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Manatee

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Manatee
Manatee and baby.jpg
Scientific Classification
Genera and Species
Image of Trichechus manatus.jpg
Manatee having a snack

Manatees are any of the species belonging to the taxonomic family Trichechidae. They are best known for their round, large, clumsy looking appearance, and for being the only marine mammal left that eats solely a vegetarian diet. It is also thought to be the source of the legend of mermaids[2].

Body Design

Skeleton of a manatee

The Manatees and Dugongs have an aerodynamic body to help them glide through the water.[3] They have two frontal fins that form paddle like flippers with four extending nails. [4] These flippers allow them to steer themselves through the water. To propel themselves through the water, manatees have powerful tails [5] that are flattened with a singular lobe. [3] The manatee has an arched head and a blockish muzzle. [3] Their heads are covered with wrinkled skin, and overlaid with bristles. [4] Manatees have a dense skeleton from the base of the skull downwards, particularly their ribcage. [3] Unlike most mammals, which have seven vertebrae, manatees only have six. Because of this, they are unable to turn their heads, and in order to see behind them, they need to turn themselves completely around. [6]

A manatees mouth has two lips that are extremely divided to the right and the left, [3] each half able to move independently. [6] Covered with rough whiskers on the outside, these lips work together to grab plants. [3] The only teeth that manatees have are molars, which are constantly being replaced. [6] Manatees have small eyes, though they are able to see quite well, despite murky waters. [5] They possess a membrane able to be pulled over their eyes for defense against the mud and sand floating around them. They also have fairly good hearing, even though they have no outer ears, on account of their big inner ear structure. [6] Manatees have a grey-brown coloring and quite thick wrinkled skin, that algae tends to grow on. [5] Manatees can grow up to thirteen feet and have weighed in at 1,300 pounds. However, they possess very little body fat, even though their size would suggest otherwise. [6]

Life Cycle

Mother Manatee (Trichechus inunguis) swimming alongside her young calf.

The manatees have no specific mating season, [5] but their gestation period lasts for about 12 months. [4] A female manatee will give birth to one calf at a time, weighing in at about 60-70 pounds and measuring around 3-4 feet. [5] Immediately after giving birth, the mother must take the calf to the surface of the water so they can take a breath, however, the calf will be swimming on its own within an hour of birth. [6] The calf nurses underwater [5] for around two years. During this time the calf is completely dependent on its mother. The calf will not become sexually mature until it is five years old. The reproduction rate in manatees is considered very low, and only one calf is born every 2-5 years. [4]

An average manatee can live to be 60 years old. [6] They spend most of their time swimming, eating and lying around. [4] They tend to live in groups, albeit loose ones, sometimes alone, sometimes with over one hundred. The groups congregate around sources of warm water, like stream power plant outflows. When they are in their groups, manatees are constantly touching each other, rolling on top of and bumping against each other. [3] Manatees die from natural causes such as cold stress, when the water drops below 60 fº, diseases and pneumonia, but human-related deaths are a common occurrence as well. Boat collisions, drowning in canal locks, eating fishing hooks and litter and becoming entangled in fishing lines are the most common fatalities when humans are involved. [4]

Ecology

Map of specimen collection for specimen Trichecidae

Manatees are nomadic creatures, migrating on a yearly basis. In winter, manatees living in the U.S. are located generally in Florida, while in the summer they head West towards Texas and North towards Massachusetts. However, during the summer months they are most often seen in South Carolina, Alabama and Georgia. Manatees can also be in Central and South America. Their habitats consist of estuaries, saltwater bays, canals and shallow, slow-moving waters. They especially prefer the locations abundant in their food source. [4] Manatees are solely marine mammals, never coming onto land, but must swim to the surface of the water in order to breathe. While swimming or exerting energy, they must go up for breath every three or four minutes, [6] but when resting, they are able to remain underneath the water for up to twenty minutes. The manatee has no natural enemies[4], although they sometimes startle a crocodile, they are only really hunted by humans[6].

A manatee’s diet consists completely of submerged and floating plant life[4] which they consume by grazing. [5] These herbivorous animals are able to consume anywhere from 10-15% of their body weight[4], easily over 100 pounds[6], daily in plant life. However, a small fish or two will occasionally be caught up in a manatee’s vegetarian meal.[4] Manatees eat regularly and rest frequently. To communicate, manatees send out a wide range of noises, usually between a mother and her calf, but also to maintain contact[6], and to express fear or excitement. [5] Manatees, despite their clumsy appearance, [6] and the slow, relaxed movements that they are commonly known for, are quite agile swimmers. A manatee is very good at underwater acrobatics, performing somersaults, barrel-rolling and body surfing while playing with other manatees.[5] Although they can generally only swim an average of four miles an hour, a manatee can swim up to twenty miles per hour for a short amount of time.[4]

An Endangered Species

The manatee (Trichechus manatus) is now considered an endangered species.

The manatees’ conservation status is considered vulnerable and they are federally listed as an endangered species in the United States. The estimated number of mature adults is under 10,000, with less than 2,500 in the United States. These numbers are projected to decrease another 10% in the next three generations. [6] In times past, manatees were hunted for their fat, meat and tough skin[2], and even today are still hunted in some places for their meat. [3] Manatees are quite vulnerable to human interference, like boat collisions, now considered the greatest threat to manatees. [2] In 2010, eighty three manatees died as a result of boating collisions in Florida alone. [7]

One of the main threats to Manatees is boating collisions. Being surface-dwelling creatures in shallow water[2], they have very little time or ability to dodge approaching boats. In almost all cases of a collision, the manatee will die from the injuries, and the few that survive will bear scars for the rest of their lives. Another danger to manatees is becoming entangled in fishing lines. The main reason this happens is because as they graze, their heads are down, so hooks and fishing lines can be ingested or caught on their tails. Being tangled in fishing lines can lead to infection, long-term injuries and even death. Often times manatees can find themselves caught in ropes with buoys on the surface, which can be very heavy with the weights connected to them. The manatees often end up drowning from this particular snare, but any that survive will have to drag all the weight for miles before dying from infection from any injury sustained from the heavy ropes. [7] Another danger is habitat destruction, killing off the seagrass estuaries where the manatees feed and live. [2] Development along the coastline in the southeastern U.S. has reduced manatee habitat, taking away marine vegetation and sea grass beds. [7] Chemical pollution has also harmed their habitat, reducing their immunity and making them more vulnerable to infection.[2]

It is illegal to harass, hunt, capture or kill any marine mammal manatees in the U.S. under federal law because of the Marine Mammal Protection Act of 1972, and the Endangered Species Act of 1973. They are further protected under the Florida Manatee Sanctuary Act of 1978. [4] Even back in the 1700’s, England had laws prohibiting manatee hunting[2], and today, breaking any of those federal laws can be answered with convictions coupled with fines or imprisonment. Florida produced the Florida Manatee Recovery Plan to save manatees from their spot on the endangered species list. They developed several “tasks” in order to achieve this goal. These included site-specific boat speed zones, research of mortality and behavior, management plans and several others[4]. Tourism has also assisted with local conservation steps. Since tourists are drawn to manatee-watching opportunities, locals take greater care in preserving the habitats to keep tourists coming in and spending money.[2]

Video

This manatee seems to think that this man's glove is a plant. The two separate upper lips are displayed here showing off the ability to move them separately and use them to pull in their meal.

Gallery

References

  1. Trichechidae Wikispecies. Web. Last Updated February 22 2012.
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 Author Unknown http://www.bagheera.com/inthewild/van_anim_manatee.htm FLORIDA (WEST INDIAN) MANATEE AN ENDANGERED SPECIES] Bagheera. Web. Accessed April 3, 2014.
  3. 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 Myers, Phil. Trichechidae AnimalDiversityWeb. Web. Accessed March 22, 2014.
  4. 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 4.13 Unknown Author Manatee Facts SavetTheManateeClub. Web. Accessed March 22, 2014.
  5. 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 Unknown Author Florida Manatee DefenderOfWildlife. Web. Accessed March 22, 2014
  6. 6.00 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.10 6.11 6.12 Gammon, Katharine. Fun Facts About Manatees LiveScience. Web. Published February 25, 2013
  7. 7.0 7.1 7.2 Deedy, Jenna Why is the Florida Manatee Endangered? thewinterdolphinchronicles. Web. Published December 11, 2011.