Florida Manatee

Appearance:

The Florida manatee (Trichechus manatus latirostris) is a subspecies of the West Indian manatee (Trichechus manatus) that lives in and is native to Florida. Florida manatees are large, gray, aquatic mammals. Adult manatees are typically 9-10 feet long from snout to tail (2.7-3 meters) and weigh around 1,000 pounds (453.6.6 kilograms); however, they may grow to over 13 feet long (4 meters) and weigh more than 3,500 pounds (1587.6 kilograms). At birth, a manatee calf weighs around 60 - 70 pounds. Manatees have two fore-limb flippers that they use for steering movements and to hold vegetation while eating and a large, round, flattened paddle-shaped tail that is used for swimming.

Algae often grows on the backs and tails of manatees, which makes their skin color appear green or brown. Barnacles (found mostly on coastal dwelling manatees) often leave round scars from attachment sites; movement from saltwater to freshwater habitats clears the animals of these saltwater hitchhikers. Nostrils are located above the snout and have valves that tightly close when the manatee is under water. Their small eyes have a membrane that can cover the eyes for protection. The ear openings are small and they have no external lobes. Manatees have a flexible lip pad that is used to move food into their mouth. Manatees have back teeth (molars) for chewing but no frontal teeth. Teeth are continuously lost and re-grown throughout the manatee’s life. Molars form at the back of the jaw and slowly progress to the front of the jaw where they will fall out. This is seen as an adaptation trait for feeding on vegetation that grows in sandy soils. Manatees can hold their breath up to 20 minutes when resting, but when active they surface to breathe every three to five minutes. 

Habitat:

West Indian manatees can be found along the coastal and inland waters of the southern United States, throughout the Caribbean Islands, and along the eastern coasts of Mexico and Central America and the northern coast of South America.

In the United States, the Florida manatee inhabits the state’s coastal waters, rivers, and springs. During the warmer months, some Florida manatees travel up the eastern coastline into Georgia and the Carolinas with a few animals traveling as far north as Massachusetts.

In the Gulf, Florida manatees can be found west through coastal Louisiana and are occasionally sighted as far west as Texas. Prior to winter’s coldest months, these adventurous manatees migrate back to Florida’s warm water habitats, which include artesian springs and power plant discharge canals. Florida is at the northern end of the sub-tropical manatee’s winter range and these warm-water habitats play an important role in their survival during the winter months.

Behavior:

Manatees are aquatic herbivores (plant-eaters). Also known as "sea cows," these herbivores usually spend up to eight hours a day grazing on seagrasses and other marine or freshwater vegetation, eating up to ten percent of their body weight in aquatic vegetation each day. 

Manatees use their tail in an up and down motion to propel themselves forward. Strong swimmers, they can reach speeds of 15 miles per hour in short bursts. Manatees rest from 2 to 12 hours a day either suspended near the water's surface or lying on the bottom in shallow areas, usually for several hours at a time.  

Like other mammals, manatees breathe air. When active, manatees must surface every three to five minutes to breathe, but can hold their breath for as long as 20 minutes when resting. The manatee's snout is often the only part of its body that emerges out of the water when it breathes. 

While people may see many manatees gathered together at winter warm water refuges during winter months, during the rest of the year manatees are semi-social as they travel around the state’s waterways in search of food, mates, or places to rest. Except for mother(cow)/calf pairs, manatees do not need to travel together although they do socialize when other manatees are encountered. 

Females (cows) reach sexual maturity between three to five years and give birth to their first calf between the ages of four and seven years old (Marmontel 1995; O'Shea and Hartley 1995; Rathbun et al., 1995), while males (bulls) reach sexual maturity between five to seven years. During the breeding season, bulls gather and pursue a cow to form a mating group and breed at different times (Bester, n.d.). Bulls are not part of the family unit and will leave a cow alone after her breeding period is over.  Manatees can breed and give birth throughout the year; however, birthing usually peaks in the spring.  Females have a 13 month gestation time, and have a low reproductive rate, giving birth to an average of one calf every three to five years. The calf will stay with the mother for up to two years. Of the wild manatees that reach adulthood, only about half are expected to survive into their early 20s. In captivity, a manatee may live over 65 years.

Threats

The main threats to manatees are collisions with boats and the loss of warm water habitat. Manatees feed and rest in shallow waters, which makes them vulnerable to interactions with boats. Boat related manatee deaths are caused by cuts from propellers, impacts from the hull or lower unit of the motor, or a combination of the two.  The loss of warm water refuges is seen as a serious long-term threat to the continued existence of the manatee (U.S. Fish & Wildlife Service 2001). Due to the inability to regulate their body temperature (thermoregulate) in cold water, cold stress is a serious threat to the manatee (Irvine 1983).

Habitat loss is also an issue as coastal development and pollution can destroy seagrass beds and freshwater aquatic vegetation, which is the main food source of manatees. Manatees are also at risk of becoming entangled in monofilament line (fishing line) and crab trap lines which lead to injury, rescues, and death in extreme cases. Large ships may crush manatees on the bottom of waterways or between the vessel and the pier. Periodically, manatees will get crushed in flood gates and canal locks or trapped in culverts where they either drown or starve. Other threats include diseases, natural disasters, and red tide

Conservation and Management

The West Indian manatee is protected as a threatened species by the Federal Endangered Species Act, by the U.S. Marine Mammal Protection Act and the Florida Administrative Code - Florida Manatee Sanctuary Act (FMSA) (FAC 68C-22). The FMSA allows the State to set restrictions on boat speed and access in important manatee habitats. FWC enforces these boating restrictions along with Federal and local government partners.

State Management Plan
Federal Recovery Plan

Other Informative Links

Florida Manatee Program
FWC Manatee Research 
U.S. Fish and Wildlife Service Species Information
U.S. Geological Survey

References