Animal Diversity Web

Ge­o­graphic Range

The West In­dian man­a­tee or sea cow (Trichechus man­a­tus) is com­monly found in shal­low coastal areas, but can also be found in shal­low rivers, es­tu­ar­ies, and canals. In the United States this species is con­cen­trated around Florida in the win­ter months and mi­grates as far north as Vir­ginia and as far west as Louisiana in sum­mer months. The range of this species ex­tends through the Caribbean, along the east­ern coast of Cen­tral Amer­ica and the north­ern coast of South Amer­ica as far as north­east­ern Brazil. ("The West In­dian Man­a­tee in Florida", FPL. 1989; Rath­bun, 1990)

• Biogeographic Regions
• nearctic
  • native
• neotropical
  • native
• antarctica
  • native
• atlantic ocean
  • native

Habi­tat

West In­dian man­a­tees are ca­pa­ble of with­stand­ing large changes in salin­ity and move freely be­tween fresh­wa­ter and ma­rine habi­tats. They can be found in shal­low rivers, canals, salt­wa­ter bays, es­tu­ar­ies and coastal areas. Be­cause of their ex­tremely low meta­bolic rate and ab­sence of a thick layer of in­su­lat­ing body fat, they are re­stricted to trop­i­cal and sub­trop­i­cal wa­ters.

This species may in­habit clear or muddy wa­ters. Be­cause of their large size, man­a­tees pre­fer water reach­ing at least 1 to 2 me­ters in depth. These an­i­mals are most com­monly found trav­el­ling in wa­ters 3 to 5 me­ters deep and wa­ters over 6 me­ters are gen­er­ally avoided.

If the water is deep enough and the cur­rents are not too strong (under 5 kilo­me­ters per hour), man­a­tees are ca­pa­ble of trav­el­ling large dis­tances up­stream on in­land rivers. In St. John's river, man­a­tees live up to 200 km away from the ocean. Man­a­tees found in the Gulf of Mex­ico are rarely more than a kilo­me­ter from the mouth of a river.

(FPL 1989, Rath­bun 1990)

• Aquatic Biomes
• rivers and streams
• coastal

Phys­i­cal De­scrip­tion

The av­er­age body length of an adult West In­dian man­a­tee is ap­prox­i­mately 3 me­ters but some in­di­vid­u­als can reach a length of 4.5 me­ters in­clud­ing the tail. The av­er­age weight of these man­a­tees ranges be­tween 200 and 600 kg, how­ever the largest in­di­vid­u­als can weigh up to 1,500 kg. These upper fig­ures are un­usual in man­a­tees and fe­males gen­er­ally reach greater lengths and weights than the males of the species. New­borns mea­sure be­tween 1.2 and 1.4 me­ters and weigh ap­prox­i­mately 30 kg. The adults are grey or brown whereas new­borns are darker, a col­oration they lose at about one month.

Man­a­tees are some­what seal-shaped with fore­limbs (flip­pers) adapted for a com­pletely aquatic life and no hind limbs. Lungs ex­tend the length of the an­i­mal's body, which is im­por­tant in con­trol­ling po­si­tion in the water col­umn. Hair is dis­trib­uted sparsely over the body and the sur­face layer of skin is con­tin­u­ally slough­ing off. This is be­lieved to re­duce the build-up of algae on their skin.

(FPL 1989, Rath­bun 1990)

• Other Physical Features
• endothermic
• homoiothermic
• bilateral symmetry

• Sexual Dimorphism
• female larger

• Range mass

  200 to 1500 kg

  440.53 to 3303.96 lb

• Average mass

  400 kg

  881.06 lb

• Range length

  4.5 (high) m

  14.76 (high) ft

• Average length

  3 m

  9.84 ft

• Average basal metabolic rate

  70.0056 W

  AnAge

Re­pro­duc­tion

Al­though in­di­vid­u­als of this species are largely soli­tary, mat­ing herds form when a fe­male is in es­trus. These groups are made up of bulls pur­su­ing the sex­u­ally re­cep­tive fe­male. Court­ing bulls es­tab­lish a dom­i­nance hi­er­ar­chy for mat­ing rights while the fe­male at­tempts to avoid these males dur­ing most of her es­trus cycle.

Fe­males may at­tract up to 20 males, which pur­sue her for one week to one month.

Males reach full re­pro­duc­tive ma­tu­rity be­tween the ages of 9 and 10, but they are ca­pa­ble of mat­ing as early as 2. Fe­males are ca­pa­ble of re­pro­duc­tion at 4 to 5 years of age. Young fe­males lack the skills nec­es­sary to raise calves and are less suc­cess­ful breed­ers. Most fe­males breed suc­cess­fully be­tween the ages of 7 and 9. Ges­ta­tion pe­ri­ods for West In­dian man­a­tees range from 12 to 14 months and calves are de­pen­dent on their moth­ers for about 2 years. One calf is pro­duced at a time, how­ever twins have been oc­ca­sion­ally recorded. The in­ter-birth in­ter­val is 3 to 5 years, but this pe­riod may be short­ened in the event of the early death of a calf. Calves nurse un­der­wa­ter from teats near the fore­limbs. Calves are born with both mo­lars and pre­mo­lars and can begin con­sum­ing plants soon after birth, usu­ally within the first 3 weeks.

The mother-young pair is the only sta­ble, long-term as­so­ci­a­tion within the species. It has been sug­gested that the mother and her young can rec­og­nize each other after wean­ing and the as­so­ci­a­tion con­tin­ues, to a cer­tain ex­tent, through the subadult years of the young. This long pe­riod of parental care might aid in the trans­fer of in­for­ma­tion about mi­gra­tion routes and other learned in­for­ma­tion.

(FPL 1989, Nowak 1999, Rath­bun 1990)

• Key Reproductive Features
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual

• Average number of offspring

  1

  AnAge

• Average gestation period

  335 days

  AnAge

• Average age at sexual or reproductive maturity (female)
  Sex: female

  1278 days

  AnAge

• Average age at sexual or reproductive maturity (male)
  Sex: male

  913 days

  AnAge

Lifes­pan/Longevity

• Average lifespan
  Status: captivity

  28.0 years

  Max Planck Institute for Demographic Research

• Average lifespan
  Status: wild

  30.0 years

  Max Planck Institute for Demographic Research

• Average lifespan
  Status: captivity

  30.0 years

  Max Planck Institute for Demographic Research

Be­hav­ior

The West In­dian sea cow has evolved in areas with no nat­ural preda­tors and as a re­sult the mem­bers of this species have had no need to de­velop com­plex be­hav­iors for preda­tor avoid­ance. In ad­di­tion, the areas in­hab­ited by this species have fairly con­stant tem­per­a­tures year-round and an abun­dant food source. With­out the need for group for­ag­ing tech­niques or group de­fense, this species is largely soli­tary, oc­ca­sion­ally form­ing loose ag­gre­ga­tions.

Man­a­tees are not ter­ri­to­r­ial and do not ob­serve any so­cial hi­er­ar­chy. Most groups are tem­po­rary as­so­ci­a­tions, with­out re­gard to sex or age. One ex­cep­tion is herds of ju­ve­nile males, which are tem­po­rary groups that arise from the ex­clu­sion of such in­di­vid­u­als from re­pro­duc­tive ac­tiv­i­ties. In ad­di­tion tem­po­rary mat­ing herds de­velop when a fe­male is in es­trus.

Man­a­tees use their tail to pro­pel them­selves for­ward and are sur­pris­ingly agile in the water. They are ca­pa­ble of com­plex ma­neu­ver­ing in­clud­ing som­er­saults, rolls, and swim­ming up­side-down. They are ac­tive day and night, rest­ing for sev­eral hours at a time near the sur­face of the water or at the bot­tom. While rest­ing on the bot­tom, they rise to the sur­face to breath every few min­utes.

Man­a­tees use var­i­ous forms of com­mu­ni­ca­tion in the water. In­di­vid­u­als rub them­selves against hard sur­faces, pos­si­bly se­cret­ing a scent to con­vey in­for­ma­tion about the re­pro­duc­tive state of the res­i­dent fe­males. Man­a­tees also have an acute abil­ity to hear and squeals are often used to keep con­tact be­tween a mother and calf. Vi­sion seems to be the pre­ferred method of nav­i­ga­tion.

(FPL 1989, Nowak 1999, Rath­bun 1990)

• Key Behaviors
• motile

Com­mu­ni­ca­tion and Per­cep­tion

• Perception Channels
• tactile
• chemical

Food Habits

The snout of West In­dian man­a­tees is bent fur­ther down than other species in this fam­ily. This may be re­lated to the food habits of this species. West In­dian man­a­tees feed mainly on sea grasses grow­ing on the sea floor and the ori­en­ta­tion of the mouth aids in grasp­ing these plants. One of the unique char­ac­ter­is­tics of man­a­tees is their flex­i­ble split upper lip which is used to pass food to the mouth. Man­a­tees are op­por­tunis­tic feed­ers, eat­ing the leaves of most plants that can be ma­nip­u­lated by the upper lip. Man­a­tees may also use their flip­pers to dig up the roots of these plants. This vari­able diet is most likely nec­es­sary to meet their nu­tri­tional de­mands. Some man­a­tees may also eat in­ver­te­brates and will eat fish both in cap­tiv­ity and in the wild.

Be­cause of the low nu­tri­tional value of the plants con­sumed, man­a­tees must graze for 6 to 8 hours a day. Each day they con­sume 5-10 per­cent of their body weight, which can be over 100 kg in a large in­di­vid­ual. This low-nu­tient diet also has also con­tributed to the the de­vel­op­ment of low meta­bolic rates. Man­a­tees can sur­vive on 25% per­cent less en­ergy than a typ­i­cal mam­mal of sim­i­lar size.

Man­a­tees feed on abra­sive plants and, as a re­sult, their mo­lars are con­tin­u­ally re­placed through­out life as they wear down. Hind-gut fer­men­ta­tion is an­other adap­ta­tion to the her­biv­o­rous diet of the man­a­tee, aid­ing in break­ing down the cel­lu­lose of the plants eaten.

(FPL 1989, Nowak 1999, Rath­bun 1990)

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

For cen­turies West In­dian man­a­tees have been hunted for their meat, hide, and bones. This hunt­ing con­tin­ues in many South and Cen­tral Amer­i­can coun­tries. The do­mes­ti­ca­tion of man­a­tees has been sug­gested. Their sta­tus as an en­dan­gered species makes this an un­likely op­tion. It has also been sug­gested that man­a­tees be used as a method of aquatic weed con­trol within their range. How­ever, it has been shown that the amount of plant ma­te­r­ial con­sumed by these an­i­mals is not large enough to make this a vi­able op­tion.

As the state's of­fi­cial ma­rine mam­mal, the Florida man­a­tee (a sub­species of Trichechus man­a­tus) is of par­tic­u­lar in­ter­est to tourists vis­it­ing the area.

(FPL 1989)

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

N/A

Con­ser­va­tion Sta­tus

While man­a­tees have no nat­ural preda­tors, their num­bers are threat­ened by human ac­tiv­i­ties. Be­cause of their low re­pro­duc­tive rate, it is dif­fi­cult for the species to re­bound from a de­cline in num­bers. Al­though the pop­u­la­tion in Florida has his­tor­i­cally been hunted by Na­tive Amer­i­cans and, later, by the Eu­ro­pean in­hab­i­tants, it was never the vic­tim of com­mer­cial hunt­ing. In other parts of their range West In­dian man­a­tees have been ex­ploited com­mer­cially and, in some cases, this con­tin­ues. Al­though pro­tec­tion laws exist in coun­tries such as Costa Rica and Venezuela, il­le­gal poach­ing still oc­curs.

One of the main causes of man­a­tee mor­tal­ity is col­li­sions with mo­tor­boats. Man­a­tees are also killed in canal locks and found en­tan­gled in fish­ing nets. They are also threat­ened by the loss of (or dam­age to) sea beds due to agri­cul­tural and in­dus­trial runoff. These same pol­lu­tants have been shown to ac­cu­mu­late in the tis­sues of man­a­tees and some could be toxic to the an­i­mals.

Man­a­tee con­ser­va­tion ef­forts were ini­ti­ated as early as the eigh­teenth cen­tury, when the Eng­lish es­tab­lished Florida as a ma­rine sanc­tu­ary for the species. In 1893 a state law was es­tab­lished to pro­tect man­a­tees. At the start of the twen­ti­eth cen­tury fines were es­tab­lished for the killing of a man­a­tee. Man­a­tees are now pro­tected by the U.S. Ma­rine Mam­mal Act (1972), the U.S. En­dan­gered Species Act (1973), and the Florida Man­a­tee Sanc­tu­ary Act (1978).

(Marsh 1994, Oshea 1998, Reynolds 1995, FPL 1989)

• IUCN Red List

  Vulnerable
  More information

• IUCN Red List

  Vulnerable
  More information

• US Federal List

  Endangered

Con­trib­u­tors

Helen Ed­wards (au­thor), Uni­ver­sity of Michi­gan-Ann Arbor, Phil Myers (ed­i­tor), Mu­seum of Zo­ol­ogy, Uni­ver­sity of Michi­gan-Ann Arbor.

Ref­er­ences

FPL. 1989. "The West In­dian Man­a­tee in Florida" (On-line). Ac­cessed No­vem­ber 18, 1999 at http://​www.​fpl.​com/​html/​kid_​manateebook.​html.

Marsh, H. 1994. Siren­ian sta­tus and con­ser­va­tion ef­forts. Aquatic Mam­mals, 20(3): 155-170.

Nowak, R. 1999. Walker's Mam­mals of the World. 6th edi­tion. Bal­ti­more: John Hop­kins Uni­ver­sity Press.

Oshea, T., V. Cor­rea, M. Lud­low, J. Robin­son. 1988. Dis­tri­b­u­tion sta­tus and tra­di­tional sig­nif­i­cance of the West In­dian Man­a­tee, Trichechus Man­a­tus, in Venezuela. Bi­o­log­i­cal Con­ser­va­tion, 46(4): 281-302.

Rath­bun, G. 1990. Man­a­tees. Pp. 525-528 in B Grz­imek, ed. Grz­imek's En­cy­clo­pe­dia of Mam­mals, Vol. 4. NJ: Mc­Graw-Hill Pub­lish­ing Com­pany.

Reynolds, J. 1995. Sta­tus and con­ser­va­tion of man­a­tees, Trichechus man­a­tus man­a­tus, in Costa Rica. Bi­o­log­i­cal Con­ser­va­tion, 71(2): 193-196.