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.
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 adapted to hear infrasound, frequencies too low to be heard by the human ear, generally less than 20 hertz.
A. The peduncle is the base of the tail, right
where it connects to the body of the manatee.
A. The average adult manatee is about 10-12
feet long and weighs about 1,500-1,800 pounds.
A. Adult manatees have been known to exceed
lengths of 13 feet and weigh over 3,500 pounds.
A. Scientists believe that manatees are capable
of living for 60 years or more. One manatee living in captivity is now
about 50 years old.
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.
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.
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.
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.
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.
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!
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.
Manatees do not have blowholes. They breathe
through nostrils, like seals. Their nostrils have fleshy "valves" that
close when they are underwater
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.
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.
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.
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!
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.
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.
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.
A. Researchers believe that manatees are well
adapted to the aquatic environment and often seek sheltered waters during
rough conditions.
A. They aren't. Research has shown that they
actually avoid them, when they can.
A. Manatees are definitely smart enough to
learn tricks. 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!
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.
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.
A. It is estimated that manatees 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!
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.
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.
A. The gestation period is approximately one
year.
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.
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.
A. The last aerial survey of the Florida manatee
population was done in February of 1998. The survey showed a population
count of 2,019 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.
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.
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.
A. Manatees were hunted for food in the U.S.
until around 1950. Until the Endangered Species Act in 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 they use it for food.
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.
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.
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.
A. Save the Manatee Club is in favor of prop
guards, and there are a number of manufacturers of them in Florida. However,
most manatee deaths caused by watercraft collisions are from the actual
impact of the boat’s hull striking the manatee rather than from propeller
injuries. Therefore, although we support prop guards, we don't want people
to think they are a "cure-all" to the problem. Because manatees generally
travel about 3-5 miles per hour and can travel up to only 20 mph in short
bursts, Save the Manatee Club supports slow speed zones in areas where
manatee travel has been documented. However, on large vessels such as tug
boats and freighters, propeller guards would certainly decrease the likelihood
of manatee mortality. These types of boats are already going slow, but
the props are so large that manatees can get pulled in and chopped up.
Prop guards would help decrease manatee mortality in these cases.
A. The name manatee comes from the Haitian
word “manati.” The scientific genus name Trichechus is Latin for hair.
A. "Sea cow" is a common term for manatees
and dugongs. This name likely comes from the fact that manatees are herbivores
(plant-eaters), as are cows.
A. 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 and were wiped out that
same year.
A. 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.