The Environmental Science Graduate Students at Watlings Castle, San Salvador, Bahamas.(TME 98)
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
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
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
Manatees are found in warm tropical and subtropical waters. The West Indian manatee can be found as far north as
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
Dating back to 1893, the West Indian Manatees have been protected by
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
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
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 -
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.
Ridgway, Sam H. Mammals of the Sea: Biology and Medicine.
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.
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