Manatee
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 Manatee with calf.
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Trichechus inunguis |
Manatees (family Trichechidae, genus Trichechus) are large aquatic mammals sometimes known as sea cows. The name comes from the Spanish manatí, which itself comes from a Carib word meaning "breast."
The Trichechidae differ from the Dugongidae in the shape of the skull and the shape of the tail. Dugongs have a forked tail, similar in shape to a whale's, while manatees' tails are paddle-shaped. They are herbivores, spending most of their time grazing in shallow waters, and can weigh anywhere from 500 to 1000 kg. When born baby manatees have an average mass of 30 kg.[1]
Manatees inhabit the shallow, marshy coastal areas and rivers of the Caribbean Sea and the Gulf of Mexico (T. manatus, West Indian manatee), the Amazon basin (T. inunguis, Amazonian manatee), and West Africa (T. senegalensis, African manatee). They spend half of their day sleeping in the water, surfacing for air regularly, and at intervals of not longer than 20 minutes.
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[edit] Vulnerability
All three species of manatee are listed by the IUCN as Vulnerable to extinction. Although manatees have no natural predators, human expansion has reduced their natural habitat in the coastal marsh areas and many manatees are injured or killed by collisions with powerboats. Manatees occasionally ingest fishing gear (hooks, metal weights, etc.) while feeding. These foreign materials do not seem to harm manatees, except for monofilament line or string. This can get clogged in the animal's digestive system and slowly kill the animal. Manatees can also be crushed in water control structures (navigation locks, flood gates, etc.), drown in pipes and culverts, and are occasionally killed from entanglement in fishing gear, primarily crab pot float lines. Manatees are also vulnerable to red tides, blooms of algae which leach oxygen from the water.
Manatees were commonly hunted for their meat by natives of the Caribbean, although this is much less common today.[2]
On June 8, 2006, The Florida Fish and Wildlife Conservation Commission voted to reclassify the manatee on Florida's list, to a "threatened" status in that state.[3] While none of the state laws protecting manatees have changed, many wildlife conservationists are not pleased with the removal decision.[4] Manatees remain classified as "endangered" at the federal level.
The population of manatees in Florida is thought to be between 2000 and 3000.
[edit] Habitat
Manatees typically inhabit warm, shallow, coastal estuarine waters. Manatees often congregate near power plants, which warm the waters. Some have become reliant on this source of unnatural heat and have ceased migrating to warmer waters. Some power plants have recently been closing and the U.S. Fish and Wildlife Service is trying to find a new way to heat the water for these manatees.
The main water treatment plant in Guyana has four manatees that keep storage canals clear of weeds.
The natural source for warm waters for manatees during the winter is spring fed rivers. The West Indian Manatee migrates into Florida rivers such as the Crystal River, The Homosassa River and The Chassawohitzka River. The head springs of these rivers maintain a water temperature of 72 degrees year round. During the winter months, November to March, approximately 400 West Indian Manatees (According to the National Wildlife Refuge Service) congregate in the rivers in Citrus County, Florida.
Manatees have been spotted as far north as Cape Cod, and as recently as the late summer of 2006, one made it up to New York City and Rhode Island's Narragansett Bay, as cited by the Boston Globe. According to Memphis, Tennessee's Commercial Appeal newspaper, one solitary manatee was spotted in the Wolf River harbor near the Mississippi River in downtown Memphis, Tennessee, on October 23, 2006.
[edit] Disposition
Manatees are slow moving, non-aggressive, and generally curious creatures. They enjoy warmer waters and are known to congregate in shallow waters, [1] and frequently migrate through brackish water estuaries to fresh water springs. Their slow moving, curious nature, coupled with dense coastal development, has led to a number of harmful interactions with boat propellers. As a result, a large portion of manatees exhibit propeller scars on their backs. Often the cuts lead to infections which can prove fatal. Internal injuries stemming from hull impacts have also been fatal.
[edit] Diet
Manatees are herbivores and eat over 60 different plant species such as mangrove leaves, turtle grass, and types of algae, using their divided upper lip. An adult manatee will commonly eat up to 9% of its body weight (approx 50kg) per day. Antillean manatees have been known to eat fish from nets.
[edit] Captivity
The currently oldest manatee in captivity is Snooty who is held at the South Florida Museum. He was born at the Miami Seaquarium on July 21, 1948 and came to the South Florida Museum in Bradenton, Florida in 1949, where he still lives.
[edit] Manatee hunting
Manatees were traditionally hunted by indigenous Caribbean people. When Christopher Columbus arrived in the region, manatee hunting was an established trade. Native Americans hunted manatees to make war shields, canoes, and shoes, though the manatee was predominately hunted for its abundant meat. Roman Catholic settlers in the area classified the manatee as a fish, since it lived in water, which made it suitable for Friday meals when eating meat was prohibited. Manatees were also hunted for their valuable bones, which were used to make "Special Potions." Up until the 1800s, museums paid as much as $100 for manatee bones or hides. Though hunting manatees was banned in 1893, illegal poaching of the animals continues to the present day.
[edit] Cultural references
- It is thought that sailors created the myth of the mermaid after mistaking manatees for half-fish, half-human creatures.
- Manatees' popularity is steadily growing, as is shown by references to them in popular shows such as South Park, The Simpsons, Family Guy, O'Brien, the popular webcomic Questionable Content and the appearance of many non-profit organizations which benefit manatees.
[edit] References
- Shoshani, Jeheskel (November 16, 2005). Wilson, D. E., and Reeder, D. M. (eds): Mammal Species of the World, 3rd edition, Johns Hopkins University Press, 93. ISBN 0-801-88221-4.
- ^ http://www.saj.usace.army.mil/permit/hot_topics/SFLAEIS/PDF_Files/wima.pdf
- ^ http://www.ambergriscaye.com/25years/huntingformanatees.html
- ^ http://www.myfwc.com/manatee
- ^ http://www.cnn.com/2006/TECH/science/06/08/florida.manatee.reut/index.html
[edit] External links
- http://www.homesafe.com/manatee/index.html A website with many manatee photos, real-life manatee encounters and a manatee rescue in Homosassa, Florida
- http://bagheera.com/inthewild/van_anim_manatee.htm Bagheera] An educational website of Earth's endangered animals
- http://cars.er.usgs.gov/pics/manatee/manatee.html USGS gallery on manatees, also depicting habitats close to power plants
- http://www.savethemanatee.org A website dedicated to helping save the manatee.
