The West Indian manatee (''Trichechus manatus''), also known as the North American manatee, is a large, aquatic mammal native to warm coastal areas of the Caribbean, from the
Eastern United States
The Eastern United States, often abbreviated as simply the East, is a macroregion of the United States located to the east of the Mississippi River. It includes 17–26 states and Washington, D.C., the national capital.
As of 2011, the Eastern ...
to northern Brazil. Living alone or in herds, it feeds on underwater plants and uses its whiskers to navigate. It is divided into two subspecies, the Florida manatee (''T. m. latirostris'') in the United States and the Antillean manatee (''T. m. manatus'') in the Caribbean, both of which are endangered and face pressure from habitat loss, pollution, and other human activity. The West Indian manatee is the largest living member of the
sirenia
The Sirenia (), commonly referred to as sea cows or sirenians, are an order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. The extant Sirenia comprise two distinct famili ...
ns (order Sirenia), a group of large aquatic mammals that includes the
dugong
The dugong (; ''Dugong dugon'') is a marine mammal. It is one of four living species of the order Sirenia, which also includes three species of manatees. It is the only living representative of the once-diverse family Dugongidae; its closest ...
, other
manatee
Manatees (, family (biology), family Trichechidae, genus ''Trichechus'') are large, fully aquatic, mostly herbivory, herbivorous marine mammals sometimes known as sea cows. There are three accepted living species of Trichechidae, representing t ...
s, and the extinct
Steller's sea cow
Steller's sea cow (''Hydrodamalis gigas'') is an extinction, extinct sirenian described by Georg Wilhelm Steller in 1741. At that time, it was found only around the Commander Islands in the Bering Sea between Alaska and Russia; its range exte ...
.
Manatees are
herbivore
A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat ...
s, have developed vocal communication abilities, and are covered in highly sensitive whiskers (called
vibrissae) that are used for feeding and navigation.
In breeding season, several males form mating herds around an individual female; on average, one calf is born to a female manatee every two to three years.
In the 1970s, the West Indian manatee was listed as "endangered" in the United States under the
Endangered Species Act
The Endangered Species Act of 1973 (ESA; 16 U.S.C. § 1531 et seq.) is the primary law in the United States for protecting and conserving imperiled species. Designed to protect critically imperiled species from extinction as a "consequence of e ...
, when there were only several hundred left.
The decades since have witnessed significant efforts to protect this species from natural and human threats, particularly collisions with
watercraft
A watercraft or waterborne vessel is any vehicle designed for travel across or through water bodies, such as a boat, ship, hovercraft, submersible or submarine.
Types
Historically, watercraft have been divided into two main categories.
*Raf ...
. In 2017, the United States changed the classification to "threatened", citing a substantial increase in the total population''.
''
Description
The average West Indian manatee is about long and weighs , with females generally larger than males. The largest individual on record weighed and measured long. Manatees are estimated to live 50 years or more in the wild,
and one captive Florida manatee,
Snooty, lived for 69 years (1948–2017).

Given that manatees are
mammal
A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...
s, they breathe air, have warm blood, and produce milk. Like the other
sirenian
The Sirenia (), commonly referred to as sea cows or sirenians, are an order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. The extant Sirenia comprise two distinct famili ...
s, 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
A fur is a soft, thick growth of hair that covers the skin of almost all mammals. It consists of a combination of oily guard hair on top and thick underfur beneath. The guard hair keeps moisture from reaching the skin; the underfur acts as an ...
cover is sparsely distributed across the body, which may play a role in reducing the build-up of
algae
Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...
on their thick skin. Manatee skin is gray but can vary in coloration due to algae and other biota, like
barnacle
Barnacles are arthropods of the subclass (taxonomy), subclass Cirripedia in the subphylum Crustacean, Crustacea. They are related to crabs and lobsters, with similar Nauplius (larva), nauplius larvae. Barnacles are exclusively marine invertebra ...
s, 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.
[Reep, R. L. & Bonde, R. K. (2006). ''The Florida manatee: Biology and conservation''. Gainesville: The University Press of Florida.]
The West Indian manatee has a prehensile snout, like their relative the
elephant
Elephants are the largest living land animals. Three living species are currently recognised: the African bush elephant ('' Loxodonta africana''), the African forest elephant (''L. cyclotis''), and the Asian elephant ('' Elephas maximus ...
, for grabbing vegetation and bringing it into their mouths. Manatees have six to eight
molariform teeth in each jaw quadrant. These molariform 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
Ballast is dense material used as a weight to provide stability to a vehicle or structure. Ballast, other than cargo, may be placed in a vehicle, often a ship or the gondola of a balloon or airship, to provide stability. A compartment within ...
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 split in half to form two hemidiaphragms. Each hemidiaphragm is capable of independent muscular contractions.
Distribution and habitat
The West Indian manatee inhabits mostly shallow coastal areas, including
river
A river is a natural stream of fresh water that flows on land or inside Subterranean river, caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of ...
s and
estuaries
An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...
. Manatees can withstand large changes in
salinity
Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensio ...
and are found in both freshwater and saltwater.
Manatees' extremely low metabolic rate and lack of a thick layer of
insulating body fat limits them to locations with warm waters, including tropical regions.
The Florida subspecies is primarily found along the Florida coast, but has been spotted as far north as
Dennis, Massachusetts
Dennis is a New England town, town in Barnstable County, Massachusetts, Barnstable County, Massachusetts, United States, located near the center of the Cape Cod, Cape Cod peninsula. It is a seaside resort town with colonial mansions along the nor ...
, as well as along the
Gulf Coast of Texas. Concerning their forays inland, a manatee was once spotted in the
Wolf River (near where it enters the Mississippi) in
Memphis, Tennessee
Memphis is a city in Shelby County, Tennessee, United States, and its county seat. Situated along the Mississippi River, it had a population of 633,104 at the 2020 United States census, 2020 census, making it the List of municipalities in Tenne ...
, in 2006: a distance of over 700 river miles from the Gulf of Mexico. The Antillean subspecies has a sparse distribution throughout the
Caribbean
The Caribbean ( , ; ; ; ) is a region in the middle of the Americas centered around the Caribbean Sea in the Atlantic Ocean, North Atlantic Ocean, mostly overlapping with the West Indies. Bordered by North America to the north, Central America ...
, ranging as far north as
Mexico
Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...
and as far south as
Brazil
Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...
.
During the
Pleistocene
The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...
, the West Indian manatee had a wider range across North America with fossils being found in
Texas
Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...
, and the
Mississippi River
The Mississippi River is the main stem, primary river of the largest drainage basin in the United States. It is the second-longest river in the United States, behind only the Missouri River, Missouri. From its traditional source of Lake Ita ...
and
Ohio River
The Ohio River () is a river in the United States. It is located at the boundary of the Midwestern and Southern United States, flowing in a southwesterly direction from Pittsburgh, Pennsylvania, to its river mouth, mouth on the Mississippi Riv ...
.
An analysis of
mitochondrial DNA
Mitochondrial DNA (mtDNA and mDNA) is the DNA located in the mitochondrion, mitochondria organelles in a eukaryotic cell that converts chemical energy from food into adenosine triphosphate (ATP). Mitochondrial DNA is a small portion of the D ...
patterns indicates there are actually three primary geographic groups of the West Indian manatee: (i) Florida and the
Greater Antilles
The Greater Antilles is a grouping of the larger islands in the Caribbean Sea, including Cuba, Hispaniola, Puerto Rico, and Jamaica, together with Navassa Island and the Cayman Islands. Seven island states share the region of the Greater Antille ...
; (ii) Mexico,
Central America
Central America is a subregion of North America. Its political boundaries are defined as bordering Mexico to the north, Colombia to the southeast, the Caribbean to the east, and the Pacific Ocean to the southwest. Central America is usually ...
and northern South America; and (iii) northeastern South America.
[
The seasonal distribution of the West Indian manatee varies with water temperatures. Temperatures below approximately increase the risk of cold-induced stress or mortality for manatees.] Consequently, Florida manatees seek out warm-water refuges during the winter, concentrated primarily along the Florida peninsula. Many of these refuges are artificial, created by the runoff from nearby power plants. In contrast, the Antillean manatee is less susceptible to cold-induced stress due to the warmer waters across its range.
Florida manatees inhabit the most northern limit of sirenian habitats. There are four recognized subpopulations of the Florida manatee, termed the Northwest, Southwest, Atlantic Coast and St. John's River populations. Large concentrations of Florida manatees are located in the Crystal River and Blue Spring regions in central and north Florida. The Antillean manatee is sparsely distributed throughout the Caribbean and the northwestern Atlantic Ocean, from Mexico
Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...
, east to the Greater Antilles
The Greater Antilles is a grouping of the larger islands in the Caribbean Sea, including Cuba, Hispaniola, Puerto Rico, and Jamaica, together with Navassa Island and the Cayman Islands. Seven island states share the region of the Greater Antille ...
, and south to Brazil
Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...
. Populations can also be found in The Bahamas
The Bahamas, officially the Commonwealth of The Bahamas, is an Archipelagic state, archipelagic and island country within the Lucayan Archipelago of the Atlantic Ocean. It contains 97 per cent of the archipelago's land area and 88 per cent of ...
, French Guiana
French Guiana, or Guyane in French, is an Overseas departments and regions of France, overseas department and region of France located on the northern coast of South America in the Guianas and the West Indies. Bordered by Suriname to the west ...
, Suriname
Suriname, officially the Republic of Suriname, is a country in northern South America, also considered as part of the Caribbean and the West Indies. It is a developing country with a Human Development Index, high level of human development; i ...
, Guyana
Guyana, officially the Co-operative Republic of Guyana, is a country on the northern coast of South America, part of the historic British West Indies. entry "Guyana" Georgetown, Guyana, Georgetown is the capital of Guyana and is also the co ...
, Trinidad
Trinidad is the larger, more populous island of the Republic of Trinidad and Tobago, the country. The island lies off the northeastern coast of Venezuela and sits on the continental shelf of South America. It is the southernmost island in ...
, Venezuela
Venezuela, officially the Bolivarian Republic of Venezuela, is a country on the northern coast of South America, consisting of a continental landmass and many Federal Dependencies of Venezuela, islands and islets in the Caribbean Sea. It com ...
, Colombia
Colombia, officially the Republic of Colombia, is a country primarily located in South America with Insular region of Colombia, insular regions in North America. The Colombian mainland is bordered by the Caribbean Sea to the north, Venezuel ...
, Panama
Panama, officially the Republic of Panama, is a country in Latin America at the southern end of Central America, bordering South America. It is bordered by Costa Rica to the west, Colombia to the southeast, the Caribbean Sea to the north, and ...
, Costa Rica
Costa Rica, officially the Republic of Costa Rica, is a country in Central America. It borders Nicaragua to the north, the Caribbean Sea to the northeast, Panama to the southeast, and the Pacific Ocean to the southwest, as well as Maritime bo ...
, Curaçao
Curaçao, officially the Country of Curaçao, is a constituent island country within the Kingdom of the Netherlands, located in the southern Caribbean Sea (specifically the Dutch Caribbean region), about north of Venezuela.
Curaçao includ ...
, Nicaragua
Nicaragua, officially the Republic of Nicaragua, is the geographically largest Sovereign state, country in Central America, comprising . With a population of 7,142,529 as of 2024, it is the third-most populous country in Central America aft ...
, Honduras
Honduras, officially the Republic of Honduras, is a country in Central America. It is bordered to the west by Guatemala, to the southwest by El Salvador, to the southeast by Nicaragua, to the south by the Pacific Ocean at the Gulf of Fonseca, ...
, Guatemala
Guatemala, officially the Republic of Guatemala, is a country in Central America. It is bordered to the north and west by Mexico, to the northeast by Belize, to the east by Honduras, and to the southeast by El Salvador. It is hydrologically b ...
, Belize
Belize is a country on the north-eastern coast of Central America. It is bordered by Mexico to the north, the Caribbean Sea to the east, and Guatemala to the west and south. It also shares a maritime boundary with Honduras to the southeast. P ...
, Cuba
Cuba, officially the Republic of Cuba, is an island country, comprising the island of Cuba (largest island), Isla de la Juventud, and List of islands of Cuba, 4,195 islands, islets and cays surrounding the main island. It is located where the ...
, the Dominican Republic
The Dominican Republic is a country located on the island of Hispaniola in the Greater Antilles of the Caribbean Sea in the Atlantic Ocean, North Atlantic Ocean. It shares a Maritime boundary, maritime border with Puerto Rico to the east and ...
, Jamaica
Jamaica is an island country in the Caribbean Sea and the West Indies. At , it is the third-largest island—after Cuba and Hispaniola—of the Greater Antilles and the Caribbean. Jamaica lies about south of Cuba, west of Hispaniola (the is ...
and Puerto Rico
; abbreviated PR), officially the Commonwealth of Puerto Rico, is a Government of Puerto Rico, self-governing Caribbean Geography of Puerto Rico, archipelago and island organized as an Territories of the United States, unincorporated territo ...
. It is possibly extirpated
Local extinction, also extirpation, is the termination of a species (or other taxon) in a chosen geographic area of study, though it still exists elsewhere. Local extinctions are contrasted with global extinctions.
Local extinctions mark a chan ...
from the Turks and Caicos Islands
The Turks and Caicos Islands (abbreviated TCI; and ) are a British Overseas Territory consisting of the larger Caicos Islands and smaller Turks Islands, two groups of tropical islands in the Lucayan Archipelago of the Atlantic Ocean and no ...
, and definitively so from all the Lesser Antilles
The Lesser Antilles is a group of islands in the Caribbean Sea, forming part of the West Indies in Caribbean, Caribbean region of the Americas. They are distinguished from the larger islands of the Greater Antilles to the west. They form an arc w ...
except Trinidad and Curaçao. Its presence in Haiti
Haiti, officially the Republic of Haiti, is a country on the island of Hispaniola in the Caribbean Sea, east of Cuba and Jamaica, and south of the Bahamas. It occupies the western three-eighths of the island, which it shares with the Dominican ...
is uncertain. A reintroduction was planned to take place in Guadeloupe
Guadeloupe is an Overseas departments and regions of France, overseas department and region of France in the Caribbean. It consists of six inhabited islands—Basse-Terre Island, Basse-Terre, Grande-Terre, Guadeloupe, Grande-Terre, Marie-Galant ...
, but was terminated early due to political issues.
Behavior and diet
Behavior
Because manatees evolved in habitats without natural predators, they lack predator avoidance behavior. The large size and low metabolic rates of manatees lends to their capacity for long and deep dives, as well as their relative lack of speed. Manatees are frequently solitary creatures, but they do aggregate at warm-water habitats during the winter and during the formation of breeding herds. In spite of their docile demeanor, due to their large size the West Indian manatee has nearly no natural predators in its native environment. American alligators and American crocodile
The American crocodile (''Crocodylus acutus'') is a species of crocodilian found in the Neotropics. It is the most widespread of the four Extant taxon, extant species of crocodiles from the Americas, with populations present from South Florida, ...
s have been suspected to on occasion take a manatee. A dying manatee was discovered in Puerto Rico, wounded by a large shark bite thought to be inflicted by either a tiger shark
The tiger shark (''Galeocerdo cuvier'') is a species of ground shark, and the only extant member of the genus '' Galeocerdo'' and family Galeocerdonidae. It is a large apex predator, with females capable of attaining a length of over . Popula ...
or bull shark
The bull shark (''Carcharhinus leucas''), also known as the Zambezi shark (informally zambi) in Africa and Lake Nicaragua shark in Nicaragua, is a species of requiem shark commonly found worldwide in warm, shallow waters along coasts and in riv ...
. It is projected that large sharks may threaten manatees occasionally but rarely enter the manatee's brackish habitats, whereas marine mammals in more direct coastal oceanic waters are well known to be highly vulnerable to sharks and orca
The orca (''Orcinus orca''), or killer whale, is a toothed whale and the largest member of the oceanic dolphin family. The only extant species in the genus '' Orcinus'', it is recognizable by its black-and-white-patterned body. A cosmopol ...
s.
Communication
Manatees have been shown to form large mating herds when males come across estrous females, indicating that males may be able to sense estrogen
Estrogen (also spelled oestrogen in British English; see spelling differences) is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three ...
or other chemical indicators. Manatees can communicate information to each other through their vocalization patterns. Sex and age-related differences are apparent in the vocalization structure of common squeaks and screeches in adult males, adult females, and juveniles. This may be an indication of vocal individuality among manatees. An increase in manatee vocalization after a vocal playback stimulus shows that they may be able to recognize another manatee's individual voice. This behavior in manatees is found mostly between mother and calf interactions. However, vocalization can still be commonly found in a variety of social interactions within groups of manatees, which is similar to other aquatic mammals. When communicating in noisy environments, manatees that are in groups experience the same Lombard effect as humans do; where they will involuntary increase their vocal effort when communicating in loud environments. Based on acoustic and anatomical evidence, mammalian vocal folds
In humans, the vocal cords, also known as vocal folds, are folds of throat tissues that are key in creating sounds through Speech, vocalization. The length of the vocal cords affects the pitch of voice, similar to a violin string. Open when brea ...
are assumed to be the mechanism for sound production in manatees. Manatees also eat other manatees' feces; it is assumed that they do this to gather information about reproductive status or dominance, indicating the important role chemoreception plays in the social and reproductive behavior of manatees.
Diet
Manatees are obligate herbivores that feed on over 60 species of aquatic plants in both fresh and salt water. Seagrass
Seagrasses are the only flowering plants which grow in marine (ocean), marine environments. There are about 60 species of fully marine seagrasses which belong to four Family (biology), families (Posidoniaceae, Zosteraceae, Hydrocharitaceae and ...
is a staple of the manatee diet, particularly in coastal areas. In addition, when the tide is high enough, they will also feed on grasses, roots and leaves (including those of mangrove
A mangrove is a shrub or tree that grows mainly in coastal saline water, saline or brackish water. Mangroves grow in an equatorial climate, typically along coastlines and tidal rivers. They have particular adaptations to take in extra oxygen a ...
s), as well as algae. Manatees typically graze for five or more hours per day, consuming anywhere from 4% to 10% of their body weight in wet vegetation per day, though the exact amount depends on their body size and activity level. Because manatees feed on abrasive plants, their molars
The molars or molar teeth are large, flat tooth, teeth at the back of the mouth. They are more developed in mammal, mammals. They are used primarily to comminution, grind food during mastication, chewing. The name ''molar'' derives from Latin, '' ...
are often worn down and are replaced many times throughout their lives, thus earning the nickname "marching molars." The molar teeth are similar in shape, but of varying sizes. Manatees do not have incisors; these have been replaced by horny gingival plates. Some individuals may also inadvertently eat invertebrates (such as small aquatic insects and crustaceans) and will eat fish both in captivity and in the wild.
Manatees are nonruminants with an enlarged hindgut
The hindgut (or epigaster) is the posterior ( caudal) part of the alimentary canal. In mammals, it includes the distal one third of the transverse colon and the splenic flexure, the descending colon, sigmoid colon and up to the ano-rectal junct ...
. Unlike other hindgut fermenters, such as the horse, manatees efficiently extract nutrients, particularly cellulose, from the aquatic plants in their diet. Manatees have a large gastrointestinal tract with contents measuring about 23% of its total body mass. In addition, the passage rate of food is very long (about seven days). This slow process increases the digestibility of their diet. It is suggested that chronic fermentation may also provide additional heat and is correlated with their low metabolic rate.
Vibrissae
Manatees have sensitive tactile hairs that cover their bodies and faces called whiskers
Whiskers, also known as vibrissae (; vibrissa; ) are a type of stiff, functional hair used by most therian mammals to sense their environment. These hairs are finely specialised for this purpose, whereas other types of hair are coarser as ta ...
or ''vibrissae''. Each individual hair is a vibrissal apparatus called a follicle-sinus complex. Vibrissae are blood filled sinuses bound by a dense connective tissue capsule with sensitive nerve endings that provides haptic feedback to the manatee.
Usually vibrissae are found on the facial regions of terrestrial and non-sirenian aquatic animals and are called whiskers
Whiskers, also known as vibrissae (; vibrissa; ) are a type of stiff, functional hair used by most therian mammals to sense their environment. These hairs are finely specialised for this purpose, whereas other types of hair are coarser as ta ...
. Manatees, however, have vibrissae all over their bodies. The vibrissae located in their facial region are roughly 30 times denser than the vibrissae on the rest of their body. Their mouth consists of very mobile prehensile
Prehensility is the quality of an appendage or organ that has adapted for grasping or holding. The word is derived from the Latin term ''prehendere'', meaning "to grasp". The ability to grasp is likely derived from a number of different origin ...
lips which are used for grasping food and objects. The vibrissae on these lips are turned outward during grasping and are used in locating vegetation. Their oral disks also contain vibrissae which have been classified as bristle-like hairs that are used in nongrasping investigation of objects and food.[
Manatee vibrissae are so sensitive that they are able to perform active touch discrimination of textures. Manatees also use their vibrissae to navigate the turbid waterways of their environment. Research has indicated that they are able to use these vibrissae to detect hydrodynamic stimuli in the same way that fish use their ]lateral line
The lateral line, also called the lateral line organ (LLO), is a system of sensory organs found in fish, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory ability is achieved via modified epithelia ...
system.
Reproduction
Male manatees reach sexual maturity at 3–4 years of age, while females reach sexual maturity at 3–5 years of age. Manatees appear capable of breeding throughout their entire adult life, although most females first breed successfully at ages 7–9. Breeding occurs in ephemeral mating herds, where several males aggregate around an estrous female and compete for access to her. These mating herds can last up to 2 to 4 weeks. The estrous cycles of female manatees typically are approximately one month long. Females in captivity have been observed to skip cycles.[ Larger males, presumably older, have been observed to dominate mating herds and are likely responsible for most successful copulation events.] However, between males and females there is a little sexual dimorphism where females are typically slightly larger than males.
The reproductive anatomy of males consists of internal testes within the abdominal cavity, which are located posterior to the kidneys. In the Florida manatee, males experience seasonal changes in their spermatogenesis. They are active during the warm breeding season; during this time all stages of spermatogenesis can be seen. However, during the cold non-breeding season, they are inactive, and spermatogenesis is inhibited.
Recently there has been a study that shows support that males use chemosensation for the anal glands to locate females in estrous.
The reproductive anatomy of females is most like that of elephants. Female manatees resemble elephants in their zonary placenta, bicornuate uterus, and corpora albicantia. The female manatees' ovary gross morphology consists of an oval disk shape with a flat surface of the cortex. And since they are polyovular the ovulation scar is often challenging to identify.
The gestation
Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pregn ...
period in manatees lasts for 12–14 months, after which they give birth to one calf at a time or, rarely, twins. When twins are born, they are fraternal twins and are dizygotic. When a calf is born, it usually weighs and is long. Manatees do not form permanent pair bond
In biology, a pair bond is the strong affinity that develops in some species between a mating pair, often leading to the production and rearing of young and potentially a lifelong bond. Pair-bonding is a term coined in the 1940s that is frequently ...
s, and the male contributes no parental care to the calf, which remains with the mother for up to two years prior to weaning. Female manatees have two axillary mammary glands located under their flippers. The lactation period for mothers and their calves last typically for one to two years. Prior to weaning, there is an increase in the hormone progesterone in the mother.
During this two-year period with their mother, calves learn how to locate warm water sources for winter and about migration routes for the summer seasons. A single female can reproduce once every 2–3 years, which is referred to as the calving interval. Wild manatees have been documented producing offspring into their late 30s, and a female captive manatee has given birth in her 40s.
Captive breeding programs are not being conducted for the Florida manatee due to conservation concerns that are being addressed in their natural environments. Until these concerns are rectified, a captive breeding program will not be beneficial for this species.
Threats and conservation
The West Indian manatee has been included on the U.S. Endangered Species List since the 1970s. Late in 2023, the International Union for Conservation of Nature
The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the stat ...
(IUCN) assessed the West Indian manatee and the Florida subspecies as vulnerable, and the Antillean subspecies as endangered. The full species and both subspecies qualified for their respective classifications due to a combination of a low number of mature individuals, and a significant projected decline in total population numbers over the next two generations (about 20 years per generation in manatees). Similarly, NatureServe
NatureServe, Inc. is a non-profit organization based in Arlington County, Virginia, United States, US, that provides proprietary wildlife conservation-related data, tools, and services to private and government clients, partner organizations, and ...
considers both the Florida subspecies and the species as a whole as "Imperiled".
The Florida and Antillean subspecies face different threats, though some overlap. The largest causes of Florida manatee deaths can be attributed to collisions with watercraft, the loss of warm-water habitat, high perinatal mortality, entanglements and ingestion of debris, pollution, habitat loss, and harmful algae blooms (HABs), such as red tide
A harmful algal bloom (HAB), or excessive algae growth, sometimes called a red tide in marine environments, is an algal bloom that causes negative impacts to other organisms by production of natural algae-produced toxins, water deoxygenation, ...
. Antillean manatees face severe habitat fragmentation
Habitat fragmentation describes the emergence of discontinuities (fragmentation) in an organism's preferred environment (habitat), causing population fragmentation and ecosystem decay. Causes of habitat fragmentation include geological proces ...
, as well as continued pressure from illegal hunting. In some countries, like Belize, collisions with watercraft are on the rise as tourism grows.
The 2017 decision to reclassify the West Indian manatee from endangered to threatened under the Endangered Species Act cited increases in the populations of both subspecies. The decision was not without controversy, however: According to Save the Manatee Club, the U.S. Fish and Wildlife Service failed to adequately consider data from 2010 to 2016, during which time manatees suffered from unprecedented mortality events linked to habitat pollution, dependence on artificial warm-water sources, and record deaths from watercraft strikes. The official notice of the reclassification made clear that, even with the downlisting, all federal protections for the West Indian manatee under the Endangered Species Act would remain in place. The West Indian manatee is also protected by the Florida Manatee Sanctuary Act of 1978 and the U.S. Marine Mammal Protection Act of 1972
The Marine Mammal Protection Act (MMPA) was the first act of Congress, act of the United States Congress to call specifically for an ecosystem approach to wildlife management.
Authority
MMPA was signed into law on October 21, 1972, by Preside ...
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''T. m. latirostris'' (Florida manatee)
A 1997 population viability analysis of the Florida manatee projected a 44% chance of extinction within the next 1,000 years without improvements in habitat conditions and new protective regulations. Since then, prospects for the subspecies have improved. In 2016, the U.S. Geological Survey
The United States Geological Survey (USGS), founded as the Geological Survey, is an agency of the U.S. Department of the Interior whose work spans the disciplines of biology, geography, geology, and hydrology. The agency was founded on March ...
collaborated with the Florida Fish and Wildlife Service to re-evaluate the status of the Florida manatee under the Core Biological Model, which is used to estimate population viability. This assessment analyzed total population on the east and west coasts of Florida and estimated that the likelihood of either population falling under 500 adults within 100 years was about 0.42%. The projected improvement of population numbers and stability is contingent on continued intervention and monitoring efforts.
Collision with watercraft
Over 20% of manatee mortalities per year are a result of watercraft collisions. Between 1985 and 2017, 53% of adult-manatee mortalities were the result of boat strikes. 96% of adult Florida manatee carcasses have scars from a boat collision with some individuals showing signs of 10 or more boat strikes. Manatees can hear boats, but they oftentimes do not have enough time to get out of the way of a fast approaching boat. A boat going at a slower speed gives the manatee more time to react and move out of the way. Manatees respond to approaching vessels by orienting towards deeper waters and increasing their speed, but they are nevertheless frequently struck as they don't have the ability to swim very fast and, in shallow habitat, they oftentimes don't have anywhere to go to get out of the way. Over half of all watercraft deaths are caused by the impact trauma from the hull of a fast-speeding boat, whereas the remaining percentage is caused by the boat propeller. Aerial surveys of Florida manatee and boat distribution have been conducted to map the areas in which collisions are most likely to occur, accounting for environmental and seasonal factors. Watercraft can frequently avoid hitting manatees simply by reducing speed, allowing time for the manatee to escape out of range. Despite improvements in modeling and changes to local regulations, manatee mortalities from watercraft collisions continue to rise, with an all-time high of 137 recorded deaths in 2019.
Loss of warm-water habitat
Projected long-term loss of warm-water habitats presents a significant risk to manatees, which are unable to tolerate temperatures lower than for prolonged periods of time. Florida manatees frequently congregate around natural warm-water springs, as well as the warm discharge given off by power plants throughout the winter months. However, as older plants are replaced with more energy-efficient structures, manatees could become at risk of cold-induced death due to reduced availability of warm-water refuges. Manatees exhibit high site fidelity and can recall previous refuge sites to which they frequently return in successive winters. Some conservationists fear that manatees may become overly reliant on warm-water locations generated by power plants that may shut down soon. Natural warm-water springs face problems from over-pumping of groundwater for human consumption, reduced spring flow, and nutrient pollution. In addition, some springs that were historically accessible to manatees are blocked off by dams or other structures. As Florida moves towards net zero by 2050, power companies will likely phase out these warm water discharges. Florida Climate Institute's Laying the Groundwork for 'Getting to Neutral' in the State of Florida project sets a foundation for a net-zero action planning effort in Florida by 2050. In areas where manatees lack access to power plants or natural warm springs, they instead seek out natural deep water zones that passively remain above tolerable temperatures.
Harmful algae blooms
Harmful algae blooms are an additional threat to manatees. Red tide
A harmful algal bloom (HAB), or excessive algae growth, sometimes called a red tide in marine environments, is an algal bloom that causes negative impacts to other organisms by production of natural algae-produced toxins, water deoxygenation, ...
is a common name for algal blooms, deriving its distinctive color from pigmentation molecules in the algae. The blooms produce brevetoxins which are potentially fatal to marine life. Most manatee deaths from red tide occur when manatees inhale the toxins, or ingest the toxins when consuming seagrass, their primary food source. During a 1996 epizootic more than 150 manatees died from red tide exposure. Although manatees can survive exposure to red tide if rescued and rehabilitated in time, researchers fear that there might be long-term effects from sub-lethal red-tide exposure, which can affect the manatee's immune system through reduced lymphocyte proliferation response. In addition to red tide, blue/green and brown algae blooms triggered by excessive nutrient pollution from fertilizer, runoff, and leaking septic tanks can cloud the water. This results in seagrasses dying off since seagrasses and aquatic plants need light to photosynthesize. Manatees in turn may not be able to find sufficient food sources, which can lead to starvation. Manatees have experienced several Unusual Mortality Events (UMEs) over the years, which are usually related to either cold-stress syndrome, or brevetoxicosis from red tide. A current UME is ongoing along the Atlantic coast of Florida and is most likely related to a shortage in food sources.
Entanglement, entrapment and ingestion of debris
Manatees easily can get entangled in monofilament fishing line, crab traps, and other debris, which can lead to the loss of flippers and severe body wraps. In addition, they may also ingest a variety of debris, such as plastics, cloth, fishing gear, and other items. Manatees can also get crushed by flood control structures and locks and may get entrapped behind weirs or other structures, especially after heavy rainfall. Some manatees have gotten trapped in culverts and pipes and needed intervention.
''T. m. manatus'' (Antillean manatee)
There is relatively little data on the Antillean manatee compared to its Florida counterpart. Phylogenetic studies on the Antillean manatee have revealed low genetic diversity among its populations, likely due to limitations on dispersal. Captive breeding, as well as the rehabilitation of manatee calves discovered without their mothers nearby, can supplement local conservation strategies, but populations are nevertheless at risk of inbreeding depression and local extinction.
Whereas the population trends of the Florida manatee are relatively well monitored, population data for the Antillean manatee is sparse due to its patchy distribution, as well as the relative turbidity
Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of both water clarity and wa ...
and low levels of light in its habitat which can mitigate the effectiveness of aerial or sonar-based surveys, often resulting in inaccurate or erroneous measurements. A 2016 study on the Antillean manatee population of Brazil found a potential range for current population size between 485 and 2,221 individuals. The U.S. Fish and Wildlife Service estimated in 2017 that as many as 6,782 individuals might exist in the Antillean subspecies, but these results rely in large part on personal anecdotes and may overestimate the true population number. A 2012 study of the Antillean population documented significant human-related causes of mortality, and projected that if the share of human-caused manatee deaths per year rose to 5% or more, the population would face a severe decline and eventual extinction.
References
External links
*ARKive �
images and movies of the West Indian manatee (''Trichechus manatus'')
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Manatees Lived in Texas During the Last Ice Age
on: SciTechAlert, October 4, 2020, Source: University of Texas at Austin.
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Manatees
EDGE species
ESA threatened species
Mammals of Brazil
Mammals of Colombia
Mammals of French Guiana
Mammals of Guyana
Mammals of the Dominican Republic
Mammals of Haiti
Mammals of Puerto Rico
Mammals of the Bahamas
Mammals of the Caribbean
Mammals of the United States
Mammals of Trinidad and Tobago
Mammals described in 1758
Taxa named by Carl Linnaeus
Symbols of Florida
Natural history of Florida