Defenders' Experts
Manatee Biology
Taxonomy
Manatees belong to the taxonomic order Sirenia, a name derived from the mythological “sirens” that lured ships into dangerous waters with their haunting songs. It is written in the logs of some early maritime sailors that manatees were mistaken for these sirens.
There are four living species of sirenians, including three species of the family Trichechidae:
- West Indian manatee (Trichechus manatus), of which there are two subspecies, the Florida and the Antillean
- West African manatee (Trichechus senegalensis)
- Amazonian manatee (Trichechus inunguis)
and one in the family, Dugongidae,
- Dugong (Dugong dugon)
All of these sirenian species inhabit tropical and subtropical waters. Stellar’s sea cow (Hydrodamalis gigas), which belonged to the family of Dugongs, was a very large sirenian that lived in the cold waters of the Bering Sea. It was discovered in 1741 and hunted to extinction within 27 years.
Mating and Reproduction
Florida manatees are generally solitary animals even though they are often seen in aggregations at warm water sites or feeding areas. Mating behavior consists of several males pursuing a female in estrus and vigorously vying for position.
Females have a gestation period of about 12-13 months, usually giving birth to a single calf that weighs about 60-70 pounds and is about 3-4 feet long. Twins are well documented but are considered rare.
The interval between calves can be anywhere from 2 to 5 years depending on the survival of the calf. Most females do not reproduce until they are at least 4-5 years old. The only true pair bond in manatees is between a mother and calf until the calf is weaned.
Manatees’ dependence on warm water is the single greatest long-term threat to their survival since man-made power plants provide refuge to up to 80% of the population and many of those power plants may go off-line in the near future. Further, human demands for water from underground sources is having an impact on the flows of warm water springs that some manatees depend on in the winter.
In recent years, many manatees on the Gulf coast of Florida have died from exposure to red tide toxin. Blooms of the toxic algae usually originate far off shore then come in to near shore and inshore areas. Manatees are affected one of two ways: they either inhale the toxin in an aerosol form when they surface to breathe or they ingest it from the plants they eat.
Diet and Habitat Needs
Sirenians are the only fully aquatic mammals that are strictly herbivorous. They can consume up to 15% of their weight in aquatic plants each day. Abundant aquatic vegetation such as healthy seagrass beds are important to sustain a healthy manatee population. Manatees have a very low metabolic rate, which is tied to the low nutrient value of the plants they feed on.
In spite of their rotund appearance, manatees have relatively little body fat. These factors result in manatees being extremely cold sensitive. They migrate to warmer waters when temperatures dip to the low 70s Fahrenheit. They cannot survive long in waters below about 63˚ (F).
In Florida, they need reliable warm water from natural springs and man-made power plants for survival in winter, and reliable food sources nearby.
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