Animal Info - American Manatee

(Other Names: Caribbean Manatee, Lamantin d'Amérique du Nord, Lamantin des Antilles, Lamantin des Caraïbes, Lamantine, Lamantino Norteamericana, Manatí, Manatí Norteamericano, North American Manatee, Peixe-boi, Peixe-Boi-Marinho, Sea Cow, Sekoe, Vaca Marina, West Indian Manatee)

Trichechus manatus

Status: Vulnerable

Contents

1. Profile (Picture)
2. Tidbits
3. Status and Trends (IUCN Status, Countries Where Currently Found, Taxonomy, Population Estimates and Status, History of Distribution, Threats and Reasons for Decline)
4. Data on Biology and Ecology (Size and Weight, Habitat, Age to Maturity, Gestation Period, Birth Season, Birth Rate, Early Development, Dispersal, Maximum Reproductive Age, Maximum Age, Diet, Behavior, Social Organization, Age and Gender Distribution, Mortality and Survival)
5. References

Profile

Pictures: American Manatee #1 (56 Kb GIF) (Wildl. Trust); American Manatee #2 (112 Kb JPEG)

The American manatee is a large, cylindrically shaped mammal, with forelimbs modified into flippers, no free hindlimbs, and the rear of the body in the form of a flat, rounded, horizontal paddle. It may reach a length of up to 4.6 m (15') and a weight of up to 1,650 kg (3,630 lb). A manatee vaguely resembles a walrus without the tusks. Its skin is gray, wrinkled, and rubber-like. The gray color of the skin is often obscured by algal growth, barnacles or other incrustations on the skin. The manatee's body is covered with sparse hairs, and its lips are covered with bristles. Its flexible flippers are used to help it move along the bottom of its habitat and for scratching, touching and even embracing other manatees. Its upper lip is deeply divided by a vertical cleft. The manatee can move each side of the upper lip independently while feeding. It uses this  flexible upper lip, together with its forelimbs, to manipulate food into its mouth. 

The American manatee occurs in coastal waters and slow-moving rivers with a salinity ranging from saltwater to freshwater and with a depth usually from 1.5 - 6 m (5 - 20'). It seems to prefer water temperatures above about 20 deg C (68 deg F). The American manatee feeds opportunistically on a wide variety of submerged, floating, and emergent vegetation, including submerged rooted sea grasses, emergent vascular plants, benthic algae, and mangrove. It is entirely aquatic, never leaving the water, and is both diurnal and nocturnal. Generally, the American manatee is considered to be a weakly social, essentially solitary species. The only lasting association seems to be that between a cow and her calf, although temporary, casual groups of 2 - 6 animals or more may congregate in favored spots. 

Historical accounts indicate that the American manatee probably is as geographically widespread today as it was in the past, although much reduced in numbers. In the USA, manatees occur in coastal waters and rivers of the Southeast, primarily in Florida and Georgia. Outside of the USA, American manatees occur in the Bahamas, Greater Antilles and Trinidad and Tobago; the east coasts of Mexico and Central America; the northern coast of South America from Colombia to the mouth of the Amazon in Brazil; and the drainages of the Rios Cauca and Magdalena in Colombia and the Orinoco in Venezuela.  

Commercial exploitation of the American manatee began in the 16th century, and, together with extensive subsistence hunting, has resulted in severely reduced populations in most areas. The American manatee continues to decline in many areas from more recent threats, such as pollution, habitat alteration, drowning in fish nets and damage from the propellers of powerboats. Periodic red tide blooms have also been associated with a number of manatee deaths. 

Tidbits

*** It is generally believed that legends of mermaids - half woman, half fish - arose with manatees, although the resemblance to human females is difficult to discern. The order that includes manatees, Sirenia, is named for these legendary female "sirens." It is supposed that the three "mermaids" that Columbus reported in his ships' logs were American manatees, the first record of the species in literature. (Allen 1942, Beletsky 1999)

*** "There was a high level of awareness about manatees and their protected status among residents of Belize. ... Much credit may ... be due to the educational efforts of Belizean conservation groups including the Belize Audubon Society, Belize Center for Environmental Studies, and the Belize Zoo. The Zoo’s manatee conservation education efforts are to our knowledge the strongest of any local organization in the Caribbean region." (O'Shea & Salisbury 1991)

*** The manatee does not have incisors or canine teeth, only cheek teeth (molars). Molars designed to crush vegetation form continuously at the back of the jaw and move forward as older ones become worn down. The older ones eventually fall out, while new ones come in at the rear of the jaw to replace them. 

*** In areas such as Florida, manatees are frequently run over by motorboats. This usually either kills the manatee or inflicts wounds on its back that subsequently develop distinctive scars. Biologists studying manatee populations use the distinctive scars as a way of identifying individual manatees.

*** The Maya had a special process to prepare dried manatee meat, which they called "buccan". Pirates who preyed upon the ships of Spanish explorers along the Guatemalan coast relied so much upon "bucan" as a staple in their diet that they became known as "buccaneers". (Janson 1980)

Status and Trends

IUCN Status:

Countries Where the American Manatee Is Currently Found:

2004: Occurs in Bahamas, Belize, Brazil, Colombia, Costa Rica, Cuba, Dominican Republic, French Guiana, Guatemala, Guyana, Haiti, Honduras, Jamaica, Mexico, Nicaragua, Panama, Suriname, Trinidad and Tobago, USA, and Venezuela. (IUCN 2004)

Taxonomy:

There are three species of manatees: the Amazonian manatee (Trichechus inunguis), the American manatee (Trichechus manatus), and the West African manatee (Trichechus senegalensis). The American manatee is externally indistinguishable from the West African manatee. On the other hand, both the American and West African manatees can easily be distinguished from the Amazonian manatee, because they lack the distinctive white markings on the abdomen or chest which are characteristic of  the latter species.  

*** Two subspecies of the American manatee are recognized: the Florida manatee, T. manatus latirostris, which occurs in the southeastern USA, and the Antillean manatee, T. manatus manatus, which is found throughout the remainder of the species' range.  The two subspecies are indistinguishable in the field.

Population Estimates and Status:

[Note: Figures given are for wild populations only.]

History of Distribution:

Historical accounts indicate that the American manatee probably is as geographically widespread today as it was in the past, although much reduced in numbers. In the USA, manatees occur in coastal waters and rivers of the Southeast, primarily in Florida and Georgia. The large Florida population appears to be divided into at least two virtually separate and roughly equal subpopulations - one centered along the Atlantic Coast and the other on the Gulf of Mexico coast of Florida. Analyses of individual manatee locations utilizing photoidentification of individuals based on their patterns of scar tissue (resulting from collisions with boats) and radio-tracking data have shown no intermixing of these two subpopulations.  However, genetic analysis reveals little variation between the genetic characteristics of the two subpopulations, and it seems likely that there is occasional movement of some animals between the two coasts that remains undocumented. (US Fish & Wildl. Serv. 1993a)

Outside of the USA, American manatees occur in the Bahamas, Greater Antilles and Trinidad and Tobago; the east coasts of Mexico and Central America; the northern coast of South America from Colombia to the mouth of the Amazon in Brazil; and the drainages of the Rios Cauca and Magdalena in Colombia and the Orinoco in Venezuela.  Populations have been reported from river drainages up to 800 km (500 mi) from the coast.  Its range extends up the Orinoco River to the first cataract. (Eisenberg & Redford 1999, Emmons & Feer 1997, Husar 1978a, Nowak 1999)

Distribution Map for American Manatee (4 Kb GIF) (Huffman 2004)
Distribution Map for all Sirenia (Dugong and Manatee Species) (22 Kb GIF) (Wildl. Trust)

Threats and Reasons for Decline:

Commercial exploitation of the American manatee began in the 16th century, and, together with extensive subsistence hunting, it has resulted in severely reduced populations in most areas. The manatee was heavily hunted for its meat as well as for its hide, oil and bones (used as charms) which were said to possess curative properties. The American manatee continues to decline in many areas from more recent threats, such as pollution, habitat alteration such as the draining of marshes and the silting up of coastal feeding grounds, drowning due to incidental entanglement in fish nets and damage from the propellers of powerboats. Periodic red tide blooms have also been associated with a number of manatee deaths. Red tide toxins accumulate in sea squirts which adhere to sea grasses. This poison is ingested incidentally by manatees feeding on sea grasses. (Burton & Pearson 1987, Ceballos & Navarro 1991, Nowak 1999, O'Shea & Salisbury 1991, US Fish & Wildl. Serv. 1993a)

Data on Biology and Ecology

Size and Weight:

An adult American manatee averages about 3.5 m (11.5') in length and 1000 kg (2,200 lb) in weight. It may reach a length of up to 4.6 m (15') and weigh up to 1,650 kg (3,630 lb). (US Fish & Wildl. Serv. 1993a)

Habitat:

The American manatee occurs in waters that have a salinity ranging from saltwater to freshwater and that have sufficient depth (1.5 m (5') to usually less than 6 m (20')). It may be found in canals, rivers, estuarine habitats, offshore cayes, coastal lagoons and saltwater bays. Individual manatees on occasion have been observed as much as 6 km (3.7 mi) off the Florida Gulf coast and up to 15 km (9.3 mi) off the Guyana coast. The American manatee also seems to prefer water temperatures above about 20 deg C (68 deg F). Although they can endure water as cold as 13.5 deg C (56 deg F), as the water temperature drops below 15.5 deg C (60 deg F), manatees become sluggish and stop eating. Young manatees are especially susceptible to the effects of cold temperatures. (Beletsky 1999, Nowak 1999, US Fish & Wildl. Serv. 1993a)

The American manatee is one of the species that live in the Caribbean Biodiversity Hotspot (Cons. Intl.) as well as in the Central American Mangroves, Mesoamerican Reef, Mexican Mangroves, Northeast Brazilian Coast Marine Ecosystems, Orinoco-Amazon Mangroves & Coastal Swamps, and Southern Caribbean Sea Global 200 Ecoregions. (Olson & Dinerstein 1998, Olson & Dinerstein 1999)

Age to Maturity:

Females: 3 - 4 years, with first calving as early as 4 - 5 years; males appear to reach full reproductive maturity at 9 - 10 years.

Gestation Period:

12 months.

Birth Season:

Breeding may occur at any time of year but is often locally seasonal. For example, in the State of Tabasco, Mexico, reproduction occurs in the wet season, coinciding with higher water levels and increased food availability in inland lagoons and rivers. (Reid 1997)

Birth Rate:

One calf is born every 2 - 5 years, with an average interval between births of 3.0 years. Age-specific fecundity: 0.24 female calves/adult female/year based on both pregnancy and lactation data from the age of first parturition throughout life. (Marmontel et al. 1997, O'Shea & Salisbury 1991)

Percent of females with different sized litters: 57.67 % with litters of size 0; 40.64 % with litters of size 1; 1.69 % with litters of size 2 (Florida, USA population). (Marmontel et al. 1997)

Early Development:

Within half a day of birth, a manatee calf is capable of swimming and surfacing on its own, although it occasionally rides on its mother’s back. The calf begins to eat some vegetation at about 1 - 3 months, although it continues to suckle until leaving its mother at about 1 - 2 years. (Nowak 1999)

Dispersal:

A calf leaves its mother at about 1 - 2 years (Nowak 1999).

Maximum Reproductive Age:

One American manatee has been reproductively active for 35 years (captivity) (Nowak 1999).

Maximum Age:

One American manatee is estimated to have reached an age of 59 years in the wild. A captive American manatee has lived at least 44 years. (Nowak 1999)  

Diet:

The American manatee feeds opportunistically on a wide variety of submerged, floating, and emergent vegetation. It may browse on plants hanging over the water if it can reach them. Its diet includes submerged rooted sea grasses, emergent vascular plants, benthic algae, mangrove, and floating plants. Manatees also forage opportunistically on floating food items such as acorns. (Eisenberg & Redford 1999, US Fish & Wildl. Serv. 1993a)

An average American manatee eats approximately 33.2 kg/day (73 lb/day), or from 4 - 9 % of its body weight per day, depending on the season (US Fish & Wildl. Serv. 1993a). 

Although the American manatee is primarily herbivorous, some invertebrates are ingested together with vegetation and may provide an important amount of protein. Captives have deliberately eaten dead fish, and wild individuals off Jamaica have been seen to take fish entangled in nets. (Nowak 1999)

Behavior:

The American manatee is entirely aquatic, never leaving the water.  It is both diurnal and nocturnal.

Animals generally swim 1 - 3 m (3.3 - 10') below the surface of the water. The deepest recorded dive is 10 m (33').  Speed normally is 3 - 10 km/hr (2 - 6 mi/hr) but can reach 25 km/hr (16 mi/hr) for short distances (less than 100 m (330') when the animal is pressed. Average submergence time is about 4 minutes, but a dive of more than 16 minutes has been recorded. (Husar 1978a, Nowak 1999)

American manatees communicate with each other by emitting sounds underwater that are audible to humans. The vocalizations, which sound like squeaks and squeals, are especially important for maintaining contact between mother and calf. (US Fish & Wildl. Serv. 1993a)

Adults have been observed to feed 6 - 8 hours/day in sessions that usually lasted 1 - 2 hours, to rest 6 - 10 hours/day, and to move as much as 12.5 km (8 mi) in a day. (Nowak 1999)

Shallow sea grass beds with ready access to deep channels are preferred feeding areas. American manatees often use secluded canals, creeks, embayments, and lagoons, particularly near the mouths of coastal rivers and marshes, for feeding, resting, playing, mating, and calving. In estuarine and brackish areas, natural and artificial fresh water sources are sought. (US Fish & Wildl. Serv. 1993a)

Most manatees appear to be nomadic and to move hundreds of kilometers, pausing for days, weeks, months, or seasons in estuaries and rivers that supply their needs. They follow established travel routes. There is also evidence of long-range, offshore migrations between manatee population centers. Individuals have been observed as much as 6 km (3.7 mi) off the Florida Gulf coast and 15 km (9 mi) off the coast of Guyana. They also have been reported in rivers 230 km (140 mi) from the sea in Florida, USA and 800 km (500 mi) from the coast in South American rivers. (Nowak 1999) One individual from the Florida, USA population, nicknamed "Chessie," migrated as far north as Chesapeake Bay in 1994, was captured and returned to Florida, then migrated back even farther north to Rhode Island, USA in 1995, finally returning to Florida on its own. (Willis 1996). 

Social Organization:

Generally, the American manatee is considered to be a weakly social, essentially solitary species. The only lasting association seems to be that between a cow and her calf. Temporary, casual groups of 2 - 6 animals or more may congregate in favored spots for purposes of migration, feeding, resting, or playing. Such groups may be randomly made up of juveniles and adults of both sexes. There is no evidence of a communal defense or mutual aid and little or no indication of a social hierarchy. (Husar 1978a, Matola 1995, Nowak 1999)

Breeding takes place when one or more males (up to 17) are attracted to an estrus female to form an ephemeral mating herd. Such herds may remain together from a few hours to a few weeks. Permanent bonds between males and females do not form. (US Fish & Wildl. Serv. 1993a)

Age and Gender Distribution:

An extensive study of the Florida, USA population of American manatees showed that the proportion of calves in year-round aerial surveys appeared stable and fecundity appeared constant, generally supporting the assumption of a stable age distribution (Marmontel et al. 1997).

A population of American manatees wintering in the Crystal River of Florida, USA one year contained 31 adults, 13 juveniles, and 6 calves and was divided about equally between males and females (Nowak 1999). 

Sex ratio at birth: 1:1 (Marmontel et al. 1997). The sex ratio of adults and calves at Crystal River, Florida, USA is 1:1 and is considered reflective of the population's overall sex ratio (US Fish & Wildl. Serv. 1993a). 

Mortality and Survival:

Mortality/year as a function of age (Florida, USA population): 0 - 1 year old - 28.02 %; 1 - 2 years old - 18.36 %; 2 - 3 years old - 14.05 %; 3 - 4 years old - 13.90 %; 4 - 60 years old - 9.22 % (Marmontel et al. 1997).  

References

Allen 1942, Arkive, Beletsky 1999, Bertram & Bertram 1963, Burton & Pearson 1987, Ceballos & Navarro 1991, Charnock-Wilson 1968, Cons. Intl., Curry-Lindahl 1972, Eisenberg 1989, Eisenberg & Redford 1999, Emmons & Feer 1997, Huffman 2004, Husar 1978a, Inst. Envir. Model., IUCN 1966, IUCN 1994, IUCN 1996, IUCN 2000, IUCN 2003a, IUCN 2004, Janson 1980, Lefebvre 2001, Mares & Schmidly 1991, Marmontel et al. 1997, Matola 1995, Nowak 1999, Nowak & Paradiso 1983, Olson & Dinerstein 1998, Olson & Dinerstein 1999, Oryx 1972, Oryx 1974g, Oryx 1979e, Oryx 1990f, Oryx 1991h, Oryx 1992b, O'Shea & Salisbury 1991, Reid 1997, Sirenia.org, UNEP/CEP 1995, US Fish & Wildl. Serv. 1993, US Fish & Wildl. Serv. 1993a, Wildl. Trust, Wille 1995, Willis 1996, Wood 1860

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