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Lee Meiners
Tropical Marine Ecology 2004
Dr. Hays Cummins
June 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
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.
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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
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
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.
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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
(Save the Manatee Club.)
Dating back to 1893, the West Indian Manatees have
been protected by
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
a Òrefuge and sanctuary for the manatee.Ó
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
Spring
State Park
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
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 areasÕ 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
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
and Crystal River/Kings Bay in
County
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
á
Manatees love chewing the end of ropes to clean their teeth and
massage their gums
á
Manatees sleep underwater continually rising (while asleep) to the
surface to breathe
á
Manatees can stay submerged as long as 25 minutes
á
Manatees seek out human interaction, they like to get their bellies and
flippers scratched
á
Manatees teeth fall out and re-grow continually due to eating
habits
á
Contrary to popular belief, death from boats is caused primarily
by impact against the hull, not the propeller cuts
á
The difference in color between manatees is caused by the growth of
algae on their skin
á
Researchers believe the growth of algae explains the manatees
constantly shedding skin that combats the growth
á
Their stiff whiskers are used to help them ÒsenseÓ 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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