The Florida
manatee is a subspecies of the West
Indian manatee. It is a large, gentle, grayish-brown
mammal that spends its entire life in the water feeding
on seagrass. It frequents the coastal waters of Florida,
particularly in winter, but its range extends north
to Virginia and west to Louisiana. Stray individuals
have been spotted in summer as far north as Rhode
Island and as far up the Mississippi as Memphis.
The manatee's preferred habitat is shallow, coastal
waters, estuaries, canals, and slow-moving rivers.
They flourish in warm waters with a depth of 1 to 5
meters. Manatees tolerate differences in salinity,
and thus can inhabit both fresh and saltwater.
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| Florida
Manatee calf with neonatal folds, Trichechus
manatus latirostris, endangered
subspecies of the West Indian
manatee, Kings Bay, Crystal River,
Florida. |
Image
#: 029277 |
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Kingdom:
Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Mammalia
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Adult manatees are 3 meters long on average (10 ft),
and weigh an average of 500 kg (1,100 lbs). Some individuals
reach a length of 4.6 meters (15 ft), and a weight of
1,000 kg (2,200 lbs) or more. Females are typically larger
and heavier than males. Manatees have flexible, split
upper lips which pass food into their mouths. Their skin
is wrinkled and they have whiskers on their snouts. Individual
hairs appear sparsely on their bodies, and their skin
continually sloughs off, which may help to reduce algae
build-up.
The forelimbs of manatees are narrow flippers, used
for steering and maneuvering along the muddy sea floor.
These flippers each have 3 or 4 nails, which are reminders
that manatees are distantly related to elephants. Manatees
have no hind limbs, though they do have vestigial hind
limb bones floating in their hind area muscle. Their
tails are round, flat paddles used for propulsion.
Though manatees appear fat, they are actually highly
muscular, and are very agile in the water.
Manatees move slowly and spend most of their time
eating, resting and migrating. They have a low metabolism
and consume about 10-15% of their body weight daily.
To achieve this rate, they must eat for 6 to 8 hours
each day.
Manatees must surface to breathe every 2 to 4 minutes,
or much more frequently-every 30 seconds-when active.
Each breath renews about 90% of the air in their lungs,
as opposed to about 10% for humans. Their nostrils
are valved and located at the top of their snouts.
The hearing of manatees is good, and mothers and calves
communicate by means of squeals and bleats. Manatees
have no pinnae, or ear flaps. Eyesight is poor, though
they do use their eyes for navigation. Their eyes are
protected by means of a nictitating membrane, and they
can be closed with a sphincter-like contraction.
The abrasive sea plants consumed by manatees cause
their teeth to wear down. As a result, they have evolved
molars which are continually replaced throughout their
lives. The seagrass they eat ferments in their hind-gut,
contributing to digestion.
Manatees have a slow reproductive rate. Females reach
sexual maturity at about 5 years of age, and males
at 9. They give birth to one calf every 2 to 5 years,
and only occasionally have twins. They have a 13-month
gestation period and calves stay with their mothers
for up to 2 years. Calves nurse from their mothers
from two teats located under the forelimbs.
Manatees are not considered territorial, and generally
exist alone or in loosely connected groups. Pairs seen
together are typically mother and calf. Large groups
of manatees sometimes gather near the warm waters discharged
by electric power plants.
Historically, manatees have been hunted for their
meat, hide and bones. In modern times, they face the
extreme danger of collisions with motorboats, and many
manatees in and around Florida can be identified by
the propeller scars on their backs. Manatees are also
threatened by loss of habitat, which is often due to
agricultural and industrial runoff. Other dangers include
entrapment in flood gates and canal locks, red tides,
and cold stress. They have no known predators other
than man.
No one knows how many manatees exist today. Surveys
of Florida manatees show a population of between 2,500
and 3,000 individuals and they are considered endangered.
Manatees are the state mammal of Florida, and Florida
is now a marine sanctuary for manatees. There are fines
for killing a manatee, and they are protected by the
U.S. Marine Mammal Act (1972), the Florida Manatee
Sanctuary Act (1978), and the U.S. Endangered Species
Act (1973).
For an illustration comparing species and species
size in the order Sirenia, see: http://www.sirenian.org/caryn.html
- Florida manatee information assembled from published
and on-line sources by Kevin
Miller on Oct. 24, 2006 for SeaPics.com.
Sources:
Ripple,
J. Manatees and Dugongs of the World, Voyageur Press,
1999.
http://marinebio.org/species.asp?id=46
http://animaldiversity.ummz.umich.edu/site/accounts/information/Trichechus_manatus.html
http://www.sms.si.edu/IRLspec/Trichec_manatu.htm
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