A manatee’s age can be determined by the annual growth rings in its ear bones. Living manatees are classified as calves, subadults, and adults and age can be approximated by birth date (if known) and their size. Learn more about estimating manatee age using growth layer groups in ear bones.
Manatees’ eyes are small and they have a nictitating membrane that can be drawn across the eyeball for protection. They do not have eyelashes but rather open and close their eyes like the iris of a camera. Manatees have fairly good visual acuity and can distinguish between different-sized objects, brightness, and patterns. It is believed that manatees have rather poor visual acuity at close distance but better than expected visual acuity at medium or long distance. Manatees rely on direct contact for closer inspection, rather than on sight, which can be problematic if they encounter objects such as monofilament fishing line, discarded fishing gear, and other trash. As manatees evolved, they have adapted to live in murky waters and rely on more than one type of sensory system to investigate their underwater world. It’s safe to say that manatees do not rely on their vision as their primary sensory system, however they may utilize eyesight in combination with other senses to perceive their world in a way that benefits them beyond what we presently know.
Based on the internal structure of the manatee eye, which possesses rods and cones, manatees have color vision. Behavioral research has confirmed that they are able to see the colors blue and green against a grey background but are unable to see red. Manatees are believed to have dichromatic color vision. This characteristic is similar to that of California sea lions, fur seals, elephants, and hyraxes. Most other marine mammals have monochromatic vision. It is possible that the colors blue and green may be beneficial to enhance contrast and determine what might be edible in the manatees’ underwater world.
Manatees do indeed have teeth. In fact, one of the most interesting things about manatees is that they keep replacing their teeth as long as they live. All of their teeth are molars. Called “marching molars,” their teeth are unique because they are constantly replaced. New teeth form at the back of the jaw, wear down as they move forward, and eventually fall out. This constant tooth replacement is an adaptation to the manatee’s diet, which often includes abrasive plants that are mixed with sand.
Yes manatees do have fingernails. They typically have about three to four nails on each flipper. However, only West African and West Indian manatees, including our very own Florida manatee, have fingernails. The Amazonian manatee and the dugong do not have fingernails. Dr. Daryl P. Domning, an expert on the evolution of sirenians and a member of Save the Manatee Club’s Board of Directors explains this difference: “One could speculate that the nails might be helpful in preventing abrasion of the edges of the flippers when the animals use them to ‘walk’ along the sea bottom, as West Indian and West African manatees sometimes do; whereas the other species might do this less. Or loss of the nails may have been for no directly adaptive reason. Since the nails (if any) of fossil sirenians have not been preserved, we can’t trace the actual time and circumstances of their loss.” Having fingernails is one of the many characteristics showing the similarities between manatees and their land relative, elephants. Elephants also have three to four nails on each of their feet, like our toenails. The reason manatees have fingernails is because they were once land animals and had forelimbs for walking on land. The bone structure of a manatee’s flipper actually looks very similar to a human hand. Their flippers are simply the evolution from forelimbs that once had fingernails, which they have retained over the years.
On the whole, the sensory systems of the manatee have not been well studied. Anatomically, manatees have extremely large ear bones and may have a good sense of hearing. Manatees emit sounds underwater that are used in communicating with one another. It is not believed they are used for navigational purposes. Vocalizations may express fear, anger, or sexual arousal. They are also used to maintain contact, especially when manatees are feeding or traveling in turbid water. Especially common are vocalizations between a female and calf. Manatee sounds can be described as chirps, whistles or squeaks, have peak energies in the 3-5 kilohertz range, and are probably produced in the larynx. It has been suggested, but not confirmed, that the most sensitive location on the manatee’s head for sound reception is not the tiny ear openings located several centimeters behind the eyes, but the area near the cheek bones, which are large and seem to be quite oily compared with other bones in the skull and which are in direct contact with the ear bones. This arrangement is similar to that of dolphins. In addition, anatomical studies suggest that manatees are not adapted to hear infrasound, frequencies too low to be heard by the human ear, generally less than 20 hertz.
The peduncle is the base of the tail, right where it connects to the body of the manatee.
The average adult manatee is about 9.8 feet (three meters) long and weighs between 800 – 1,200 pounds (362-544 kilograms).
Adult manatees have been known to exceed lengths of near 13 feet (four meters) and weigh over 3,500 pounds (1,587 kilograms).
Although manatees are big, they actually have very little body fat. Aquatic mammals that live in cold areas or deep water have developed better insulation than manatees require in their tropical home. A large percentage of the manatee’s body is taken up by the gastrointestinal tract, which contains the stomach and intestines. In fact, the gastrointestinal tract accounts for about 20% of the manatee’s body mass, and it produces heat as food is digested, which helps manatees stave off the cold in the winter. Researchers believe that the manatee’s size probably evolved as a result of being aquatic and having a herbivorous (plant-eating) diet. The plants manatees eat have a low nutritional value, so they make up for that by eating large quantities of them.
Just like humans, manatees can vary in how quickly they grow and when they stop. At birth, manatees are usually approximately four feet long and weigh around 60 pounds. For the first one to two years of its life, a manatee is considered a calf and is less than eight feet long. At the age of three years, manatees usually fall into the category of “subadult” and range between about seven and a half and nine feet in length. Manatees are typically considered adults by the time they are five years of age, or approximately nine feet long, or larger. So, if a manatee is four feet long at birth and nine feet long at the age of five, that manatee may have grown one foot each year. Once a manatee reaches adulthood though, growth slows. Manatees can grow to be 13 feet long and weigh upwards of 3,000 pounds, although many adults average 10 feet in length and weigh in at approximately 1,000 pounds. Females tend to be slightly larger than males, and they certainly weigh more during pregnancy.
Manatees are capable of living long lives. In fact, it is possible for manatees to live up to 60 years or more. Because of the many perils in the wild, however, longevity is uncertain. In particular, research conducted at the Florida Fish and Wildlife Conservation Commission shows cause for concern. This research revealed that few manatees were living past the age of 30, and the majority of animals that were necropsied died between the age of 0 and 10 years — nowhere near their estimated life expectancy of 60 years.
Sadly enough, most adult manatees living in the wild bear scars from at least one watercraft collision. In fact, manatee scars are so commonplace, researchers use them as a method of individual identification.
Many manatees have “skeg” marks. A skeg is part of a motor on the boat. It extends slightly below the propeller and can sometimes come in contact with the manatee without the propeller making contact, creating a single longitudinal gash. When a manatee gets hit by a boat propeller, it also creates prop wounds which take the form of a parallel series of slash marks. If the injury is deep enough, it can be seen on the manatee forever. If the injury is superficial, it will still be there, but you wouldn’t be able to see it unless you got very close as skin would grow on top of it.
When manatees are born, they are a gray-black in color. Within a month they change to gray. Manatee adults range in color from gray to brownish-gray.
A manatee does not sweat. Instead, to regulate body temperature, a manatee can increase or decrease blood flow to its extremities, depending on if it is hot or cold. When a manatee increases blood flow to its extremities, heat loss is amplified by the underwater environment, which transfers heat 25 times faster than air. To conserve heat, a manatee can reduce blood flow to its extremities, and it also has thickened skin and fat layers to help reduce passive heat loss from its body into the water.
Manatees that are found in fresh water often have algae growing on their backs. Manatees that are found in salt water sometimes will have barnacles attached to them — just like boats found in those waters!
Manatees do not have blowholes. They breathe through nostrils, like seals. Their nostrils have fleshy “valves” that close when they are underwater.
Modern manatees evolved in the tropics and subtropics. In spite of their size, they have very little body fat. These factors may account for their susceptibility to cold water. Because manatees are herbivores, their metabolic rate is low compared with other aquatic mammals.
Manatees, like other aquatic mammals, do most of their feeding underwater and must be able to hold their breath long enough to feed efficiently. Aquatic mammals have a number of adaptations that allow them to stay under water longer than the average land-dwelling mammal. Both the lungs and diaphragm of a manatee extend the length of the body cavity and so are oriented in the same horizontal plane as the manatee in the water. This arrangement is important for buoyancy control. An unusual anatomical feature of sirenians is that each lung is in a separate cavity. Instead of one diaphram like people, manatees have separate “hemi-diaphragms.” Besides breathing, the lungs help the manatee with buoyancy control. Manatees replace a large percentage of air in their lungs with each breath and can therefore prolong intervals between breaths. In fact, studies have shown that manatees can renew about 90% of the air in their lungs in a single breath as compared to humans at rest who generally renew about 10%.
In the winter, usually November through March, manatees are concentrated primarily in Florida. Water temperatures below 21° C (70 degrees) usually cause manatees to move into these warm water refuge areas. Manatees are susceptible to cold-related disease, and they congregate near natural springs or warm water effluents of power plants. Individual manatees often return to the same wintering areas year after year. In the summer months, manatees are much more widely distributed and can be found as far west as Texas and as far north as Massachusetts, but these sightings are rare. Summer sightings in Alabama, Georgia and South Carolina are relatively common.
Historically, manatees in Florida have relied upon a number of freshwater springs during the winter months. Manatees depend on warm water sites when ambient water temperatures fall below 68 degrees Fahrenheit. Without warm water, manatees become susceptible to a condition called cold stress syndrome, which can be fatal. As Florida has become more developed, manatees have lost access to some of these springs and the amount of available warm water at other springs has been reduced as human demands for freshwater have increased. When coastal power plants were developed, which produce warm water effluent, manatees came to recognize these sites as part of their winter habitat, and a large number of manatees now use such sites. To these manatees, the power plants are a part of their habitat. However, manatees that inhabit areas of the state with fresh water springs still utilize these springs during the winter months. Natural warm water springs must be protected and sites that have become unavailable to manatees should be restored because these natural sites are a preferred habitat for Florida’s manatees.
Manatees don’t really need to get prepared for the journey, because they find their food source (seagrass and other aquatic plants) along the way.
Although aquatic mammals have much in common because of their physical structure and aquatic habitat, each is adapted to its own particular lifestyle and niche. Predators or carnivores such as orcas or dolphins, for example, must have speed, strength and weapons such as sharp, biting teeth to catch and kill prey. Manatees are herbivorous (plant eaters) and have no natural predators, so they don’t require fast swimming ability to catch prey or escape predators.
Manatees prefer waters that are about three to seven feet (one to two meters) deep. Manatees are found in both salt and fresh water. Along the coast, manatees tend to travel in water that is about 10 – 16 feet (three to five meters) deep, and they are rarely seen in areas over 20 feet (six meters) deep.
Manatees may rest submerged at the water bottom or just below the surface, coming up to breathe on the average of every three to four minutes. When manatees are using a great deal of energy, they may surface to breathe as often as every 30 seconds. However, they have been known to stay submerged for up to 20 minutes.
They aren’t. Research has shown that they actually avoid them, when they can. In fact, videotape from the Florida Fish and Wildlife Conservation Commision’s Research Institute clearly documents manatees reacting to the sound of approaching boats at various speeds.
Manatees are semi-social, somewhat solitary animals. They sometimes gather in small, informal groups, but they have no leader or real herd structure. Manatees do not form permanent pair bonds like some animal species. After breeding, the male manatee has no further involvement with the mother or calf. The mother manatee will nurse her calf for one to two years, and the calf may remain dependent on its mother during that time. The cow-calf bond is very strong throughout this period, as the mother teaches the calf important survival skills, such as migration routes, resting areas, and where to find food and warm water refuges.
Not much is known about any association between mothers and calves after the weaning period. If there is recognition, it doesn’t appear to go beyond the level of attention given to any other manatee. However, Wayne Hartley, Save the Manatee Club’s Manatee Specialist, has monitored generations of manatee families at Blue Spring State Park, and he has made some interesting observations:
- After a manatee named Beetle was weaned, he would return every few days or weeks to visit his mother Phoebe.
- Lily, one of Save the Manatee Club’s adoptees, nursed her calf Luther for two years. When she apparently lost her next calf, Luther – not some other unrelated manatee – began nursing from Lily again.
- Sometimes when Wayne does his “Manatee Roll Call” at Blue Spring, he has noticed that every member of a manatee family will be in the same vicinity in the spring run. He speculates that this could be because, as a calf, each manatee became accustomed to the location his or her mother used in the spring run and so returns to it out of habit.
Wild manatees do interact with a variety of other species. One such species is the American alligator. While many people think that alligators may be a threat to manatees, it is frequently the manatee that initiates the interaction. Some curious manatees will follow the alligators around, while the alligators try to avoid them. Another interaction that is commonly seen is the interaction with manatees and armored catfish. Armored catfish are an invasive species that have entered the Blue Spring system in Florida. They annoy the manatees, because they are frequently seen attempting to eat the algae off the back of manatees. This interaction can disturb manatees, which can be detrimental to them in the winter time when they need to be resting. Some of these different interactions between manatees and other species can be viewed on the Blue Spring webcams at ManaTV.org.
Manatees are definitely smart enough to train. They don’t have convolutions on the surface of their brain that are usually associated with higher intelligence. However, they have a higher gray matter to white matter ratio than any other mammal known, including humans! Since gray matter is the area of the brain where thinking occurs, it could be that manatees are a lot smarter even than us! More research needs to be done to understand the composition of manatee brains and how it relates to their intelligence. As far as what tricks they can perform, we think the manatee’s ability to survive in a hostile environment is a pretty neat trick in itself.
Manatees are herbivores (plant-eaters), feeding on a large variety of submerged, emergent, and floating plants. Seagrass beds and freshwater submerged aquatic vegetation are important feeding sites for manatees. Manatees can eat 10 – 15% of their body weight in vegetation daily. A 1,000-pound (453-kilogram) manatee, for example, would probably eat between 100 – 150 pounds (45-68 kilograms) of food a day. Listed below are some main types of marine and freshwater vegetation in Florida that manatees prefer to eat.
Marine Vegetation
Syringodium filiforme/Manatee grass
Thalassia testudinum/Turtle grass
Halodule wrightii/Shoal grass
Ruppia maritima/Widgeon grass
Freshwater Vegetation
Hydrilla verticillata/Hydrilla*
Vallisneria neotropicalis/Tapegrass, Eelgrass
Eichhornia crassipes/Water hyacinth
Pistia stratiotes/Water lettuce
*Non-native, or exotic, vegetation
Although manatees look fat, they actually have very little body fat for an aquatic mammal. Remember, they are a tropical species and have no need for body fat to keep them warm. A large percentage of the manatee’s body is taken up by the gut tract, which contains the stomach and intestines etc. Researchers believe that the manatee’s large size probably evolved as a result of being aquatic and having a herbivorous (plant-eating) diet. The plants manatees eat have a low nutritional value, so they make up for that by eating large quantities of them.
Although manatees are herbivores, sometimes sea squirts, mollusks, or any of several species of zooplankton can be inadvertenly eaten while the manatee feeds on seagrasses.
There are a couple of reasons the manatee might have been gnawing on the tree. It is possible that the tree had some algae on it that the manatee was eating. It is also possible the manatee just liked the way it felt. Manatees are more sensitive in their facial area than some animals, so they are more orally fixated. Either way, the manatee was not actually eating the tree or the bark. Although manatees are herbivores and only eat plant vegetation, they do not have the proper teeth arrangement to eat bark. They only have large molars in the back of their mouth, and they would need teeth in the front of their mouth in order to actually scrape off any bark from a tree.
Manatees are primary feeders (plant-eaters). They feed directly off of plants. They are comparable to ungulates like deer or cattle, who are browsing or grazing animals. Unlike their land counterparts however, manatees have no natural predators.
Manatees are herbivores, feeding on a large variety of submerged, emergent, and floating plants. Seagrass beds and freshwater submerged aquatic vegetation are important food sources for manatees. Their food sources grow in relatively clear, shallower waters. Also, the water they need to drink is close to shore. The depths at which manatees are found are likely more related to food and water location than to physiological diving limitations. Generally speaking, manatees prefer waters that are about 3 – 7 feet (one to two meters) deep. Along the coast, they tend to travel in water that is about 10 – 16 feet (three to five meters) deep, and they are rarely seen in areas over 20 feet (six meters) deep.
Although manatees are found in fresh, brackish, or salt water, they don’t drink salt water. Research suggests that manatees in salt water can go without drinking fresh water for extended periods. On average, they must return to fresh water every one to two weeks to drink. Their intake of water occurs while eating aquatic plants as well as actively drinking. This may explain why manatees can go so easily from freshwater to marine environments. It also means that people do not need to give manatees water from hoses. Manatees can take care of their own fresh water needs.
For the most part, manatees do not have any natural predators in the wild. It is often thought that animals such as sharks and alligators would be predators to this slow-moving, easy prey. While manatees, sharks, and alligators do all share the same habitat, manatees do not compete with sharks and alligators for food. Since there is no need for conflict or aggression between manatees and other animals, there is no need for predation of manatees. In addition, manatees are simply too large to be attacked by other animals. There have been a few rare incidents of manatees and manatee carcasses being predated upon by sharks and alligators, but they have mostly been small manatees or calves. But manatees must also deal with a high number of mortalities from human-rated causes. This includes deaths from watercraft, locks/canals, and other human related sources, such as discarded fishing line. In some places around the world, hunting for manatees is still a part of many cultures. Other non-human related threats to manatees are red tide and cold stress. Watch Video: Manatees and Alligators — Florida’s Odd Couple.
There is not much known about diseases in manatees. Currently, it is unknown if they are able to get the common cold (although they are very susceptible to dying from cold stress or even cold shock when they can’t reach, or there are not enough, warm-water refuges). They have been known to get diseases such as papilloma viruses, pneumonia, and upper respiratory infections. The first case of cancer in manatees was also identified a few years ago. There is a thought that manatees may not be living long enough to become susceptible to diseases seen in longer-lived mammals.
Florida laws to protect manatees were enacted as early as 1893. However, until the Endangered Species Act of 1973, there were no real laws to protect them. It is now illegal to hunt manatees in the United States, but they are still hunted in all other parts of their range. Most of the time it is opportunistic hunting, such as when the manatee accidentally wanders into a fisherman’s net and is used for food. Poaching of manatees is the United States is extremely rare, but it still occurs.
In spite of their size, manatees have relatively little body fat and cannot tolerate water temperatures below 68° F for long periods of time. In fact, manatees can die from exposure to prolonged cold weather. A cold-stressed manatee is usually malnourished and emaciated, and their body will have white patches where the skin has sloughed off. When a manatee is rescued due to cold stress, the first step is to bring the animal’s core temperature back to normal. While en route to a rescue facility, thermal blankets may be used. Upon arrival at the facility, the manatee is placed in water above 80° F. The next step is to ensure the manatee is eating. If it is not, then the manatee may need to be tube-fed. Getting nutrients is important to keep the manatee’s gut working, and it also helps with internal heat production since manatees generate heat in the digestion process due to microbes in their gut. Antibiotics may be administered to prevent the spread of infection from skin lesions associated with cold stress. In addition, cold-stressed manatees are often dehydrated and constipated, so rehydration is an important step and also helps facilitate the movement of food through the intestines.
Manatees can fast for a number of days during cold weather. Typically the cold snap will break within a week or the afternoon sun will warm enough for them to make at least a brief trip out to feed. Supplementing the manatee’s food source would change their natural behavior and affect their migration and daily routines and is not allowed by law. Protecting and enhancing warm water habitat really is the best thing we can do for them, and that is an important goal of Save the Manatee Club.
All types of boats that are going too fast are dangerous to manatees. On average, most manatees only travel about three to five miles (three to eight kilometers) per hour, so any boat that is traveling faster than 15-20 miles (24-32 kilometers) per hour is capable of injuring or killing a manatee.
Over the years, a number of people have asked this question because they were very concerned that manatees have been struck and injured by boats. There are several reasons as to why manatees cannot simply be rounded up and put in one safe location. First, manatees naturally roam over large areas of water in order to find food, suitable habitat, and, of course, other manatees. If the manatees were confined to one location — provided one was found large enough to hold all the manatees — they would not be able to continue these essential activities and maintain a balance with their natural habitat. Confining manatees to one location also has the potential of increasing disease and other abnormalities. Second, it is highly unlikely that any one location would be suitable in terms of supplying the manatees’ diverse requirements. Manatees are very sensitive to temperature changes and can only survive in waters above 68° F. Therefore, any location they were taken to would not only have to be large enough, it would also have to be consistently above 68° F. It is also unlikely that any one location would have enough food to support the entire population as manatees can eat up to 10% of their body weight in vegetation daily. Also, manatees in the wild can graze over large areas, thereby not overgrazing any one area. Third, manatees serve an important role in their aquatic ecosystem. Removing them from their natural environment would also likely disrupt the balance of the ecosystem, which could lead to adverse consequences to other organisms. Lastly, finding and safely capturing and transporting all of the manatees would be virtually impossible both financially and logistically. Such an effort, while it may seem to be helpful by keeping manatees away from boats, would certainly lead to doing more harm than good to manatees.
A synoptic survey is a statewide aerial survey designed to get a head count of individual manatees. The success of surveys is very dependent on weather conditions. If the weather is cold and clear, then manatees are gathered around warm water sites, making it easier to get a count. The synoptic surveys, which are required by Florida law, are often mistakenly used as a gauge of how the manatee population is faring, but most population scientists agree that the surveys alone cannot be used to evaluate the manatee population. No information on manatee population health and trends can be inferred from the survey count. They are simply a snapshot of the number of manatees seen on those days. Get more information on the current status of the manatee population and see synoptic survey results from previous years.
A more accurate picture of the manatee population could be obtained by looking at factors such as past and projected population trends, area of geographic range and critical habitat, the number of mature individuals, and the probability of extinction. In addition, there is ongoing research that utilizes annual adult survivability and other long term research that is better suited to assessing the health and stability of the manatee population.
Outside of Florida, little is known about the population of West Indian manatees or other sirenians in the world. By far, the largest population of West Indian manatees is found in the U.S. (Florida). Elsewhere, they are found in small population pockets throughout their range. All sirenian species in the world are listed as endangered or vulnerable by the IUCN – World Conservation Union.
No one knows how many manatees there were in the 50s and 60s because there was little or no research being done. There could have been 10,000 manatees in Florida at that time or 500. Scientific, methodical research to determine the minimum population statewide began in earnest in the early 1990s when the first synoptic aerial surveys were conducted. Each synoptic survey results in a minimum population number. However, because of extreme variability between surveys due largely to weather conditions, this does not yield a statistical estimate of the population and cannot be used for population trend analysis.
Florida manatees are found in shallow, slow-moving rivers, bays, estuaries and coastal water ecosystems of the southeastern United States. They can live in fresh, brackish or salt water. Manatees prefer waters that are about three to seven feet (one to two meters) deep. Along the coast, manatees tend to travel in water that is about 10 – 16 feet (three to five meters) deep, and they are rarely seen in areas over 20 feet (six meters) deep. This habitat provides them with sheltered living and breeding areas, a steady, easily obtainable food supply, and warm water — all of which they need to survive.
Manatees share their habitat with many living things. It is not uncommon, for example, to see a manatee swimming near a tarpon, resting next to a sea turtle, or surfacing beside a brown pelican in a marine environment. Sharks, rays, snook, snapper, flounder, and oysters are found in the manatee’s marine environment as well. However, manatees are also found in fresh water. In the manatee’s freshwater habitat, you can find river otters and fish such as largemouth bass, sheepshead, gar, and bluegills. You can also find freshwater turtles and frogs. Freshwater invertebrates would include snails, mollusks, and insects. Some species that are found in both freshwater and marine environments include ospreys, bald eagles, alligators, herons, egrets, and snakes.
Florida manatees are somewhat migratory. In the winter, usually November through march, the manatee population is concentrated primarily in Florida. Water temperatures below 70 degrees F (21 degrees C) usually cause manatees to move into warm refuge areas. Manatees are susceptible to cold-related disease, and they congregate near natural springs or warm water effluents of power plants. In the summer months, manatees are much more widely distributed. They travel freely around Florida’s rivers and coastal waters. A few manatees may range as far west as Texas and as far north as Virginia (one manatee was even documented in Cape Cod, Massachusetts), but these sightings are rare. Summer sightings in Alabama, Georgia and South Carolina are relatively common.
Like many marine mammals, it is possible for manatees to have barnacles attached to their backs. However, this is only possible if the manatee is in a salt water environment. Barnacles do not attach to manatees in fresh water and will eventually fall off once a manatee has ventured from salt to fresh water. Since manatees can be found in fresh, brackish, and salt waters, barnacles are continuously attaching and falling off a manatee’s back. A manatee’s skin is also relatively tough, making it more difficult for the barnacle to penetrate the skin to attach. In addition to barnacles, manatees can often be found with algae growing on their backs. Algae (and barnacles) will grow on a manatee’s back because manatees are such slow-moving animals. Unlike barnacles, algae can grow in salt and fresh waters, depending on the species. Therefore you are much more likely to see a manatee with algae on its back than with barnacles.
Manatees in Florida are protected by both state and federal law. They are protected by two federal laws: The Marine Mammal Protection Act of 1972 and the Endangered Species Act of 1973. Manatees are also protected by the Florida Manatee Sanctuary Act of 1978.
The Florida Manatee Recovery Plan is coordinated by the U.S Fish and Wildlife Service and sets forth a list of tasks geared toward recovering manatees from their current threatened status. These tasks include: the development of site-specific boat speed zones for manatee protection, implementation of management plans, posting of regulatory speed signs, levying fines for excessive speed in designated areas, public acquisition of critical habitat, creation of sanctuaries, manatee research, and education and public awareness programs.
In October of 1989, Florida’s Governor and Cabinet also directed the Florida Department of Environmental Protection to work with thirteen “key” manatee counties to implement measures for reducing manatee injuries and deaths. These counties include: Duval, Volusia, Citrus, Brevard, Indian River, St. Lucie, Martin, Palm Beach, Broward, Dade, Collier, Lee and Sarasota. Historically, most of the human-related manatee mortality has occurred in these counties. The first task of these 13 county governments, working with the state, was to develop site-specific boat speed zones for manatee protection. Their second task is to develop comprehensive manatee protection plans. Among other things, these manatee protection plans include a boat facility siting element, manatee sighting and mortality information, identification of land acquisition projects for manatee protection, law enforcement coordination, and an education and public awareness program.
The Florida Manatee Recovery Plan was developed as a requirement of the Endangered Species Act of 1973 (ESA). The recovery plan must present objective and measurable recovery criteria and site-specific management actions to minimize or remove threats to the Florida manatee. The U.S. Fish and Wildlife Service (FWS) must, to the maximum extent practicable, incorporate into each recovery plan objective measurable criteria which, when met, would result in a determination that the species be removed from the list of endangered and threatened species. In designating these criteria, the FWS must address the five statutory listing/recovery factors and measure whether threats to the species have been ameliorated or improved. The five listing recovery factors are:
- The present or threatened destruction, modification or curtailment of a species’ habitat or range.
- Overutilization for commercial, recreational, scientific or educational purposes.
- Disease or predation.
- The inadequacy of existing regulatory mechanisms.
- Other natural or man-made factors affecting its continued existence.
Propeller guards are a good idea to protect manatees, but only if they are used along with other protection measures, such as boat speed zones, enforcement, and habitat protection. Historically, people have equated propeller guards with being able to roll back speed zone protections for manatees. They have not understood that impact trauma from the boat’s hull or propeller (or propeller guard), called “blunt force trauma,” is often more deadly than the cuts from the propellers themselves. That’s why propeller guards are no substitution for slow and idle speed zones. While propeller guards could help minimize manatee injuries and deaths, they are not a stand-alone protection measure.
Manatees do not form permanent pair bonds like some animal species. During breeding, a single female, or cow, is usually followed by a group of a dozen or more males, or bulls, forming a mating herd. They appear to breed indiscriminately during this time. Although breeding and birth may occur at any time during the year, there appears to be a broad spring-summer calving peak.
Manatee calves are about three to four feet (one meter) long and weigh between 60 – 70 pounds (27-31 kilograms) at birth.
Newborn manatee calves are capable of swimming to the surface on their own and vocalize at or soon after birth.
In order to answer this question, we will need to discover and understand four key elements of a manatee’s reproductive biology.
- The age at which females reach sexual maturity and can successfully produce offspring.
Female manatees become sexually mature at about five years of age, but there has been evidence of manatees giving birth as early as three years old. - The length of time between birthing calves, also known as the calving interval.
Manatees most commonly have a calving interval of two to five years. The calving interval is influenced by a variety of factors, such as age, and therefore can greatly vary among individuals. A lower calving interval occurs when a female loses her newborn calf soon after birth. - The number of calves a female can give birth to at one time.
Usually, manatees only give birth to one calf at a time; it is possible for a manatee to give birth to twins, but this is rare. According to Mote Marine Laboratory, twins are born between 1.4 and 4 percent of the time for the Florida manatee. The gestation period for a manatee is about 13 months. - The lifespan of the female manatee.
The oldest a manatee can live to be is between 50 to 60 years old. Unfortunately, most manatees in the wild do not live past 30 years old.
Now for a little bit of math!*
On average, if a female manatee becomes sexually mature at 5 years old, has a calf every 3 years and never has twins, and lives to be 30 years old, she will have 8 to 9 calves in her lifetime.
A conservative estimate for a manatee that becomes sexually mature at 5 years old, has a calf every 5 years and never has twins, and lives to be 30 years old, would be that she would have 5 calves in her lifetime.
On the high end of the reproductive spectrum, if a female manatee becomes sexually mature at 3 years old, has a calf every 2 years, gives birth to one set of twins, and lives to be 30 years old, she may have up to 14 to 15 calves in her lifetime.
*These calculations do not include a death of a manatee calf soon after birth, which may result in a shorter calving interval. Nor do these calculations account for the fact that, unfortunately, many manatees do not live to reach age 30, or even to reproductive age, because of mortality from watercraft collisions and other human and natural causes.
There are several reasons why breeding manatees in captivity does not occur in Florida. First and foremost is that manatees naturally breed very well in the wild. Second, manatees born in rehabilitation facilities must overcome a steep learning curve in acclimating to life in the wild. When manatees are born in the wild, calves remain dependent on their mothers for up to two years while the mother teaches the calf necessary survival skills, such as migration routes, feeding spots, and warm water locations. Manatees born in captivity are at a great disadvantage in learning these survival skills. In addition, the space at rehabilitation facilities, where such breeding would take place, is limited and is needed to treat injured manatees. Finally, breeding manatees in captivity is also very expensive, would not improve species recovery, and would likely take valuable resources away from efforts to protect manatees in their natural environment.
While abandonment is believed to be possible for manatees, it is likely very rare and more likely that something happened to prevent the calf’s mother from continuing to care for the calf. On rare occasions, for example, orphaned calves who turn up in rehabilitation and later die are sometimes found to have birth defects, and it’s possible the mother knows the calf will not survive and leaves it. When the calf’s mother is unable to care for him or her (due to illness, injury, or death), other female manatees will sometimes nurse orphaned calves or calves of other mothers in addition to their own. Finally, manatee researchers also refer to “parking,” but that differs from abandonment. Parking is where a mother manatee leaves a calf in a safe spot, goes to feed, and then returns. Parking does happen with some frequency with manatees, so it’s important to monitor so-called “orphaned,” but otherwise healthy, calves for an extended period before rescuing to see whether the mother comes back for them.
Fossil remains of manatee ancestors show they have inhabited Florida for about 45 million years. Modern manatees have been in Florida for over one million years (probably with intermittent absences during the Ice Ages). The present Florida manatee (Trichechus manatus latirostris) is a subspecies endemic (or “native”) to Florida. Genetic studies indicate that it is not derived from the populations in Mexico or Central America but more likely colonized Florida from the Greater Antilles thousands of years ago, after the last Ice Age. Having inhabited these waters far longer than modern civilizations, manatees in Florida today have every right to be considered Florida natives.
There are two subspecies of the West Indian manatee: the Florida manatee and Antillean manatee. The main difference between them is simply their location. Florida manatees, as their name suggests, are typically found in the southeastern U.S., mostly around Florida. However, they have been known to travel further north and west, such as to the Carolinas and Alabama. Generally, these manatees do not travel south of Florida, but there have been a few cases of Florida manatees in places like the Bahamas and Cuba. Antillean manatees live in the Central America region, including parts of Mexico, the Caribbean, and the northern coast of South America. While there is little physical difference between the two subspecies, research has shown each subspecies has different DNA, showing that the two subspecies do not interbreed. This also allows researchers to identify a manatee’s original habitat. For example, if an Antillean manatee accidentally swims into Florida waters and gets injured, researchers would be able to tell it is an Antillean manatee based on DNA samples and would be able to release him back into Central American waters where he belongs.
The Florida and Belize manatee are considered two separate subspecies of the West Indian manatee (Trichechus manatus). The Florida manatee is part of the Florida subspecies (T. m. latirostris), found throughout the southeastern United States, while the Belize manatee is part of the Antillean subspecies (T. m. manatus), found in river and coastal habitats in Central and South America and the Caribbean. Subspecies are a geographical subunit that is genetically different from other populations of the species. The two West Indian subspecies have been designated by differences in skull measurements and genetic changes. Genetic studies, using highly informative microsatellite DNA, have shown that the Florida and Belize manatee populations are very different from one another and in fact do not travel or mix together (Hunter et al., 2010). Future genetic studies will look at Antillean manatee populations in other countries to find isolated populations that may be in need of further conservation actions. The related species of the West Indian manatee include the Amazonian manatee, the West African manatee and the more distantly related dugong (found in Australia, Asia, the Pacific Islands, and East Africa). Additionally, the Steller’s sea cow was found in the North Pacific and grew up to 30 feet long. Unfortunately, the Stellar’s sea cow was hunted to extinction within 27 years of its discovery in 1741.
Steller’s sea cow is named after the naturalist Georg Wilhelm Steller. Steller spent the winter of 1741 on Bering Island with other survivors of the wreck of the Russian ship, the “Saint Peter.” While there, he busied himself by collecting and recording detailed observations of the plants, animals, and minerals he found on the island. His notes, together with the studies of bones found on Bering and Copper Island, comprise the majority of information regarding the Steller’s sea cow. Sadly, Steller and his crew were also pretty much responsible for the extinction of the Steller’s sea cow. Because the animals were slow and stayed in relatively shallow water, they were easy to hunt for food. The survivors of the Saint Peter told stories of the sea cows on Bering Island after their return to Russia, and the Steller’s sea cow was hunted to extinction within 27 years of its discovery.
As far as we know, no manatee and dugong have ever been kept in captivity together. We don’t even know of dugongs in captivity in the U.S. or Europe. However, if a manatee and dugong were kept in captivity together, it is likely they would tolerate each other just fine. Male dugongs are a bit territorial, but even at that they could probably share a tank with manatees. In fact, even though they are not the same species, there is a possiblity that they could interbreed, which would not be a good idea. Their offspring would be sterile, or they would die before they reached sexual maturity.
Fossil remains of manatee ancestors show they have inhabited Florida for about 45 million years. Modern manatees have been in Florida for over one million years (probably with intermittent absences during the Ice Ages). The present Florida manatee (Trichechus manatus latirostris) is a subspecies endemic (or “native”) to Florida. Genetic studies indicate that it is not derived from the populations in Mexico or Central America but more likely colonized Florida from the Greater Antilles thousands of years ago, after the last Ice Age. Having inhabited these waters far longer than modern civilizations, manatees in Florida today have every right to be considered Florida natives.
We have to keep in mind that the adoptive manatees are wild animals with individual behavior. Some manatees come late and leave early and, occasionally, certain manatees will skip a season at Blue Spring or Tampa Electric and winter at another warm water area.
Since we have a limited number manatees in the Adopt-A-Manatee program, you will be one of many people who are an adoptive “parent” of the manatee you choose. However, the money from the Adopt-A-Manatee program goes toward increasing public awareness and education; sponsoring research, rescue, rehabilitation, and release efforts; advocating for strong protection measures, such as boat speed zones and sanctuaries; taking legal action when appropriate; and supporting rescue, rehabilitation, research, and education efforts in the Wider Caribbean, South America, and West Africa in order to protect all manatees and their aquatic habitat.
For more information on the manatee adoption program, visit the Adopt-A-Manatee® page.
The Florida Manatee Recovery Plan was developed as a result of the Endangered Species Act and is coordinated by the U.S. Fish & Wildlife Service (FWS).
In October of 1989, Florida’s Governor and Cabinet directed the state’s wildlife agency to work with 13 “key” manatee counties in Florida to reduce injuries and deaths. These 13 counties were: Brevard, Broward, Citrus, Collier, Dade, Duval, Indian River, Lee, Martin, Palm Beach, St. Lucie, Sarasota, and Volusia. Over the years, these 13 county governments have worked with the state to develop site-specific boat speed zones to reduce the likelihood of watercraft collisions and to implement comprehensive manatee protection plans (MPP) for each county.
A manatee zone warning sign in Tampa Bay.
Other conservation measures deemed important to saving manatees include: research addressing biology, mortality, population and distribution, behavior, and habitat of manatees; implementation of management plans; posting of regulatory speed signs and levying of fines for excess speeds in designated areas; manatee education and public awareness programs; and public acquisition of critical habitat and creation of sanctuaries.
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