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Biological Profiles




courtesy U.S. Geological Survey




WEST INDIAN MANATEE
Order - Sirenia
Family - Trichechidae
Genus - Trichechus
Species - manatus








Taxonomy

The manatee population in the United States is concentrated in Florida. These manatees, commonly called Florida manatees, are scientifically referred to as Trichechus manatus latirostris. They are a subspecies of the West Indian manatee (Trichechus manatus). Fossils of these magnificent animals have been found in Florida, dating back 45 million years. It is believe that the manatee evolved from a wading, plant-eating land animal. Its closest land relative is the elephant.


Common Names

West Indian manatee, Florida manatee, Caribbean cow, sea manatee, and manatee.


Geographical Distribution

Throughout most of Florida, manatees can be found in shallow, slow-moving waters of rivers, estuaries, bays, canals and coastal areas where seagrass beds thrive. They are susceptible to cold-related illness and during the winter months congregate in natural spring water, which maintains a constant temperature of 72F (22C). Throughout the remainder of the year, manatees migrate freely around Florida's river and coastal systems. The manatee may also be found inhabiting the coastal and inland waterways of Central and South America, south to Brazil.



Distribution map for the Florida manatee


Habitat

Within the state of Florida, manatees reside in a wide range of near-shore and inland habitats. These include shallow coastal waters such as estuaries and lagoons, as well as inland waterways including rivers, spring runs, and lakes. These habitats provide fresh, brackish, and salt waters of more than 3 feet (1 m) in depth. Manatees require warm waters and will migrate to warmer water when water temperatures drop below 68F (20C). They form large aggregations near industrial outfalls and natural springs during the cool winter months.
Spending most of the time feeding and resting along the bottom, manatees must surface to breathe through the nostrils. While submerged, the nostril slits remain tightly closed. Intervals between breaths are dependent upon activity level. During high levels of activity, manatees surface as often as every 30 seconds while during periods of rest, manatees have been known to remain submerged for as long as 20 minutes. The lungs are very large, located lengthwise along the backbone, extending two-thirds the length of the body. The lungs are used for buoyancy control, as well as breathing.
Manatees emit sounds believed to be a form of communication with other manatees. These vocalizations, in the form of squeaks and squeals, may express play, fear and anger or be used in courtship. They also use sounds to maintain contact with each other, especially in the case of the cow and calf.


Biology

Distinctive Features

The manatee has a seal-like body tapering to a paddle-shaped tail. The skin is thick and wrinkled with a rough texture and highly sensitive to touch. There are whiskers on the snout. The powerful upper lips are used for maneuvering food and digging through bottom sediments. There are two forelimbs on the upper body, each with three to four nails. Adult manatees swim primarily through the pumping action of the tail while the front flippers are used to steer and for lateral movement or crawling along the bottom as well as for bringing food into the mouth. Young manatees propel themselves with their flippers.
Manatees have a large digestive system to cope with an herbivorous diet. They have to constantly replace molars that are worn down from the consumption of abrasive plants. New molars form at the back of the mouth, moving forward over time, gradually pushing out the oldest, most worn teeth. These teeth are sometimes referred to as "marching molars". The rate at which this occurs depends upon how much fibrous plant material is consumed. Possessing good eyesight, manatees can distinguish between different sizes, colors, and patterns. The eyes are small and are protected by a nictitating membrane.


Manatee Taking A Breath
courtesy U.S. Geological Survey/Sirenia Project
Manatee Taking a Breath


Coloration
The manatee is a large gray-brown, uniformly colored aquatic mammal.


Size, Age & Growth
Adults may reach lengths of more than 13 feet (3.9 m) and weigh over 3,500 pounds (1,588 kg), however they more commonly average around 10 feet (3.0 m) in length and weigh around 1,000 pounds (453.6 kg). At birth, the young manatee is 3-4 feet (0.9-1.2 m) long and weighs between 60 and 70 pounds (27.2 to 31.8 kg). Calves gain approximately 700 pounds (318 kg) during their first year of life. Males reach sexual maturity at the ages between 6-9 years, while females are mature at ages of 5-9 years. They are long-lived, surviving for 60 years or more.


Food Habits
As herbivores, manatees rely almost exclusively on aquatic plants for survival. These plants thrive in the shallow and near-shore waters where there is plenty of light penetration. A favorite plant of the manatee is manatee grass (Syringodium filaforme), a seagrass that is common in saltwater habitats of the manatee. They also eat other types of seagrasses and algae as well as a large variety of freshwater plants. There is scientific evidence that manatees require freshwater to drink. While manatees are living in saltwater habitats, they actively seek out freshwater sources for drinking water.

Manatee Feeding on Sargassum
courtesy U.S. Geological Survey
Manatee Feeding on Sargassum


Reproduction
Manatee and Calf
courtesy U.S. Fish and Wildlife Service
Manatee and Calf
During breeding season, a group of males will follow the female, forming a mating group, breeding at random during this time. Breeding and birthing may occur throughout the year, however there appears to be a peak spring calving season. Gestation period is approximately 13 months, resulting in the birth of one calf, although twins have been documented. The time between births ranges from 2 to 5 years. The young calf nurses and remains dependent upon the mother for up to 2 years, learning travel routes and survival skills. Calves nurse under water from a nipple located behind the cow's flipper. They begin to feed on plants within a few weeks after birth.


Threats
Currently, the Florida manatee is listed as "endangered". It is protected by the Endangered Species Act of 1973 and the Marine Mammal Protection Act of 1972. These Acts make it illegal to harass, hunt, capture or kill this animal. The manatee is also protected by the Florida Manatee Sanctuary Act of 1978, which states, "It is unlawful for any person, at any time, intentionally or negligently, to annoy, molest, harass or disturb any manatee".
Low rate of reproduction, combined with habitat loss and high mortality rates often attributable to humans, threaten the manatee's chance of survival. There is currently between 3,000 and 3,500 manatees in Florida waters. Documented manatee mortality for the year 2001 in Florida waters totaled 325, from human-related activities and natural causes. Human-related mortality is due to loss of habitat, watercraft collision, pollution, litter, harassment, and flood control structures, while natural mortality is due to cold weather and red tides.


Watercraft Collision Injury
courtesy U.S. Fish and Wildlife Service
Watercraft Collision Injury


Conservation

Boats and Divers in Crystal River, Florida
courtesy U.S. Geological Survey/Sirenia Project
Boats and Divers in Crystal River, Florida
Many efforts have been made to protect the remaining manatees residing in Florida waters. The Manatee Recovery Plan was developed as a result of the Endangered Species Act. This recovery plan is through the US Fish & Wildlife Service, which sets forth a list of tasks toward the recovery of the manatee from its current endangered status. The Save the Manatee Club is part of this recovery plan, making recommendations to the state of Florida on manatee protection issues.

In the late 1980s, the Florida Department of Environmental Protection (FDEP) began working with counties considered to be "key" manatee areas. These counties include Duval, Volusia, Citrus, Brevard, Indian River, St. Lucie, Martin, Palm Beach, Broward, Dade, Collier, Lee, and Sarasota. These counties, in cooperation with the state, have developed site-specific boating speed zones in attempt to reduce watercraft collisions with manatees. Counties are also responsible for developing comprehensive manatee protection plans for each locale. Other measures being taken include scientific research looking at the biology, population dynamics, behavior, mortality and habitat of manatees, implementation of management plans, posting slow speed signs and fining for excess speeds in these areas, manatee education programs, and the creation of manatee sanctuaries in areas of critical habitat.


Manatee Researchers Releasing Manatee
courtesy U.S. Geological Survey/Sirenia Project
Manatee Researchers Releasing Manatee




Prepared by:
Cathleen Bester