Manatee Faq
01-29-2003, 04:59 PM
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CYMFC3S's Manatee FAQ
Anatomy and Physiology
Q. Do manatees have good eyesight?
A. Surprisingly enough, manatees have fairly good visual acuity and can distinguish between different-sized objects, different colors, and patterns. Their eyes are small, and they have a nictitating membrane that can be drawn across the eyeball for protection.
Q. How do manatees communicate with each other,
and do they hear very well?
A. 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.
Q. What is the “peduncle” of a manatee?
A. The peduncle is the base of the tail, right where it connects to the body of the manatee.
Q. What is the average weight of a manatee?
A. The average adult manatee is about 10-12 feet long and weighs about 1,500-1,800 pounds.
Q. What is the record weight of a manatee?
A. Adult manatees have been known to exceed lengths of 13 feet and weigh over 3,500 pounds.
Q. What is the record age of a manatee?
A. Scientists believe that manatees are capable of living for 60 years or more. One manatee living in captivity, Snooty, is now over 50 years old. We know how old he is because he was born in captivity in 1948. Unless you know when a manatee is born, the only way to determine their age is by counting growth layer rings in their ear bones. Obviously this can only happen after a manatee has died.
Q. How can you tell a female from a male manatee?
A. If you look at the underside of a manatee, referencing from the head to the tail, the genital opening in the male manatee is just below the umbilicus (belly button), and the female's genital opening is just above the anus. That's how you can tell a female from a male.
Q. Do manatees have teeth?
A. They do, and one of the interesting things about manatees is that they have what is known as "marching molars." In fact, molars are the only type of teeth that manatees have. Their teeth are also unique because they are constantly replaced. They form at the back of the jaw, wear down as they move forward, and eventually fall out! Tooth replacement is an adaptation to the manatee's diet of abrasive plants that are often mixed with sand.
Q. How do people tell manatees apart?
A. 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.
Q. What are the kinds and sizes of manatee boat scars? Are any scars curable, or do they stay on the manatees forever?
A. 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.
Q. Does a manatee's skin ever change color?
A. 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.
Q. What is the “green stuff” you see on their bodies?
A. 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!
Q. What is the purpose of a manatee's whiskers?
A. Although the exact purpose is not clear, it is thought the “vibrisae” or whiskers on a manatee’s snout are sensory in function. Researchers have discovered that each whisker has a nerve connection to a small cluster of cells in the manatee’s brain devoted exclusively to that whisker! Further research may solve more of these mysteries.
Q. Do manatees have blowholes?
Manatees do not have blowholes. They breathe through nostrils, like seals. Their nostrils have fleshy "valves" that close when they are underwater
Q. Why can't manatees adapt well to cold water?
A. 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.
Behavior
Q. What time of year do manatees migrate?
A. In the winter, usually November through March, manatees are concentrated primarily in Florida. Manatees are susceptible to cold-related disease and, in the winter, gather near warm water sources such as natural springs or warm water effluents of power plants. Water temperatures below 68 degrees usually cause manatees to move into these warm water refuge areas. 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 Lousiana and as far north as Virginia and the Carolinas.
Q. How long does it take for the manatees to get to their destination?
A. It depends on where they are going. Manatees are slow-moving animals. It is estimated that manatees can travel up to 20 mph in short bursts, but they usually travel between 3-5 mph.
Q. How far can manatees swim in a day?
A. It depends on the individual manatee. Just like humans, some manatees are more predisposed to traveling than others. Some manatees are being tracked using a satellite transmitter. As a result, researchers have been able to record some interesting manatee movements. One manatee made a 150-mile trip in less than four days on one occasion. She swam nearly 45 miles per day!
Q. How do they get prepared for the long journey?
A. 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.
Q. How deep can manatees go in the water?
A. Manatees prefer waters that are three to seven feet deep. Manatees are found in both salt and fresh water. Along the coast, manatees tend to travel in water that is 10-16 feet deep, and they are rarely seen in areas over 20 feet deep.
Q. How can manatees go such a long period of time without taking a breath?
A. Manatees, like other aquatic mammals, do most of their feeding underwater and must be able to hold their breath long enough to feed efficiently. 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. 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 extend the length of the body cavity and so are oriented in the same horizontal plane as a manatee. 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-diaphrams.” Scientists do not know whether these cavities can function independently, but we do know that manatees can have severe infections in one lung even though the other seems to function normally. Besides breathing, the lungs help the manatee with buoyancy control. Intervals between breaths are prolonged by replacing a large percentage of the air in the lungs with each breath. 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% of the air in the lungs in a single breath.
Q. What do manatees do during a hurricane?
A. Researchers believe that manatees are well adapted to the aquatic environment and often seek sheltered waters during rough conditions.
Q. Why are manatees attracted to the sound of motors?
A. They aren't. Research has shown that they actually avoid them, when they can.
Q. Is it possible to teach manatees to do tricks?
If yes, what tricks can they perform?
A. Manatees are definitely smart enough to train. Manatees 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!
Food
Q. What do the manatees eat?
A. Manatees are herbivores (plant-eaters), feeding on a large variety of submerged, emergent, and floating plants. Seagrass beds are important feeding sites for manatees. Some favorite foods of manatees include: Marine vegetation: Manatee grass, turtle grass, shoal grass, widgeon grass. Freshwater vegetation: Hydrilla, eelgrass, water hyacinth, and water lettuce.
Q. Do manatees ever eat plankton or small fish?
A. 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.
Q. How much does a manatee eat in one day?
A. It is estimated that a manatee can eat about 10-15% of their body weight in vegetation daily. So a 1,000 pound manatee would eat between 100-150 pounds of food a day!
Q. Where are manatees found in the food chain?
A. 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.
Q. If manatees are herbivores, why do they weigh so much?
A. 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.
Breeding and Reproduction
Q. What is the manatee's gestation period?
A. The gestation period is approximately 13 months.
Q. How much do manatee calves weigh when they are born? Do they stay with their families for a long time?
A. Manatee calves are about three to four feet long and weigh between 60 and 70 pounds at birth. Mother manatees nurse their young for a long period, and a calf may remain dependent on its mother for up to two years. The female manatee assumes total responsibility for raising the calf. The calf nurses from nipples located behind the mother's flippers and begins to eat plants a few weeks after birth.
Q. How do manatees produce calves?
A. Manatees do not form permanent pair bonds like some animal species. During breeding, a single female is usually followed by a group of a dozen or more males, forming a mating herd. 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 -- twins are rare. Intervals between births range from two to five years. Scientists believe females do not become sexually mature until five years of age. Males are mature at approximately nine years of age.
Population
Q. How many manatees are there, and how are they counted?
A. For years now, researchers have believed that the manatee population was somewhere between 2,000 and 3,000 animals. The last aerial survey of the Florida manatee population was done in March 2002. The survey showed a count of 1,796 manatees. A synoptic survey is a statewide aerial survey designed to get a head count of individual manatees. The success of synoptic 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 "nose" count. Synoptic surveys are not the most reliable way to determine overall manatee population because so much depends on weather conditions, but they are the only available method at present.
Q. How many manatees are there left in the world?
A. 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 considered endangered.
Q. In terms of evolution, how long have manatees been around?
A. Actual manatee fossils found all over the world go back as far as 60 million years. Modern manatees evolved from four-footed land mammals. Manatee fossils found in Florida’s springs date back about 45 million years.
Manatee Mortality
Q. Do manatees have any predators?
A. No. Manatees have no predators.
Q. Were manatees ever hunted for food?
A. Florida was established as a manatee sanctuary as early as the eighteenth century. 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 U.S., 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 U.S. is extremely rare, but it still occurs.
Q. Are manatees ever attacked by sharks?
A. Manatees are not usually hunted by sharks because they generally don’t share the same habitat. Larger-sized sharks are generally found offshore in deeper waters. The smaller shark species that may inhabit lagoons and shallower waters probably would not attack manatees because they are too big. Alligators do not usually attack manatees for the same reason.
Q. What are the different types of speedboats that are dangerous to the manatees?
A. All types of boats that are going too fast are dangerous to manatees. Most manatees only travel about 3-5 mph hour (they can go up to 20 mph in short bursts), so any boat that is traveling faster than 15-20 mph is capable of injuring or killing a manatee.
Q. Have scientists decided what killed so many manatees in 1996? Can anything be done to prevent these mortalities from happening again?
A. A single catastrophic event in 1996 was responsible for 151 manatee deaths. These manatee deaths were attributed to red tide, a term used for the proliferation or "blooms" of tiny marine organisms called dinoflagellates. The organism's pigments can cause the water to appear red, green, or yellow. Microscopic, but found in great abundance, they give off a toxic byproduct that affects the central nervous system of creatures in the area of the bloom. The red tide epizootic began on March 5 and continued through April 28 along Florida's southwest coast, wiping out approximately 15% of the known west coast population of manatees.
In 1982, another outbreak of red tide was believed to have contributed to the death of 37 manatees. Over the years however, red tide manatee mortality events have been rare. Red tide is considered to be a natural event and therefore may not be preventable. But scientists are currently looking at possibilities to reduce the risk to manatees during red tides. Monitoring and prediction of red tide distribution has been deemed crucial. The possibility of reducing water salinity in certain areas is also being investigated as red tide requires high salinity water to survive and does not do well in water less than 2.5% salt like brackish or river water.
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