caribbean Islands, and West Africa. They use their paddle-like front flippers and highly maneuverable muscular lips to grasp plants and spend up to eight hours a day grazing on seagrasses and other aquatic vegetation.
There are three extant manatee species: the West Indian (Trichechus manatus spp.), African (Trichechus senegalensis), and Amazonian manatee (Trichechus inunguis). The Amazonian manatee is the largest freshwater mammal in South America, but it is the smallest of the manatee species. Adults weigh up to 500 kg (1,100 lb) and measure up to 3 m (9.8 ft) in body length. The Amazonian manatee is endemic to the Amazon River Basin of northern South America and is found exclusively in freshwater. Distribution of the Amazonian manatee is associated with seasonal floods of the Amazon River. During low water periods some manatee populations are restricted to deeper parts of lakes. Large fat reserves and low metabolic rates allow Amazonian manatees to survive for many months with little to no food.
African manatees are listed as vulnerable by the International Union for Conservation of Nature (IUCN), facing extinction due to poaching, accidental fisheries capture, and habitat degradation. Because of elusive behavior and poor water clarity, passive acoustic methods are used to detect African manatees.
Most African manatee vocalizations are detected during nighttime hours. Like other manatee species, African manatees produce vocalizations with multiple harmonics. These vocalizations have a reported fundamental frequency centered at 4.65 kHz, frequency band ranges from 2 to 8 kHz, and a duration of 0.04-0.4 s. Although their vocalizations are like those of other manatee species, there are subtle differences. The mean fundamental frequency of African manatee calls is higher and the mean call duration is shorter compared to other manatee species.