Tara and Scott SCUBA along the Wall at Runway Ten, 15 m deep, San Salvador, Bahamas.
The number of Manatees in the world is not known but records show a decline in the last century. The Florida manatee numbers in Florida is thought to be around 2500-3000 individuals. Other populations of this great mammal worldwide are not known. Estimates are that the current population could go down by as much as 45-50% by the year 2050. Much of the rapid decline in the last 50 years has been attributed to human influences, natural causes such as climate and disease have taken there toll on the manatees too. A great deal has been done to try and arrest the situation and hopefully save this giant from extinction in the near future. The more people are aware of the manatees and its status the higher the chances of survival of the manatees worldwide.
Working as a naturalist in Kenya, the Florida Manatee Trichechus manatus latirostris, seemed to always rival the Florida Panther and the Everglades whenever I got to enquire about Florida and its environment. In 2001 I got to visit an aquarium in Sarasota and found myself staring at live manatees for the first time.
Averaging 10-13 ft in length, manatees live mainly in the sea just like dolphins, seals and whales which are other aquatic mammals. Preferring water depths of 4-10ft and rarely in water over 20ft deep manatees are also to be found in coastal bays, inlets, springs, salt marshes, canals and even in undammmed rivers. This is rather unusual considering that they weigh averages of over 1000lbs with some bulls weighing in at 3500lbs.
Adapted to living in water, manatees can stay under water for 20 minutes if need be but just like other mammals fresh breaths of oxygen are needed hence the manatees will surface for air every 3-5 minutes.
Manatees belong to a group of mammals called Sirenia named after the sea nymphs in ancient Greek myths. Fossil records of manatees date back to 60million years ago; however the fossil remains in Florida are dated back to 40 million years ago. Modern manatees evolved from four-footed land mammals. The idea that they were closely related to elephants really got me interested in learning more about the manatees.
In the wild manatees are found in the tropics and sub-tropics. This is because they prefer water that is generally above 700F. Rarely do you find manatees in waters below 60oF. The temperature of the water is essential to the manatees because of their slow metabolism. Thus they are unable to metabolize energy quick enough to stay warm in water that dips below 68oF.
Manatees have a long lifespan of 60-70 years. Males are generally solitary unless during courtship when 10 or more males can meet around a female in estrus. Another period of congregation is during migration in search of food or when they escape the cold waters during the winter months. Young males form bachelor herds. The main social bonding is normally between mother and calf as the calves stay with the mother for close to two years.
Other Manatee facts:
Though adapted to living under water manatees have 5 senses same as humans: their eyes have a membrane that covers the eyes almost like protective goggles. However their eyesight is generally regarded as poor and estimates have it that they cannot see beyond 115ft. Hearing is excellent with their small external slits. They communicate underwater in sounds that are audible to the human ear; smell is through combined chemical glands that enable them to identify other manatees and also taste food; touch is through whiskers called vibrissae which are all over their bodies and are sensitive to the touch. They use these whiskers as feelers.
Manatees feed on water hyacinth, sea-grass, algae, and crustaceans such as barnacles growing on these plants.
With no front teeth, manatees have adapted to having special “marching molars”. They have 4 set of 6-8 molars just like elephants that replace each other as a set wears out.
They also have a large spilt upper lip of which the left and right sides can move independently to move the food into place; ridged pads behind the lips break food down into smaller pieces before the molars grind it up.
When manatees congregate there are social interactions such as mouthing, body-surfing, somersaulting, barrel- rolling, upside down gliding etc.
Races of Sirenians in the World.
The Sirenian order includes: the West Indies Manatee Trichechus manatus of which the Florida Manatee is a subspecies that ranges from southeastern US to northern Brazil; the West African Manatee Trichechus senegalensis, found in the coastal waterways on western African nations such as Nigeria and Cameroon; and the Amazonian manatee Trichechus inunguis, which lives in the fresh waters of the Amazon River and its tributaries.
The other relative to the manatee in the water is the Dugong Dugong dugong, found in the coastal waters of the Indian and Pacific oceans. The dugong differs from the manatee in that it only has 2 sets of teeth.
The Stellar’s sea cow Hydrodamalis gigas was also in this group but was hunted to extinction within 27 years of its discovery in 1741. At one time it was found in the cold waters of the Bering Sea. The largest Sirenian on record grew to be about 4.4 tons!
Status of the Florida Manatee,
The manatee is endangered at both the state and federal levels in the US. Controversy surrounds the status of the manatee worldwide since the official numbers of the rest of the species are not known worldwide. Only Florida has an estimate of the animals left in the world.
A recent aerial census done in February 2004 got the number of manatees at 2568 animals (www.savethemanatee.org). Out of Florida the status of the manatee (West Indies Manatee) is unknown.
Estimates of manatees in Panama have only about 100 animals left in the wild. The situation is grim of the West African Manatee as well.
Problems that the Manatees face.
Collision with recreational boats, barges and ships is the number one killer of manatees that is human induced. Being that the manatees are found in shallow water, most of the time this is where the boats would start at. The injuries sustained from the rotor blades, scar the manatees and do end up fatal in some cases. Some manatees have been identified to have rotor scars from as many as 16 different boats (Gerstein).
Though manatees have acute hearing, Research has shown that when the boats slow down in manatee watch areas, sometimes it does not really help. This is because the rotating propeller generates low-frequency sounds which are impossible to locate and indistinguishable from the ambient noise until it is dangerously close to the manatee. Manatees are passive listeners restricted to auditory landscape unlike echolocation by dolphins which can use sonar navigation to detect objects in the environment (Gerstein).
They need to see the objects to flee away from. With Florida boat registrations soaring, manatee deaths hit a record high of 95 in 2002 (Florida Manatee Mandate). With speeds of about 2-6 miles an hour normally this is not enough to get out of harms way. Even the highest recorded speeds of 15m/hr are normally not quick enough.
The exponential human population growth over the last couple of decades has spelled doom for the manatees as this has meant dwindling habitats. Much of their habitat has been lost to recreation and human habitat in the warm coastal waters (Earthwatch Institute Journal; Jan 2004, Vol.23 Issue 1, pg 57). In addition dams lead to heavy silting which is also another cause of manatee habitat loss. Susceptible to cold water the competition with humans is a losing battle as more and more warm coastal land is lost to development. This leads to disease like pneumonia which the manatees are highly susceptible to. The few sanctuaries that have been created in Florida and other places are not enough to sustain them.
Toxins from algae especially directly related to the “red-tides” have also led to fatalities of manatees. It has been confirmed that more than 150 deaths of Florida Manatees in 1996 were as a result of algal toxins produced by G .breve (Han et-al, 2003). Estimates suggested that about 10% of the total population has been wiped out by the toxins which were suggested to have entered through the food web as well as from direct contact when with toxic aerosols when the animals broke the surface to breath. The algae toxins were derived from red-tide. In 2003 sixty deaths of manatees were attributed to red tides (New York Times, 2003).
Manatees have a highly developed immune system believed to play an important role in protection against the harsh marine environment and possibly natural disease. However the papilloma virus has been identified to weaken this immune system. This results in microscopic lesions indicative of papilllomatosis that leads to mucosal tumors (McClinktok, 2004).
The viruses and other bacteria spread quickly especially when the manatees are forced into close quarters as happens in the electric power plants that manatees are known to congregate in when they seek warm water during the winter months e.g. in Florida.
Sea-grass which is main food source of the manatees does face their own problems of overharvesting, pollution and also being dragged off in destructive fishing practices (Davidson, 1998). Manatees need to eat a lot to keep the heavy body mass and also to generate energy and stay healthy. Manatees need to eat roughly about 11% of their body weight, spending about 6-8 hours a day grazing. This means anywhere between 80-380ls required each day. The effects on the sea-grass thus do have a direct influence on the number of manatees (Burke, 2004).
Manatees also drown when they are trapped in canals, gill nets. Floodgates also crush them when they are unable to swim by fast enough as this is not a natural danger that they have come to associate with.
In other countries where there are no concrete plans laid down for conservation of manatees there is still illegal poaching of the manatee for its meat and thick skin. This has been recorded in countries such as Panama and Colombia. The West African manatee of which little research is known about has also suffered the same fate in addition to damming, and drowning in fishermen’s nets.
Abrupt climatic changes that lower the temperature to less than 60oF also do pose a threat to the manatee populations worldwide. This is because as mentioned earlier the manatees are susceptible to pneumonia.
What does the future hold for the Manatees?
The status of the Florida manatee Trichechus manantus latirostis seems to be stabilizing in Florida (Christian, 2003).
Sanctuaries are being created for the manatees; this has been the case in Florida. Other countries that are trying to conserve their manatees are Belize where ecotourism has picked up and the local guides seem to realize that the conservation of the manatees promotes tourism and all the positive benefits that come with tourism such as job creation.
However the Bush administration is facing criticism for not doing enough to create more sanctuaries needed for the manatees.
Non governmental organizations and other private organizations have come up and helping to promote the awareness of the status of the manatee. Education to fishermen and other boat users is also a great way to promote the sustainability in the manatee populations. Greater awareness especially in the field is key to the survival of the manatees (Aipanjyguli, et-al 2003).
Though still not widespread there is the hope that boats can be fitted with an acoustic alerting device that is audible to the manatees and give the animals the opportunity to save themselves (Gernstein). This involves bow mounted parametric transducer that creates a stable directional beam of sound just under the surface of the water for up to 200 meters.
In conclusion even though the Florida manatee numbers seem to be stabilizing, situations in other regions of the world where the manatees range are grim. In addition the manatees do migrate in response to the water temperatures and food. This would therefore put them in danger in areas where they are still hunted and also where the fishing practices are not regulated.
The sanctuaries do provide a temporary home and is vital to education of fishermen and the general population. The more people know about the endangered status of the manatee worldwide the better the chances of survival of the manatees.
I believe that the suggestion of equipping boats with acoustic alerting devices to be used in shallow waters and manatee sanctuaries is crucial to avoiding the rotor blades accidents. The sound from these acoustic devices is audible to the manatees close to the surface and thus gives them a chance to save themselves before it is too late!
Creation of more sanctuaries worldwide and limiting the harassment of manatees by fishermen and snorkelers is also one way that may help with a sustainable future for the manatees.
It is also crucial that the status of the other manatees in other countries be ascertained as soon as possible to try and prioritize conservation efforts. This is because of the migratory nature of the manatees. "Without proper habitat, manatees will be doomed to live out their lives in zoos." (Florida Manatee Mandate).
Aipanjyguli, S. et-al 2003. Conserving Manatees: Knowledge, Attitudes, and Intentions of Boaters in Tampa Bay, Florida. Conservation Biology, Vol 17, Issue 4, 2003, pg 1098.
Burke, Maria. “Seagrasses under threat.” Environmental Science & Technology, v. 38 issue 2, 2004, p. 32.
Christian, C. (2003): Are Manatees Endangered? Outdoor Life; Aug2003, Vol. 210 Issue 6, p13, 1/3p,
Gerstein, Edmund R. Manatees, biacoustics and boats. American Scientist. V.90 No.2 (Mar/Apr. 2002) p.154-63.
Han, Thomas K et-al Effects of Brevetoxins on Murine Myeloma SP2/O Cells: Aberrant Cellular Division; International Journal of Toxicology; Mar2003, Vol. 22 Issue 2, p73, 8p
McClintock, Jack. The virus, the manatee and the biologist. Discover v.24 issue 8, 2003, p.42.
Davidson Osha. G (1998). The Enchanted Braid: Coming to terms with Nature on the Coral Reef. New York, NY: John Wiley & Sons, Inc.
Florida’s Manatees, Earthwatch Research Institute Journal, 15264092, 2002. Research & Exploration, Vol.21, Issue 3
Florida Manatee Mandate: Sierra; May/Jun2003, Vol. 88 Issue 3, p52, 1/2p
Manatees in Belize: Earthwatch Institute Journal; Jan2004, Vol. 23 Issue 1, p57.
Save The Manatee Club: http://www.savethemanatee.org/
“60 Manatees Killed by Red Tide.” New York Times, v. 152 issue 52457, 2003, p. A12.
For Further Info on this Topic, Check out this WWW Site: http://www.savethemanatee.org/.
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