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==Description==
==Description==
The average West Indian manatee is about {{convert|2.7|-|3.5|m|ft|abbr=on}} long and weighs {{convert|200|-|600|kg|lb| abbr=on}}, with females generally larger than males.<ref>[http://141.213.176.11/site/accounts/information/Trichechus_manatus.html ''Trichechus manatus''] {{webarchive|url=https://web.archive.org/web/20110904034008/http://141.213.176.11/site/accounts/information/Trichechus_manatus.html |date=2011-09-04 }}, Animal Diversity Web</ref> 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.<ref>{{cite journal | last1 = Rommel | first1 = S.A. | last2 = Caplan | first2 = D. H. | year = 2003 | title = Vascular adaptations for heat conservation in the tail of Florida manatees (''Trichechus manatus latirostris'') | journal = Journal of Anatomy | volume = 202 | issue = 4 | pages = 343–353 | doi = 10.1046/j.1469-7580.2003.00170.x | pmid = 12739612 | pmc=1571090}}</ref> The largest individual on record weighed {{convert|1655|kg|lb|abbr=on}} and measured {{convert|4.6|m|ft|abbr=on}} long.<ref>Wood, G.L. (1983). ''The Guinness Book of Animal Facts and Feats.'' 3rd revised edition. Sterling Pub Co Inc., {{ISBN|978-0851122359}}</ref><ref>[http://www.seaworld.org/Animal-info/animal-bytes/animalia/eumetazoa/coelomates/deuterostomes/chordata/craniata/mammalia/sirenia/manatees.htm Manatees] {{webarchive|url=https://web.archive.org/web/20120118065736/http://www.seaworld.org/animal-info/animal-bytes/animalia/eumetazoa/coelomates/deuterostomes/chordata/craniata/mammalia/sirenia/manatees.htm |date=2012-01-18 }}, Busch Gardens</ref>
The average West Indian manatee is about {{convert|2.7|-|3.5|m|ft|abbr=on}} long and weighs {{convert|200|-|600|kg|lb|abbr=on}}, with females generally larger than males.<ref>[http://141.213.176.11/site/accounts/information/Trichechus_manatus.html ''Trichechus manatus''] {{webarchive|url=https://web.archive.org/web/20110904034008/http://141.213.176.11/site/accounts/information/Trichechus_manatus.html|date=2011-09-04}}, Animal Diversity Web</ref> The largest individual on record weighed {{convert|1655|kg|lb|abbr=on}} and measured {{convert|4.6|m|ft|abbr=on}} long.<ref>Wood, G.L. (1983). ''The Guinness Book of Animal Facts and Feats.'' 3rd revised edition. Sterling Pub Co Inc., {{ISBN|978-0851122359}}</ref><ref>[http://www.seaworld.org/Animal-info/animal-bytes/animalia/eumetazoa/coelomates/deuterostomes/chordata/craniata/mammalia/sirenia/manatees.htm Manatees] {{webarchive|url=https://web.archive.org/web/20120118065736/http://www.seaworld.org/animal-info/animal-bytes/animalia/eumetazoa/coelomates/deuterostomes/chordata/craniata/mammalia/sirenia/manatees.htm|date=2012-01-18}}, Busch Gardens</ref> Manatees are estimated to live 50 years or more in the wild<ref name=":22">{{Cite web|url=https://www.fws.gov/verobeach/ListedSpeciesMSRP.html|title=South Florida Multi-Species Recovery Plan|last=|first=|date=|website=|url-status=live|archive-url=|archive-date=|access-date=}}</ref>, and one captive Florida manatee, [[Snooty]], lived for 69 years.<ref>{{Cite web|url=http://www.foxnews.com/us/2017/07/23/snooty-worlds-oldest-known-manatee-dies-one-day-after-celebrating-birthday.html|title=Snooty, world's oldest known manatee, dies one day after celebrating birthday|date=2017-07-23|website=Fox News|language=en-US|url-status=live|archiveurl=https://web.archive.org/web/20170723193131/http://www.foxnews.com/us/2017/07/23/snooty-worlds-oldest-known-manatee-dies-one-day-after-celebrating-birthday.html|archivedate=2017-07-23|access-date=2017-07-23}}</ref>
[[File:West Indian Manatee Skull.jpg|left|thumb|Skull of a West Indian manatee on display at [[The Museum of Osteology]], [[Oklahoma City, Oklahoma]]]]
[[File:West_Indian_Manatee_Skull.jpg|link=https://en.wikipedia.org/wiki/File:West_Indian_Manatee_Skull.jpg|left|thumb|Skull of a West Indian manatee on display at [[The Museum of Osteology]], [[Oklahoma City, Oklahoma]]]]
⚫
Since manatees are [[Mammal|mammals]], they breathe air, have warm blood, have hair, and give birth to live young. Like the other [[Sirenian|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 [[Barnacle|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.<ref name="“reep2006”2">Reep, R. L. & Bonde, R. K. (2006). ''The Florida manatee: Biology and conservation''. Gainesville: The University Press of Florida.</ref>


⚫
The West Indian manatee has a prehensile snout, like their relative the [[elephant]], for grabbing vegetation and bringing it into their mouths. Manatees have six to eight [[Molar (tooth)|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 system|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 [[Thoracic diaphragm|diaphragm]] that is spit in half to form two hemidiaphragms. Each hemidiaphragm is capable of independent muscular contractions.<ref name="“reep2006”2" />
⚫
Since manatees are [[mammal]]s, they breathe air, have warm blood, have hair, and give birth to live young. Like the other [[sirenian]]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]] 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 [[barnacle]]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. Nails are absent in the [[Amazonian manatee]]. <ref name = “reep2006”>Reep, R. L. & Bonde, R. K. (2006). ''The Florida manatee: Biology and conservation''. Gainesville: The University Press of Florida.</ref>

⚫
The West Indian manatee has a prehensile snout, like their relative the [[elephant]], for grabbing vegetation and bringing it into their mouths. Manatees have six to eight [[molar (tooth)|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 system|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 [[Thoracic diaphragm|diaphragm]] that is spit in half to form two hemidiaphragms. Each hemidiaphragm is capable of independent muscular contractions. <ref name = “reep2006”/>


==Distribution and habitat==
==Distribution and habitat==
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 [[river]]s and [[Estuary|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 [[blubber|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]].<ref>[http://www.buzzardsbay.org/buzzards-bay-manatees.htm Manatees] {{webarchive|url=https://web.archive.org/web/20120508040544/http://www.buzzardsbay.org/buzzards-bay-manatees.htm |date=2012-05-08 }}, Buzzards Bay National Estuary Program</ref> A manatee was spotted in the Wolf River (near where it enters the Mississippi) in Memphis, Tennessee in 2006.<ref>{{cite news|url=http://www.nbcnews.com/id/16160935/ns/us_news-environment/t/manatee-found-dead-tenn-lake|title=Manatee found dead in Tenn. lake|agency=Associated Press|date=11 December 2006|accessdate=24 June 2017|url-status=live|archiveurl=https://web.archive.org/web/20160924124042/http://www.nbcnews.com/id/16160935/ns/us_news-environment/t/manatee-found-dead-tenn-lake/|archivedate=24 September 2016}}</ref>
The West Indian manatee inhabits mostly shallow coastal areas, including [[River|rivers]] and [[Estuary|estuaries]]. Manatees can withstand large changes in [[salinity]] and have been found in highly brackish and saline waters.<ref name=":24">{{Cite web|url=https://www.fws.gov/verobeach/ListedSpeciesMSRP.html|title=South Florida Multi-Species Recovery Plan|last=|first=|date=|website=|url-status=live|archive-url=|archive-date=|access-date=}}</ref> Manatees' extremely low metabolic rate and lack of a thick layer of [[Blubber|insulating body fat]] limits them to locations with warm waters, including tropical regions. Although most commonly found along the Florida coast, the West Indian manatee has been spotted as far north as [[Dennis, Massachusetts]], and as far west as Texas.<ref name=":02">[http://www.buzzardsbay.org/buzzards-bay-manatees.htm Manatees] {{webarchive|url=https://web.archive.org/web/20120508040544/http://www.buzzardsbay.org/buzzards-bay-manatees.htm|date=2012-05-08}}, Buzzards Bay National Estuary Program</ref> A manatee was spotted in the [[Wolf River (Tennessee)|Wolf River]] (near where it enters the Mississippi) in [[Memphis, Tennessee]] in 2006.<ref>{{cite news|url=http://www.nbcnews.com/id/16160935/ns/us_news-environment/t/manatee-found-dead-tenn-lake|title=Manatee found dead in Tenn. lake|date=11 December 2006|accessdate=24 June 2017|url-status=live|archiveurl=https://web.archive.org/web/20160924124042/http://www.nbcnews.com/id/16160935/ns/us_news-environment/t/manatee-found-dead-tenn-lake/|archivedate=24 September 2016|agency=Associated Press}}</ref> An analysis of [[mitochondrial DNA]] patterns indicates there are actually three primary geographic groups of the West Indian manatee: (1) Florida and the [[Greater Antilles]]; (2) Mexico, [[Central America]] and northern South America; and (3) northeastern South America.''<ref>{{cite journal|last1=Garcia-Rodriguez|first1=A. I.|last2=Bowen|first2=B. W.|last3=Domning|first3=D|last4=Mignucci-Giannoni|first4=A|last5=Marmontel|first5=M|last6=Montoya-Ospina|first6=A|last7=Morales-Vela|first7=B|last8=Rudin|first8=M|last9=Bonde|first9=R. K.|last10=McGuire|first10=P. M.|year=1998|title=Phylogeography of the West Indian manatee (''Trichechusmanatus''): How many populations and how many taxa?|journal=Molecular Ecology|volume=7|issue=9|pages=1137–1149|doi=10.1046/j.1365-294x.1998.00430.x|pmid=9734072}}</ref><ref>{{cite journal|last1=Vianna|first1=J. A.|last2=Bonde|first2=R. K.|last3=Caballero|first3=S|last4=Giraldo|first4=J. P.|last5=Lima|first5=R. P.|last6=Clark|first6=A|last7=Marmontel|first7=M|last8=Morales-Vela|first8=B|last9=De Souza|first9=M. J.|last10=Parr|first10=L|last11=Rodríguez-Lopez|first11=M. A.|year=2006|title=Phylogeography, phylogeny and hybridization in trichechid sirenians: implications for manatee conservation|journal=Molecular Ecology|volume=15|issue=2|pages=433–47|doi=10.1111/j.1365-294X.2005.02771.x|pmid=16448411|last12=Mignucci-Giannoni|first12=A. A.|last13=Powell|first13=J. A.|last14=Santos|first14=F. R.}}</ref>''
⚫
[[File:Manatee Florida.jpg|thumb|left|Manatee from [[Crystal River, Florida]]]]

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 [[NGO]]s 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.<ref>{{Cite web |url=http://www.foxnews.com/us/2017/07/23/snooty-worlds-oldest-known-manatee-dies-one-day-after-celebrating-birthday.html |title=Snooty, world's oldest known manatee, dies one day after celebrating birthday |date=2017-07-23 |website=Fox News |language=en-US |access-date=2017-07-23 |url-status=live |archiveurl=https://web.archive.org/web/20170723193131/http://www.foxnews.com/us/2017/07/23/snooty-worlds-oldest-known-manatee-dies-one-day-after-celebrating-birthday.html |archivedate=2017-07-23 }}</ref>

Large concentrations of Florida manatees are located in the Crystal River<ref>{{Cite news|url=https://www.birdsunderwater.com/about-the-manatees/|title=About the Manatees {{!}} Crystal River, Florida {{!}} Bird's Underwater|work=Birds Underwater|access-date=2017-10-06|language=en-US|url-status=live|archiveurl=https://web.archive.org/web/20171007022147/https://www.birdsunderwater.com/about-the-manatees/|archivedate=2017-10-07}}</ref> and Blue Springs regions in central and north Florida, as well as along the Atlantic Coast, and Florida Gulf Coast.


The seasonal distribution of the West Indian manatee varies with water temperatures. Temperatures below approximately 20°C (68°F) increase the risk of cold-induced stress or mortality for manatees.<ref name=":24" /><ref name="haubold_20072">{{cite report|url=http://myfwc.com/media/415109/Manatee_BSR.pdf|title=Final Biological Status Review of the Florida Manatee (''Trichechus manatus latirostris'')]|author=Haubold, E.|date=April 2006|pages=133|access-date=April 5, 2017|format=PDF|display-authors=etal|series=Assessment 2005–2006|agency=Florida Manatee Biological Review Panel}}</ref> Consequently, Florida manatees seek out warm-water refuges during the winter, concentrated primarily along the Florida peninsula.<ref>{{Cite journal|last=Deutsch|first=Charles J.|last2=Reid|first2=James P.|last3=Bonde|first3=Robert K.|last4=Easton|first4=Dean E.|last5=Kochman|first5=Howard I.|last6=O'Shea|first6=Thomas J.|date=2003|title=Seasonal Movements, Migratory Behavior, and Site Fidelity of West Indian Manatees along the Atlantic Coast of the United States|url=http://www.jstor.org/stable/3830830|journal=Wildlife Monographs|issue=151|pages=1–77|issn=0084-0173}}</ref> Many of these refuges are artificial, created by the runoff from nearby power plants.<ref name=":42">{{Cite journal|last=IUCN|date=2008-06-30|title=Trichechus manatus: Deutsch, C.J., Self-Sullivan, C. & Mignucci-Giannoni, A.: The IUCN Red List of Threatened Species 2008: e.T22103A9356917|url=http://www.iucnredlist.org/details/22103/0|language=en|doi=10.2305/iucn.uk.2008.rlts.t22103a9356917.en}}</ref> In contrast, the Antillean manatee is less susceptible to cold-induced stress due to the warmer waters across its range.
The other subspecies of the West Indian manatee is sometimes referred to as the Antillean manatee (''T. m. manatus''). Antillean manatees are sparsely distributed throughout the Caribbean and the northwestern Atlantic Ocean, from [[Mexico]], east to the [[Greater Antilles]], and south to [[Brazil]]. They are found in [[The Bahamas]], [[French Guiana]], [[Suriname]], [[Guyana]], [[Trinidad]], [[Venezuela]], [[Colombia]], [[Panama]], [[Costa Rica]], [[Nicaragua]], [[Honduras]], [[Guatemala]], [[Belize]], Mexico, [[Cuba]], [[Haiti]], the [[Dominican Republic]], [[Jamaica]], and [[Puerto Rico]]. Historically, Antillean manatees were hunted by local natives and sold to European explorers for food. Today, they are threatened by loss of habitat, poaching, entanglement with fishing gear, and vessel strikes.
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[[File:Manatee_Florida.jpg|link=https://en.wikipedia.org/wiki/File:Manatee_Florida.jpg|left|thumb|Manatee from [[Crystal River, Florida]]]]
Florida manatees inhabit the most northern limit of sirenian habitats. ''T''here are four recognized subpopulations of the Florida manatee, termed the Northwest, Southwest, Atlantic Coast, and [[St. Johns River|St. John's River]] populations.<ref>{{Cite journal|last=Laist|first=David W.|last2=Taylor|first2=Cynthia|last3=Iii|first3=John E. Reynolds|date=2013-03-20|title=Winter Habitat Preferences for Florida Manatees and Vulnerability to Cold|url=https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0058978|journal=PLOS ONE|language=en|volume=8|issue=3|pages=e58978|doi=10.1371/journal.pone.0058978|issn=1932-6203|pmc=PMC3604035|pmid=23527063}}</ref> Large concentrations of Florida manatees are located in the [[Crystal River, Florida|Crystal River]]<ref>{{Cite news|url=https://www.birdsunderwater.com/about-the-manatees/|title=About the Manatees {{!}} Crystal River, Florida {{!}} Bird's Underwater|work=Birds Underwater|access-date=2017-10-06|url-status=live|archiveurl=https://web.archive.org/web/20171007022147/https://www.birdsunderwater.com/about-the-manatees/|archivedate=2017-10-07|language=en-US}}</ref> and [[Blue Spring State Park|Blue Springs]] regions in central and north Florida. The Antillean manatee is sparsely distributed throughout the Caribbean and the northwestern Atlantic Ocean, from [[Mexico]], east to the [[Greater Antilles]], and south to [[Brazil]]. Populations can also be found in [[The Bahamas]], [[French Guiana]], [[Suriname]], [[Guyana]], [[Trinidad]], [[Venezuela]], [[Colombia]], [[Panama]], [[Costa Rica]], [[Nicaragua]], [[Honduras]], [[Guatemala]], [[Belize]], [[Cuba]], [[Haiti]], the [[Dominican Republic]], [[Jamaica]], and [[Puerto Rico]].<ref name="fws_manatee_threatened_20173">{{cite press release|url=https://www.fws.gov/news/ShowNews.cfm?ref=manatee-reclassified-from-endangered-to-threatened-as-habitat-improves-a&_ID=36003|date=March 30, 2017|accessdate=April 4, 2017|title=Manatee Reclassified from Endangered to Threatened as Habitat Improves and Population Expands|website=fws.gov|publisher=[[United States Fish & Wildlife Service|Fish & Wildlife Service]], [[US Department of the Interior]]|url-status=live|archiveurl=https://web.archive.org/web/20170407143427/https://www.fws.gov/news/ShowNews.cfm?ref=manatee-reclassified-from-endangered-to-threatened-as-habitat-improves-a&_ID=36003|archivedate=April 7, 2017}}</ref>


==Behavior and diet==
==Behavior and diet==

Revision as of 14:59, 9 December 2019

West Indian manatee[1]
Adult with calf
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Sirenia
Family: Trichechidae
Genus: Trichechus
Species:
T. manatus
Binomial name
Trichechus manatus
West Indian manatee range

The West Indian manatee (Trichechus manatus) or "sea cow", also known as North 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). It is further divided into two subspecies, the Florida manatee (T. m. latirostris) and the Antillean or Caribbean manatee (T. m. manatus), based on genetic and morphological studies.[4][5] The Florida subspecies is primarily found along the coasts of Florida, but its range extends as far west as Texas and as far north as Massachusetts.[6] The Antillean subspecies has a sparse distribution throughout the Caribbean, ranging as far north as Mexico and as far south as Brazil.[7][8]

Manatees are obligate herbivores, have developed vocal communication abilities, and are covered in highly sensitive vibrissae that are used for feeding and navigation.[9] 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.[10]

The West Indian manatee was listed as endangered under the Endangered Species Act in the 1970's, when there were only several hundred left,[11] and the decades since have witnessed significant efforts by federal, state, private, and nonprofit organizations to protect these species from natural and human-induced threats, particularly collisions with watercraft.[12] On March 30, 2017, the US Secretary of the Interior Ryan Zinke announced the federal reclassification of the West Indian manatee from endangered to threatened, citing a substantial increase in the total population.[11][13]

Description

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.[14] The largest individual on record weighed 1,655 kg (3,649 lb) and measured 4.6 m (15 ft) long.[15][16] Manatees are estimated to live 50 years or more in the wild[17], and one captive Florida manatee, Snooty, lived for 69 years.[18]

Skull of a West Indian manatee on display at The Museum of Osteology, Oklahoma City, Oklahoma

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.[19]

The West Indian manatee has a prehensile snout, like their relative the elephant, for grabbing vegetation and bringing 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.[19]

Distribution and habitat

The West Indian manatee inhabits mostly shallow coastal areas, including rivers and estuaries. Manatees can withstand large changes in salinity and have been found in highly brackish and saline waters.[20] 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. Although most commonly found along the Florida coast, the West Indian manatee has been spotted as far north as Dennis, Massachusetts, and as far west as Texas.[21] A manatee was spotted in the Wolf River (near where it enters the Mississippi) in Memphis, Tennessee in 2006.[22] An analysis of mitochondrial DNA patterns indicates there are actually three primary geographic groups of the West Indian manatee: (1) Florida and the Greater Antilles; (2) Mexico, Central America and northern South America; and (3) northeastern South America.[23][24]

The seasonal distribution of the West Indian manatee varies with water temperatures. Temperatures below approximately 20°C (68°F) increase the risk of cold-induced stress or mortality for manatees.[20][25] Consequently, Florida manatees seek out warm-water refuges during the winter, concentrated primarily along the Florida peninsula.[26] Many of these refuges are artificial, created by the runoff from nearby power plants.[27] In contrast, the Antillean manatee is less susceptible to cold-induced stress due to the warmer waters across its range.

Manatee from Crystal River, Florida

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.[28] Large concentrations of Florida manatees are located in the Crystal River[29] and Blue Springs regions in central and north Florida. The Antillean manatee is sparsely distributed throughout the Caribbean and the northwestern Atlantic Ocean, from Mexico, east to the Greater Antilles, and south to Brazil. Populations can also be found in The Bahamas, French Guiana, Suriname, Guyana, Trinidad, Venezuela, Colombia, Panama, Costa Rica, Nicaragua, Honduras, Guatemala, Belize, Cuba, Haiti, the Dominican Republic, Jamaica, and Puerto Rico.[30]

Behavior and diet

Basking at Haulover Canal, Merritt Island National Wildlife Refuge, Florida

Behavior

The West Indian manatee is surprisingly agile in water, and individuals have been seen doing rolls, somersaults, and even swimming upside-down. Manatees are not territorial and do not have complex predator avoidance behavior, as they have evolved in areas without natural predators. The common predators of marine mammals, such as killer whales and large sharks, are rarely (if ever) found in habitats inhabited by this species.

Communication

Based upon their behavior, Bauer et al. (2010) suggest that manatees may share the characteristic of pheromonal communication with their relative, the elephant. Some scientists (Rathbun, Reid, Bonde, and Powell, 1995) have observed that manatees form long periods of mating herds when wandering males come across estrous females, which indicates the possibility that males are able to sense the estrogen or other chemical indicators.[31][32] Other scientists (Sousa-Lima, Paglia, and Fonseca, 2002) have observed that manatees can communicate information to each other through their vocalization patterns.[33] Evidence suggests that there are sex and age-related differences in the vocalization structure of common squeaks and screeches in adult males, adult females, and juveniles.[34][35] This may be an indication of vocal individuality among manatees.[35] An increase in Manatee vocalization after a vocal playback stimulus shows that they may be able to recognize another Manatee's individual voice.[35] This behavior in manatees is found mostly between mother and calf interactions.[36] However, vocalization can still be commonly found in a variety of social interactions within groups of manatees, which is similar to other aquatic mammals.[36][37] 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.[38] Based on acoustic and anatomical evidence, mammalian vocal folds are assumed to be the mechanism for sound production in manatees.[39] 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.[31]

Diet

Manatees are obligate herbivores that feed on over 60 species of aquatic plants in both fresh and salt water. In addition, when the tide is high enough, they will also feed on grasses and leaves.[40] They also consume some fish and small invertebrates. While many manatees are known to eat a large quantity throughout the day, the amount they eat depends on their body size and activity level.[41] Manatees typically graze for 5 or more hours per day consuming anywhere from 4% to 10% of their body weight in wet vegetation per day. Because manatees feed on abrasive plants, their molars are often worn down and are replaced many times throughout their lives, so they are called "marching molars".The molar teeth are similar in shape, but of varying sizes. Replacement of the molar teeth are done so in the forward direction. Manatees do not have incisors. In fact, the incisors have been replaced by horny gingival plates.[42]

Manatees are nonruminants with an enlarged hindgut. 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 7 days).[43] Having an increased rate of digestion is beneficial by increasing the digestibility of their diet. It is suggested that chronic fermentation may also provide additional heat and is correlated with their low metabolic rate.[40]

Vibrissae

Sculpture of manatee showing vibrissae
All the hairs of the manatee may be vibrissae

Manatees have sensitive tactile hairs that cover their bodies and faces called vibrissae. Each individual hair is a vibrissal apparatus known as 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.[44]

Usually vibrissae are found on the facial regions of terrestrial and non-sirenian aquatic animals and are called whiskers. 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 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.[45][46]

Research has found that 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 system.[44]

Reproduction

Male manatees reach sexual maturity at 3-4 years of age, while females reach sexual maturity at 3-5 years of age.[47][48] 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.[49] Larger males, presumably older, have been observed to dominate mating herds and are likely responsible for most successful copulation events.[50]

The gestation period in manatees lasts for 12-14 months, after which they give birth to one calf at a time, or rarely twins.[50] When a calf is born, it usually weighs 60–70 lb (27–32 kg) and is 4.0–4.5 ft (1.2–1.4 m) long. Manatees do not form permanent pair bonds and the male contributes no parental care to the calf, which remains with the mother for up to two years prior to weaning. A single female can reproduce once every 2-3 years.[48] Wild manatees have been documented producing offspring into their late 30's, and a female captive manatee has given birth in her 40's.[51]

Manatee conservation

Manatees in a conservation project in Brazilian northeastern coast

The West Indian manatee has been hunted for hundreds of years for meat and hide, and continues to be hunted in Central and South America. Illegal poaching, as well as collisions with vessels, are a constant source of manatee fatalities. Additionally, environmental stresses such as red tide and cold waters cause several health problems to manatees such as immunosuppression, disease, and even death.[52]

The Florida manatee subspecies (T. m. latirostris) was listed in October 2007 as endangered by the International Union for the Conservation of Nature (IUCN) on the basis of a population size of less than 2,500 mature individuals and a population estimated to be in decline by at least 20% over the next two generations (estimated at about 40 years) due to anticipated future changes in warm-water habitat and threats from increasing watercraft traffic over the next several decades.[53]

According to the US Fish & Wildlife Service (FWS) and the Florida Fish & Wildlife Conservation Commission, the IUCN "endangered" category is equivalent to the US Endangered Species Act (ESA) category of "threatened". In 2013 the manatee was listed under the ESA as "endangered," which is equivalent to the IUCN category of "critically endangered."[54] In April 2007, the US Fish and Wildlife Service advised the species be reclassified as threatened rather than endangered. The Florida Fish & Wildlife Conservation Commission no longer includes the manatee on its list of state imperiled species.[55]

In 2007, the Florida Manatee Biological Review Panel presented their assessment of the Florida Manatee for the year 2005-2006.[54]: 13  They reported that there were no "statistically-based estimates (with variance) of abundance for the entire Florida manatee population" and that the highest count obtained from surveys undertaken since 1991, was "3300 manatees in January 2001."[54]: 12  The 2007 Biological Review Panel assessment confirmed that the greatest threat to the Florida manatee population was the potential future loss of warm-water habitat.[54] The West Indian manatee has a high casualty rate due to thermal shock from cold temperatures. During cold weather, many die due to their digestive tracts shutting down at water temperatures below 20 °C (68 °F). The Florida manatee is a tropical species unable to tolerate water temperatures below 20 °C (68 °F).[56] During the winter months, over 300 manatees often congregate near the warm water outflows of power plants along the coast of Florida instead of migrating south as they once did, causing some conservationists to worry that manatees have become too reliant on these artificially warmed areas.[57][58] According to the Florida Fish and Wildlife Conservations Commission (2010), a recorded 237 manatees died that year with 42% of those fatalities being a result of cold stress syndrome.[31] The US Fish and Wildlife Service is trying to find a new way to heat the water for manatees that are dependent on plants that have closed. According to Alvarez-Aleman et al. (2010), the first known Florida manatee was recorded utilizing the warm waters expelled by a power plant canal in Cuba in July 2006 and the following year in January, February, and April, a mother manatee and her calf were reported at the power plant in Havana, Cuba.[58]

Many manatee deaths are caused by both large and small boats. Manatees are also at a disadvantage because they are not able to quickly move away from an oncoming boat.[59]

Thirty-eight percent of manatee deaths, between the years 1995 and 2005, were caused by human-induced activities such as boats, water control devices, fishing equipment, and toxic chemicals;[60] therefore, conservation strategies involving effective public education programs and public policy enforcement are useful to manage these anthropogenic-induced fatal tragedies. Researchers strongly suggest that manatees' oral temperature, heart rate, and respiration rate should be strongly monitored during all human interventions such as field research, rescue, and captivity. Additionally, since studies have shown that death does not appear to be a common result of capture, it is believed that capture and care is necessary for manatees inhabiting Florida, Puerto Rico, and Belize.[61] One conservation strategy in maintaining viable population size is manatee rehabilitation. According to The Society for Conservation Biology (2010) the four goals of manatee conservation include conservation science, conservation management, education, and policy.[61]

According to Martine de Wit in 2017, manatee veterinarian with the FWC's Fish and Wildlife Research Institute, "We know that watercraft-related mortality is still the main threat to manatees long-term".[62] By 2007, watercraft collisions accounted for about 25% of all documented manatee deaths and was "the single greatest known cause of mortality" and the greatest limiting factor to the speed at which the manatee population could recover from stochastic events.[54]: 13  In 2016, 104 manatee deaths were water-craft related. In the same year, 520 dead manatees were found in waterways across Florida, "the third deadliest year since record-keeping began" according to Florida Fish and Wildlife Conservation Commission.[63][62]

West Indian manatee skeletons on display at the North Carolina Museum of Natural Sciences in Raleigh, North Carolina

Agencies responsible for administering the US Endangered Species Act are obliged to provide updates to the Manatee Core Biological Model every five years. The 2013 the authors of "Manatee Core Biological Model" concluded that in Florida, "statewide, the likelihood of a 50% or greater decline in three manatee generations was 12%; the likelihood of a 20% or greater decline in two generations was 56%."[64]: 41  The Core Biological Model and a related manatee threats analysis, prepared by the US Geological Service for the US Fish & Wildlife Service, represented a significant improvement in data collection and analysis.[64] The models project that the "estimated probability that the statewide population will fall below 1000 animals within 100 years was 2.3%."[64]: 41 

According to the Pacific Legal Foundation (PLF), USFWS failed to follow-up on its 2007 report by Haubold et al. by drafting a downlisting proposal for the manatee from endangered to threatened. On behalf of Save Crystal River, PLF petitioned the FWS to downlist the manatee.[65][66] The species were reclassified federally by the US Fish and Wildlife Service on March 30, 2017 from endangered to threatened as the number of sea cows had increased from a few hundred in the 1970s to over 6,000 in the 2010s.[63][67] According to Save the Manatee Club the USFWS decision 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.[68]

USFWS announced that the manatee is still protected under the Marine Mammal Protection Act and that all federal protections for the manatee remain in place.[63] Until being removed from the endangered list, Manatees received protection from the US Endangered Species Act of 1973. The West Indian manatee is still protected by the Florida Manatee Sanctuary Act of 1978 and the US Marine Mammal Protection Act of 1972.

Sonar technology is also aiding in the West Indian Manatee conservation. Side Scan technology was first introduced in the 1960s, and within the past 20 years, it has been used to aid in manatee conservation. There are currently four ways side scan is being used to research and aid in conservation. These are to aid in detection other than visually, determine group sizes and mother-calf relationships, determining habitat preferences and detection, and assisting in manatee captures. It has been shown that this technology produces a much more accurate detection percentage (>80%) than simply visual detection. Future implications include better estimates of populations and population dynamics.[69]

Quasi-extinction Risks

In 2016, the US Geological Survey, in cooperation with the Florida Fish and Wildlife Conservation Commission, conducted a comprehensive review of the Core Biological Model that is used to analyze the population viability of the Florida manatee (Trichechus manatus latirostris). The review was intended to garner information that would better assess the status and severity of threats that are posed to the FL manatee subspecies. Findings suggest that within the next 100 years the probability for either of Florida’s manatee populations, East or Gulf coast, to fall below 500 adults is approximately 0.42%.[70]

Contributing sources of mortality to the population viability analysis estimate include three quasi-extinction risks: warm water habitat loss, watercraft mortality, and red tide mortality.[70] Quasi-extinction risks, those that would result in the loss of greater than 95% of the population of Florida manatees, are thought to be low for the subspecies for three reasons:

  1. Carrying capacity for all groups of Florida manatees combined is thought to be much greater than the current total population estimate
  2. Adult survival rates are generally high
  3. Current population estimates for both coasts exceeds 2500 individuals

Despite the low probability of occurrence, watercraft-associated mortality was found to be the most significant driver of population losses at the coastal or statewide level and poses the greatest threat of quasi-extinction.[70] Because adult survival rates are so strong, the USGS concluded that active population monitoring and management would be able to prevent such scenarios from occurring and that it is likely that the Florida manatee will remain a vibrant part of Florida's natural systems throughout the 21st century.[70]

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