Natural History

The West Indian manatee is a large, gray-brown, aquatic mammal with a seal-like body tapering to a flat, paddle-shaped tail. Two small forelimbs on the upper body have three to four nails on each end. The head is wrinkled and the face has large prehensile lips with stiff whiskers surrounding the nasal cavity flaps.

They are members of the Order Sirenia found worldwide in temperate or tropical coastal waters.

Learn more about Manatee physiology, breeding, manatee myths, and about the species our manatees are part of.

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Sirenian Species

Members of the Sirenia order are found in aquatic habitats similar to that of the West Indian manatee. Because of their herbivorous nature, all are found in relatively shallow waters where sunlight can penetrate and stimulate plant growth.

The Amazonian manatee lives exclusively inland, freshwater areas, while the dugong prefers coastal and marine ecosystems. The West African manatee inhabits tropical and sub-tropical waters. The only Sirenian species to inhabit cold waters was Steller´s sea cow, hunted to extinction within 27 years of its discovery in 1741 in the Bering Strait.

Traits

West Indian Manatee - Trichechus manatus, is divided into two subspecies – each possessing 48 chromosomes – based on skull anatomical differences:

  • Florida manatee - Trichechus manatus latirostrus, reaches a possible length of 3.9 meters and weight of 1,500 kilograms. They are generally gray to dark-brown in color, with rough, bumpy skin.
  • Antillean manatee - Trichechus manatus manatus, is very close to the Florida manatee in appearance, with a maximum length of 3.5 meters and weight of 1,000 kilograms. Externally, the subspecies are indistinguishable.

Amazonian Manatee - Trichechus inunguis, the smallest of the living manatees in length with the longest recorded measurement only 2.8 meters, lives in the Amazon basin in South America. It typically bears small white or pink patches on its smooth skin. Less obvious differences include: a lack of nails on the pectoral flippers, longer flippers, smaller teeth, and a longer, narrower rostrum (anterior skull) relative to other manatee species. This species is also the only one confined to fresh water. Its total number of chromosomes is 56.

West African Manatee - Trichechus senegalensis, is roughly the same size as a West Indian manatee, but has more protruding eyes, a blunter snout, a less robust body, and a more downward-pointing rostrum. The chromosomal compliment is unknown.

Dugong - Dugong dugon, with a maximum length of 3.3 meters and weight of 400 kilograms, is remarkably different from the manatee in many ways. Dugongs have smooth skin, a split tail fluke, and tusks which erupt in post-pubescent males only. They are the most marine genus of Sirenians in habitat preference, and are the only indo-pacific sirenians alive today, due to the human-caused extinction of the Stellar’s sea cow during the late 1700’s.

Physiology

The internal anatomy of the manatee has been well understood for over a hundred years, but for many organs and organ systems, modern histological and histochemical techniques need to be applied to understand their function or physiology.

Manatee senses are well-developed, especially hearing which has been measured as a range exceeding that of humans in the low frequency range. Touch, taste, sight, and smell are all important senses for the manatee and appear to be well-developed. Further studies are in progress to determine ranges of sensitivity.

Digestion in manatees typifies the hindgut digesters, herbivores in which most cellulose breakdown occurs in the large intestine. The horse is another hindgut digester.

Kidney function in manatees has not been studied, but most scientists believe that manatees can exist for some time without fresh water, but that the animals must have access to freshwater periodically to survive. Preliminary studies suggest that manatee kidneys can produce a reasonably concentrated urine.

Breeding and Reproduction

Manatees do not form permanent pair bonds. During breeding, a single female, or cow, will be followed by a group of a dozen or more males, or bulls, forming a mating group. They appear to breed at random during this time. Although breeding and birth may occur at any time during the year, there appears to be a slight spring calving peak. Manatees usually bear one calf although twins have been recorded. Intervals between births range from three to five years. The manatee was officially declared endangered in 1973 as part of the Federal Endangered Species Act.

Quick Facts

  • Gestational Period: 12 to 14 months
  • Age of Maturity: 5 years
  • Calf Dependency: up to 2 years
  • Life Expectancy: 60 years (estimated)
  • Estimated Population: 2,000 to 2,400 (estimated)
  • Offspring: One calf per birth (twins have been reported)

Environments

Suitable habitat for the manatee must provide 4 basic elements:

  • Food
    Manatees can eat up to 10% of their body weight of vegetation daily. With that in mind, manatees must have a suitable habitat with an abundance of aquatic plants to sustain all the manatees in the area.

  • Water
    Manatee intake water occurs while eating aquatic plants as well as drinking. Manatees will travel considerable distances for fresh water.

  • Space
    Manatees require space to move about. Being migratory, the space required by manatees is influenced by seasonal change. Travel corridors, or passageways (rivers, waterways, etc.) are necessary for the manatee to move back and forth between summer and winter habitats.

  • Shelter
    Manatees must have a safe, protected area - away from harassment, boat traffic, strong current, etc.

Mermaids

MermaidEarly sailors reported seeing mermaids when in fact they were probably seeing manatees or their relatives. In ancient mythology, the word "siren" meant sea nymphs who were believed to lure sailors toward treacherous rocks and resultant shipwrecks with their mesmerizing "siren songs." "Sirenia," which names the order to which manatees and dugongs belong, originates in this myth.

With a lot of imagination that would only increase after long months at sea, manatees might resemble a human form without legs. The manatee probably helped perpetuate the myth of the existence of this and other creatures such as the St. John's River monster in Jacksonville, FL. It is believed that this snake-like creature may actually be a herd of male manatees after a female manatee, forming a line of humps in the water.