Saving the West Indian Manatees

This topic submitted by Lee Meiners ( meinerlm@miamioh.edu) at 4:34 PM on 6/10/04.

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Tropical Field Courses -Western Program-Miami University


Lee Meiners


Tropical Marine Ecology 2004


Saving the West Indian Manatees


The fact that many species, including the manatee, are declining is not the problem.  The decline of species is symptomatic of a greater problem-namely habitat loss from human encroachment and development.  More people in Florida mean more development and greater strain on its finite natural resources.  The result is loss of habitat, habitat degradation and species decline.             Judith Vallee, executive director Save the Manatee Club


The West Indian Manatee, or Trichechus manatus, has been listed as endangered since 1967 and continues to face serious threats from boat collisions and destruction or degradation of habitat caused by widespread development throughout Florida.  As of February 2004, there are approximately 2, 568 manatees in Florida's wild waters. In 2003 alone, 91 manatees were killed by collisions with boats. I plan on discussing manatees in their current state of endangerment and possible ways to save them.  I will start by giving general information about the manatees such as physical characteristics, species, and interesting facts.  I will discuss their location, habitats, and migratory patterns, as well as their birth/death rate, population trends, and current research and tracking projects.  I plan to discuss threats against the manatees, current conservation actions, protection, and a future outlook for Trichechus manatus.                                                  







           


        The West Indian Manatee is a large gray or brown aquatic mammal.  An adult manatee averages about 10 feet long weighing approximately 1,000 pounds.  Their forelimbs are modified as flippers, and they have no hind limbs.  Sparse hairs cover their entire body and their muzzles are covered with stiff whiskers.  The sex of the manatee is hard to distinguish, only the position of the genital openings and presence or absence of mammary glands differ between sexes.  Trichechus manatus is primarily a herbivore, although they have been known to occasionally feed on fish.  In saltwater, manatees feed primarily on several species of sea grasses, including turtle grass (Thalassia testudinum), manatee grass (Syringodium filiforme) and shoal grass (Halodule wrightii).  They have been known to crop overhanging branches, consume acorns, and haul themselves partially out of the water to consume bank vegetation (Reynolds and Odell 43.)  Manatees spend about 5 hours a day feeding, with no regular feeding schedule (U.S. Fish and Wildlife Service).  They may feed during the morning, evening, or at night, consuming 4 to 9 percent of their body weight a day.  Subspecies include Trichechus manatus latirostris, and Trichechus manatus manatus.  The West Indian manatee can be distinguished from other marine mammals by their large spatulate tail, slow movements, large prehensile lips, and elongate forelimbs (Ruff and Wilson 321.)  The West Indian Manatees emit a squeaky sound underwater which carries about 30 meters (Ridgeway 488.)


        Manatees are found in warm tropical and subtropical waters.  The West Indian manatee can be found as far north as Virginia and as far west as Mississippi or Louisiana during warm summer months.  Its year-round range is restricted to peninsular Florida and possibly southern Georgia.  They can be found in water as shallow as a meter (3.28 feet) inhabiting bays, estuaries, rivers and coastal areas where sea grasses and other vegetation thrive.  Manatees live year round in freshwater and they can survive in saltwater, but for how long is unknown.  Warm water for manatees is a necessity and a matter of survival.  At temperatures below 68 degrees Fahrenheit, manatees stop eating, suffer cold stress and often they will die. This is why they migrate to the coastal areas, rivers, canals and estuaries in Florida and southern Georgia during winter. They especially prefer the slow-moving rivers and shallow coves and bays where there are warm springs and lush sea grass beds. They also converge around power plant outfalls and warm-water discharges. During winter, hundreds of manatees congregate close to Florida Power and Light Company's power plants at Cape Canaveral, Fort Lauderdale , Riviera Beach and Fort Myers , as well as the Tampa Electric Company's Apollo Beach power plant in Tampa Bay (Gagelonia 2.)


         Female West Indian manatees give birth to one calf after about a one-year gestation period. The calf will stay with its mother for the next two years.  A young manatee is able to forage for solid food after about 3 weeks.  A mature female manatee gives birth every 2 to 5 years, and she will hold a stable bond for usually only 9 to 24 months, but in some cases that bond will last years longer.  Little information is available about the lifetime reproductive output of female manatees, although they may live over 50 years.  







         


        The West Indian Manatees remain on the endangered species list, although recent protection programs are allowing a slow increase in the population numbers.  There are multiple threats against manatees, including over exploitation, powerboat collisions, coastal development, and occasional poaching.  West Indian manatees have no natural enemies, and it is believed they can live 60 years or more. Many manatee mortalities are human-related. Most human-related manatee mortalities occur from collisions with watercraft. Other causes of human-related manatee mortalities include being crushed and/or drowned in canal locks and flood control structures, ingestion of fish hooks, litter and monofilament line, entanglement in crab trap lines, and vandalism.  Ultimately, however, loss of habitat and the degradation of habitat is the most serious threat facing manatees today. There are approximately 3,000 West Indian manatees left in the United States (Save the Manatee Club.)


        Dating back to 1893, the West Indian Manatees have been protected by Florida state law, under Ch. 4208.94.  In May 1907, Ch. 370.12 was passed imposing a $500 fine for killing or molesting a manatee, and it also amended earlier legislation to allow capture of manatees for educational and scientific purposes only.  In 1978, the Florida Manatee Sanctuary Act was passed declaring the entire state of Florida a “refuge and sanctuary for the manatee.”  This act has been in effect since 1 July 1978 , and provides regulation on boat speeds in 13 manatee aggregation areas (Dietz 62.)  Also, in 1973 in Blue Spring State Park (a winter congregation area) the Department of Natural Resources prohibited boats and restricted swimming specifically for manatee protection.  Further manatee protection began 11 March 1967 when the manatee was officially listed as an endangered species under the Endangered Species Preservation Act of 1966.  This act covered species in the United States and authorized acquisition of habitat but left protection to the states.  Further, in 1969 the importation of listed species was permitted and extend its scope to cover species worldwide (Zeiller 172.)


MANAGEMENT AND PROTECTION:  



         Based on revised recovery plan (1989) recommendations, the primary objective in the recovery of the Florida population of the West Indian manatee is to reestablish and maintain optimum sustainable populations in natural habitats throughout the manatee's historic range.  To accomplish this primary objective there are several sub-objectives that must be met.  The most common cause of unnatural death is caused by humans.  We need to minimize human cause injuries and mortalities.  We need to rescue, rehabilitate, and safely release sick, injured, or orphaned manatees.  We must minimize mortality from boat collisions, as well as water control structures and poaching.  Through education, we must inform the public of the ways to protect manatees and we must develop bilateral and multilateral agreements with other countries for manatee conservation and research.   The second largest unnatural cause of death for the manatees is habitat destruction.  We must minimize alteration, degradation, and destruction of these habitats used by manatees and monitor these areas’ status.  We need to evaluate potential hazards such as coastal development, outer continental shelf oil and gas excavation, toxicants, dredging, siltation, and power plant failures.   We must also minimize the harassment of manatees from boat and barge traffic, fishing, diving, and swimming in these areas.  Also, continually using aerial surveys and tracking manatee movements and population trends will help us determine what efforts are working and how to improve protection policy. 


        Researchers agree that in two areas in Florida the manatee population is increasing, through both reproduction and migration of manatees from other areas of the state.  These two areas are Blue Spring in Volusa County and Crystal River/Kings Bay in Citrus County.  Both of these areas have been protected for over 30 years and have relatively low boat traffic and slow speed zones in surrounding waterways.  These factors are believed to be the reason manatees in these areas are becoming more populous.  No one yet knows the status of the two remaining manatee regional sub-populations. The data available from these regions is not sufficient to make a statistically reliable estimate of the population trend. The East Coast and Southwest manatee populations may be stable at best or may be declining. This is important because these two regional sub-populations make up the remaining 84% (the vast majority) of the manatee population in Florida (savethemanatees.org.)



INTERESTING MANATEE TIDBITS


Š        Manatees love chewing the end of ropes to clean their teeth and massage their gums


Š        Manatees sleep underwater continually rising (while asleep) to the surface to breathe


Š        Manatees can stay submerged as long as 25 minutes


Š        Manatees seek out human interaction, they like  to get their bellies and flippers scratched


Š        Manatees teeth fall out and re-grow continually due to eating habits


Š        Contrary to popular belief, death from boats is caused primarily by impact against the hull, not the propeller cuts


Š        The difference in color between manatees is caused by the growth of algae on their skin


Š        Researchers believe the growth of algae explains the manatees constantly shedding skin that combats the growth


Š        Their stiff whiskers are used to help them “sense” their surroundings


 



SOURCES


Dietz, Tim. The Call of the Sires: Manatees and Dugongs.
Golden, CO: Fulcrum Publishing, 1992. Source used for initial quote on research paper


Endangered: In the the Wild: Oceans - Florida (West Indian) Manatee, edited 7/2/1996 .


Finney, Dee. Save the Endangered Manatee. Compilation by Dee Finney


Gagelonia, Ruby. The Florida Manatee  [Online Source] http://www.ecofloridamag.com/archived/manatees.htm  


Reynolds and Odell. Manatees and Dugongs: Evolution of Manatees and Dugongs.
New York , Oxford : Facts on File, Inc., 1991.


Ridgway, Sam H. Mammals of the Sea: Biology and Medicine.
Springfield , Illinois : Thomas Books, 1972.


Ruff and Wilson . The Smithsonian Book of North American Mammals.
Washington and London : Smithsonian Institution Press, 1999.


Save the Manatee club. [Online Sources] Multiple online information sources on manatees.


Seaworld Education Department Resource. Manatees: Longevity and Causes of Death.


U.S. Fish and Wildlife Service, Division of Endangered Species [Online Source] http://endangered.fws.gov/i/a/saa0c.html


Zeiller, Warren. Introducing the Manatee: Sirens Sing Ever More Softly.
Gainesville , University Press of

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