Manatees (/ˈmænətiːz/,familyTrichechidae,genusTrichechus) are large, fully aquatic, mostlyherbivorousmarine mammals sometimes known assea cows. There are three accepted living species of Trichechidae, representing three of the four living species in the orderSirenia: theAmazonian manatee (Trichechus inunguis), theWest Indian manatee (Trichechus manatus), and theWest African manatee (Trichechus senegalensis). They measure up to 4.0 metres (13 ft 1 in) long, weigh as much as 590 kilograms (1,300 lb),[2] and have paddle-like tails.
The main causes of death for manatees are human-related issues, such ashabitat 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 toLatinmanus "hand" and to the termmanaty "breast" from theCarib language of native South Americans.[3] The Carib term may refer to the mammary glands of the manatee, which are located on their chests under their armpits.[4][5] The termsea cow is a reference to the species' slow, peaceful, herbivorous nature, reminiscent of that ofbovines.[6]Lamantin (from Frenchlamantin) was commonly used as an alternative name until the 20th century.[7]
Taxonomy
Manatees are three of the four living species in the orderSirenia. The fourth is theEastern Hemisphere'sdugong. The Sirenia are thought to have evolved from four-legged land mammals more than 60 million years ago, with the closest living relatives being theProboscidea (elephants) and Hyracoidea (hyraxes).[8]
Description
A skeleton of a manatee and calf, theMuseum of Osteology,Oklahoma CitySkull of a West Indian manatee, the Museum of Osteology, Oklahoma City
Manatees weigh 400 to 550 kg (880 to 1,210 lb), and average 2.8 to 3.0 m (9 ft 2 in to 9 ft 10 in) in length, sometimes growing to 4.6 m (15 ft 1 in) and 1,775 kg (3,913 lb) and females tend to be larger and heavier than males. At birth, baby manatees weigh about 30 kg (66 lb) each. The female manatee has two teats, one under each flipper,[9] 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 fellowsirenians, thedugongs.
Manatee adults have noincisor orcanine teeth, just a set of cheek teeth, which are not clearly differentiated intomolars andpremolars. These teeth arerepeatedly replaced throughout life, with new teeth growing at the rear as older teeth fall out from farther forward in the mouth, somewhat aselephants' teeth do.[10][11] At any time, a manatee typically has no more than six teeth in each jaw of its mouth.[11]
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.
Like thehorse, the manatee has a simple stomach, but a largececum, 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.[15]
Evolution
Fossil remains of manatee ancestors - also known assirenians - date back to theEarly Eocene.[16][17] It is thought that they reached the isolated area of the South American continent and became known asTrichechidae. In theLate 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 onseagrass 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 byglaciation. This increased the tooth wear of the bottom-feeding manatees.[18]
Behavior
Endangered Florida manatee (Trichechus manatus)
Apart from mothers with their young, or males following a receptive female, manatees are generally solitary animals.[11] 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 1–2 m (3 ft 3 in – 6 ft 7 in). TheFlorida subspecies (T. m. latirostris) has been known to live up to 60 years.
Locomotion
Generally, manatees swim at about 5 to 8 km/h (3 to 5 mph). However, they have been known to swim at up to 30 km/h (20 mph) in short bursts.[19]
Intelligence and learning
Manatee postures in captivity
Manatees are capable of understanding discrimination tasks and show signs of complexassociative learning. They also have goodlong-term memory.[20] They demonstrate discrimination and task-learning abilities similar todolphins andpinnipeds inacoustic and visual studies.[21] Social interactions between manatees are highly complex and intricate, which may indicate higher intelligence than previously thought, although they remain poorly understood by science.[22]
Reproduction
Manatees typically breed once every two years; generally only a single calf is born.Gestation lasts about 12 months and towean the calf takes a further 12 to 18 months,[11] although females may have more than oneestrous cycle per year.[23]
Communication
Manatees emit a wide range of sounds used in communication, especially between cows and their calves.[24] Their ears are large internally but the external openings are small, and they are located four inches behind each eye.[25] 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.[26]
Diet
Manatees areherbivores and eat over 60 different freshwater (e.g., floating hyacinth,pickerel weed,alligator weed,water lettuce,hydrilla, water celery,musk grass,mangrove leaves) and saltwater plants (e.g., sea grasses,shoal grass,manatee grass,turtle grass,widgeon grass, sea clover, and marine algae).[27][28] Using their divided upper lip, an adult manatee will commonly eat up to 10%–15% of their body weight (about 50 kg) per day. Consuming such an amount requires the manatee to graze for up to seven hours a day.[29] 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.[30] Manatees have been known to eat small numbers of fish from nets.[31]
Feeding behavior
Manatee plate
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 hasprehensile 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.[29]
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 toelephants. 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.[29]
West Indian manatees prefer warmer temperatures and are known to congregate in shallow waters. They frequently migrate throughbrackish waterestuaries tofreshwatersprings. They cannot survive below 15 °C (60 °F). Their natural source for warmth during winter is warm, spring-fed rivers.
West Indian
The coast of the state ofGeorgia is usually the northernmost range of the West Indian manatees because their lowmetabolic rate does not protect them in cold water. Prolonged exposure to water below 20 °C (68 °F) can cause "cold stress syndrome" and death.[33]
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.[34]
Manatees can travel hundreds of miles annually,[35] and have been seen as far north asCape Cod, and in 1995[36] and again in 2006, one was seen in New York City[37] andRhode Island'sNarragansett Bay. A manatee was spotted in theWolf River harbor near theMississippi River in downtown Memphis in 2006, and was later found dead 16 km (10 mi) downriver in McKellar Lake.[38] Another manatee was found dead on a New Jersey beach in February 2020, considered especially unusual given the time of year.[39] At the time of the manatee's discovery, the water temperature in the area was below 6.5 °C (43.7 °F).[40]
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.[42]
Accurate population estimates of the West Indian manatee in Florida are difficult. They have been called scientifically weak[43] 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.[21] A statewide synoptic survey in January 2010 found 5,067 manatees living in Florida, the highest number recorded to that time.[44]
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.[45][46]
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.[47] 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.[48]
There is a small population of the subspeciesAntillean manatee (T. m. manatus) found in Mexico's Caribbean coastal area. The best estimate for this population is 200-250.[49] As of 2022, a new manatee habitat was discovered byKlaus Thymann within the cenotes ofSian Ka'an Biosphere Reserve on theYucatán Peninsula. The explorer and his team documented the discovery with a 12-minute film that is available on the interactive streaming platform WaterBear.[50] The discovery got picked up by theNew Scientist in 2024, who featured in a 10-minute short film.[51]
Amazonian
The freshwater Amazonian manatee (T. inunguis) inhabits the Central Amazon Basin inBrazil, easternPerú, southeasternColombia, but notEcuador. It is the only exclusively freshwater manatee, and is also the smallest. Since they are unable to reduce peripheral heat loss, it is found primarily in tropical waters.[52]
West African
They are found in coastal marine and estuarine habitats, and in freshwater river systems along the west coast of Africa from theSenegal River south to theCuanza River inAngola. They live as far upriver on theNiger River asKoulikoro inMali, 2,000 km (1,200 mi) from the coast.[53]
Predation
In relation to the threat posed by humans,predation does not present a significant threat to manatees.[16] When threatened, the manatee's response is to dive as deeply as it can, suggesting that threats have most frequently come from land dwellers such as humans rather than from other water-dwelling creatures such ascaimans or sharks.[16]
Young manatees can be curious; this individual is inspecting akayak.
The main causes of death for manatees are human-related issues, such as habitat destruction and human objects. Natural causes of death include adverse temperatures, predation by crocodiles on young, and disease.[54]
Ship strikes
Their slow-moving, curious nature, coupled with dense coastal development, has led to many violent collisions with propeller-driven boats and ships, leading frequently to maiming, disfigurement, and even death. As a result, a large proportion of manatees exhibit spiral cutting propeller scars on their backs, usually caused by larger vessels that do not haveskegs in front of the propellers like the smaller outboard and inboard-outboard recreational boats have. They are now even identified by humans based on their scar patterns. Many manatees have been cut in two by large vessels like ships and tug boats, even in the highly populated lower St. Johns River's narrow channels. Some are concerned that the current situation is inhumane, with upwards of 50 scars and disfigurements from vessel strikes on a single manatee.[55] Often, the lacerations lead to infections, which can prove fatal. Internal injuries stemming from being trapped between hulls and docks and impacts have also been fatal. Testing and studies from the 2000s and 2010s suggested that manatees may be able to hear speed boats and other watercraft approaching, due to the frequency the boat makes.[56][57] However, a manatee may not be able to hear the approaching boats when they are performing day-to-day activities or distractions. The manatee has a tested frequency range of 8 to 32 kilohertz.[56]
Manatees hear on a higher frequency than would be expected for such large marine mammals. Many large boats emit very low frequencies, which confuse the manatee and explain their lack of awareness around boats. TheLloyd's mirror effect results in low frequency propeller sounds not being discernible near the surface, where most accidents occur. Research indicates that when a boat has a higher frequency the manatees rapidly swim away from danger.[58]
In 2003, a population model was released by theUnited States Geological Survey that predicted an extremely grave situation confronting the manatee in both the Southwest and Atlantic regions where the vast majority of manatees are found. It states,
In the absence of any new management action, that is, if boat mortality rates continue to increase at the rates observed since 1992, the situation in the Atlantic and Southwest regions is dire, with no chance of meeting recovery criteria within 100 years.[59] "Hurricanes, cold stress, red tide poisoning and a variety of other maladies threaten manatees, but by far their greatest danger is from watercraft strikes, which account for about a quarter of Florida manatee deaths," said study curator John Jett.[60]
Manatee bearing scars on its back from a boat propeller.
The severity of mutilations for some of these individuals can be astounding – including long term survivors with completely severed tails, major tail mutilations, and multiple disfiguring dorsal lacerations. These injuries not only cause gruesome wounds, but may also impact population processes by reducing calf production (and survival) in wounded females – observations also speak to the likely pain and suffering endured.[21] In an example, they cited one case study of a small calf "with a severe dorsal mutilation trailing a decomposing piece of dermis and muscle as it continued to accompany and nurse from its mother ... by age 2 its dorsum was grossly deformed and included a large protruding rib fragment visible."[21]
These veterinarians go on to state:
[T]he overwhelming documentation of gruesome wounding of manatees leaves no room for denial. Minimization of this injury isexplicit in the Recovery Plan, several state statutes, and federal laws, andimplicit in our society's ethical and moral standards.[21]
One quarter of annual manatee deaths in Florida are caused by boat collisions with manatees.[61] In 2009, of the 429 Florida manatees recorded dead, 97 were killed by commercial and recreational vessels, which broke the earlier record number of 95 set in 2002.[62][63]
In 1996, a red tide was responsible for 151 manatee deaths in Florida.[65] The bloom was present from early March to the end of April and killed approximately 15% of the known population of manatees along South Florida's western coast.[66] Other blooms in 1982 and 2005 resulted in 37 and 44 deaths respectively,[67] and a red tide killed 123 manatees between November 2022 and June 2023.[68]
Starvation
In 2021 a massive die-off ofseagrass along theAtlantic coast ofFlorida left manatees without enough food to eat, and they began dying at high rates.[69] TheU.S. Fish and Wildlife Service responded with a feeding program that distributing 3,000 pounds (1,361 kg) oflettuce per day to the manatee population.[70]
Additional threats
Manatees can also be crushed and isolated in water control structures (navigation locks,floodgates, etc.) and are occasionally killed by entanglement in fishing gear, such ascrab pot float lines, box traps, and shark nets.[53]
While humans are allowed to swim with manatees in one area of Florida,[71] there have been numerous charges of people harassing and disturbing the manatees.[72] According to the United States Fish and Wildlife Service, approximately 99 manatee deaths each year are related to human activities.[73] In January 2016, there were 43 manatee deaths in Florida alone.[74]
All three species of manatee are listed by theWorld Conservation Union as vulnerable to extinction. However, TheU.S. Fish and Wildlife Service (FWS) does not consider the West Indian manatee to be "endangered" anymore, having downgraded its status to "threatened" as of March 2017. They cite improvements to habitat conditions, population growth and reductions of threats as reasoning for the change. The reclassification was met with controversy, with Florida congressmanVern Buchanan and groups such as the Save the Manatee Club and theCenter for Biological Diversity expressing concerns that the change would have a detrimental effect on conservation efforts.[75] The new classification will not affect current federal protections.[45] West Indian manatees were originally classified as endangered with the 1967 class of endangered species.[76]
Manatee deaths in the state of Florida nearly doubled in 2021 from 637 (2020) to 1100.[77] Although this number decreased to 800 in 2022, it is likely that current rate of development in Florida, climate change, and decreasing water quality, habitat range, and genetic diversity among this population may lead to reconsideration of the West Indian Manatee as an endangered species.[78] Manatee population in the United States reached a low in the 1970s, during which only a few hundred individuals lived in the nation.[79] As of February 2016, 6,250 manatees were reported swimming in Florida's springs.[80] It is illegal under federal and Florida law to injure or harm a manatee.
Also in Florida, due to extensive destruction of their habitat, manatees rely on the warm waters created by a major power plant's hot water effluent streams to survive during the cold winter months. Manatee reliance on these effluent streams is such that the streams are protected under federal environmental legislation. Researchers have theorized that the prevalence of manatee sightings near this power plant is contributing to "collective inattention" to industrialization and development as ongoing causes of manatee habitat destruction.[81][82]
There are many conservation programs that have been created to help manatees.Save the Manatee Club is a non-profit group and membership organization that works to protect manatees and their aquatic ecosystems. Founded byBob Graham, former Florida governor, and singer/songwriterJimmy Buffett, this is today's leading manatee conservation club.[83][self-published source?]
Brazil outlawed hunting in 1973 in an effort to preserve the species. Deaths by boat strikes are still common.[84][85] Although countries are protecting Amazonian manatees in the locations where they are endangered, as of 1994 there were no enforced laws, and the manatees were still being captured throughout their range.[86]
The Columbus Zoo was a founding member of the Manatee Rehabilitation Partnership in 2001. Since 1999, the zoo's Manatee Bay facility has helped rehabilitate 20 manatees.[88] The Cincinnati Zoo has rehabilitated and released more than a dozen manatees since 1999.[89]
The oldest manatee in captivity wasSnooty,[92] at theSouth Florida Museum's Parker Manatee Aquarium inBradenton, Florida. Born at the Miami Aquarium and Tackle Company on July 21, 1948, Snooty was one of the first recorded captive manatee births. Raised entirely in captivity, Snooty was never to be released into the wild. As such he was the only manatee at the aquarium, and one of only a few captive manatees in the United States that was allowed to interact with human handlers. That made him uniquely suitable for manatee research and education.[93]
Snooty died suddenly two days after his 69th birthday, July 23, 2017, when he was found in an underwater area only used to access plumbing for the exhibit life support system. The South Florida Museum's initial press release stated, "Early indications are that an access panel door that is normally bolted shut had somehow been knocked loose and that Snooty was able to swim in."[94]
The manatee has been linked to folklore onmermaids.[84] InWest African folklore, they were considered sacred and thought to have been once human. Killing one wastaboo and required penance.[98] In the cosmogony of theSerer people of Senegal, Gambia, and Mauritania, the cayman and the manatee holds great significance inSerer mythology. The cayman is believed to hold the secrets of the past whilst the manatee holds the secrets of the future.[99]
In the novelMoby-Dick,Herman Melville distinguishes manatees ("Lamatins", cf.lamantins) from small whales; stating, "I am aware that down to the present time, the fish styled Lamatins andDugongs (Pig-fish and Sow-fish of theCoffins of Nantucket) are included by many naturalists among the whales. But as these pig-fish are a noisy, contemptible set, mostly lurking in the mouths of rivers, and feeding on wet hay, and especially as they do not spout, I deny their credentials as whales; and have presented them with their passports to quit the Kingdom ofCetology."[100]
InRudyard Kipling'sThe White Seal (one of the stories inThe Jungle Book), Sea Cow, about whom the story says that he has only six cervical vertebrae, is a manatee.
The manatees Friends West Indian Manatee, Dugong, and Steller's Sea Cow appear in multipleKemono Friends games, including the app version of Kemono Friends 3.[102][103][104]
In the Neapolitan region of Italy, a culinary legend exists around the consumption of manatees duringWorld War II. In the story, when Naples andSalerno surrended to the Allies in 1943, the cities, lacking food supplies thanked the Allied generals by serving manatee from the aquarium. When this was revealed, the popular reaction was not shock, but questions over how it was prepared, to which the answer was "aglio-olio [garlic and olive oil], of course, with a little parsley."[105]
^Domning, D.P., 1994, "Paleontology and evolution of sirenians: Status of knowledge and research needs", inProceedings of the 1st International Manatee and Dugong Research Conference, Gainesville, Florida, 1–5
^abcMarsh, H. (2011).Ecology and Conservation of the Sirenia: Dugongs and Manatees. O'Shea, Thomas J., Reynolds III, John E. Cambridge: Cambridge University Press.ISBN978-1-139-15887-9.OCLC782876868.
^Gerstein, E. R. (1994). "The manatee mind: Discrimination training for sensory perception testing of West Indian manatees (Trichechus manatus)".Marine Mammals.1:10–21.
^US Fish and Wildlife Service (November 14, 2017)."About the Refuge".Crystal River National Wildlife Refuge, Florida. Archived fromthe original on October 30, 2020. RetrievedJanuary 28, 2020.
^"Abary Creek manatees under threat".Stabroek News. 30 September 2008. Retrieved16 June 2020.there are 23 manatees [...] between the Botanical Gardens and the National Park. They have been there for more than 129 years, and reports are that they came from theAbary Creek.[dead link]
^National Research Council (2002).Making Aquatic Weeds Useful. The Minerva Group. p. 35.ISBN978-0-89499-180-6.In the Georgetown Water and Sewerage Works, two manatees [...] were introduced in 1952 to a canal [...] In the 24 years since then, manatees have been used to keep this water (the city's municipal supply) weed-free.
^Cooper, JC (1992).Symbolic and Mythological Animals. London: Aquarian Press. p. 157.ISBN1-85538-118-4.
^Senghor, Léopold Sédar, "Chants d'ombre" [in] "Selected poems of LEOPOLD SEDAR SENGHOR", CUP Archive, pp. 103, 125
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