ENDANGERED

SPECIES

This Species is Protected Under the
Endangered Species Act of 1973

WEST INDIAN

MANATEE

Trichechus manatus

hristopher Columbus was the

first European to report seeing a

manatee in the New World. To
Columbus, and other sailors who had
been at sea for a long time, manatees
were reminiscent of mermaids—the
mythical half-fish, half-woman creatures
of the ocean. Manatees are not fish,
however, but marine mammals.

The West Indian or Florida manatee
(and sometimes called sea cow) is found
primarily along the coast of Florida.
Most adult manatees are about 10 feet
long and weigh 800 to 1,200 pounds,
although some larger than 12 feet and
weighing as much as 3,500 pounds have
been recorded. These “gentle giants”
have a tough, wrinkled brown-to-gray
skin that is continuously being sloughed
off. Hair is distributed sparsely over the
body. With stiff whiskers around its
mouth, the manatee’s face looks like a
walrus without tusks.

The manatee maneuvers through the
water moving its paddle-like tail up and

down and steering
with its flippers. It is
very agile for such a large animal,
sometimes somer-saulting and doing
barrel rolls in the water.

The manatee often rests suspended
just below the water’s surface with only
the snout above water. It feeds under-
water, but must surface periodically to
breath. Although the manatee can
remain underwater for as long as
12 minutes, the average time is
4% minutes.

Manatees are herbivores, meaning
they eat only plants. But they eat a
great variety of aquatic plant species,
including water hyacinth and hydrilla.
Manatees must eat 4 to 9 percent of
their body weight each day. That's at
least 32 pounds of plants per day for an
800-pound manatee! To do this, they
spend 5 to 8 hours a day eating.

Manatees spend their lives moving
between freshwater, brackish, and salt-
water environments. They prefer large,

slow-moving rivers, river
mouths, and shallow coastal areas such
as coves and bays. Great distances may
be covered as the animals migrate
between winter and summer grounds.
During the winter, manatees congregate
around warm springs and power plants
that discharge warm water. During
summer months, they have occasionally
been seen as far north as Virginia and
Maryland.

Manatees reach breeding maturity
between 3 and 10 years of age. The
gestation period is approximately 13
months. Calves may be born at any time
during the year. Usually only one calf is
born, but twins do occur. Newborn.
calves weigh 60 to 70 pounds and are
4 to 4 feet long. They nurse under-
water for about 3 minutes at a time
from a nipple located behind their
mother’s forelimb. Born with teeth,
calves begin eating plants within a
few weeks but remain with their
mother for up to 2 years.

Most adult manatees are about 10 feet long and weigh 800 to 1,200 pounds, although some larger than 12 feet long and weighing as much as 3,500 pounds have
been recorded. Many of the remaining manatees bear scars from encounters with boat propellers —a leading cause of manatee deaths.

ee

“hts



Atthough twins do occur, an adult female manatee
will usually have one calf every 2 to 5 years. The
manatee’s low reproductive rate makes it less capa-
ble of rebounding from threats to its survival. In
General, the birth rate is not able to keep up with
those manatees killed by boats.

Manatees communicate with each
other by emitting sounds underwater
that are audible to humans. The vocal-
izations, which sound like squeaks and
squeals, are especially important for
maintaining contact between mother
and calf. One field report described a
mother and her calf, separated by a
flood gate, calling to each other for
3 hours without interruption until
they were reunited.

Historically, manatees were hunted
for the flesh, bones, and hide by Native
Americans and later by the early
colonists. Manatee fat was used for
lamp oil, bones were used for medicinal
purposes, and the hide for leather. This
hunting is thought to be largely respon-
sible for the manatee’s initial decline.

Natural events also imperil the lives
of manatees. In 1977, 1981, 1984, and
1989, unusually cold winters lowered
water temperatures throughout Florida,
killing many manatees, which cannot
survive long in cold water. As the water
temperature drops below 60°F, mana-
tees become sluggish and stop eating.
Young manatees are especially suscepti-
ble to the effects of cold temperatures.

Periodic red tide blooms have also
been associated with a number of mana-
tee deaths. Red tide toxins accumulate
in sea squirts which adhere to sea
grasses. This poison is ingested inciden-
tally by manatees feeding on sea grasses.

But the largest problems facing the
manatee are caused by man. Speeding
boats run over many manatees that are
submerged just below the surface,
killing them either by impact with the
boat itself or by slicing into their backs
with the propellers. Manatees that sur-
vive such encounters carry distinctive
scars (in fact, biologists studying the
manatee use the scars as ways of identi-
fying individual manatees). Many areas
now post speed-limit signs for boaters,
or prohibit them completely in areas
heavily populated by manatees.

Flood gates and canal locks have
accidentally killed manatees either by
crushing or drowning them, although

modifications of operating procedures
have reduced the number of fatalities
from this source. Fishing line and other
trash discarded into the water are also
responsible for a small number of mana-
tee deaths each year. Death may result
if the manatee’s digestive tract becomes
blocked by fishing line accidentally
eaten. Fishing line may also become
tightly wound around a flipper, creating
serious infection, amputation, or at
worst, death.

Harassment from skin divers, fisher-
men, and boaters can interrupt feeding
and mating activities. During the win-
ter, manatees may be driven into cooler
water where they are more susceptible
to disease and cold stress.

The manatee has difficulty rebound-
ing from these threats because of its late
breeding maturity and its low reproduc-
tive rate. In general, the birth rate is not
able to keep up with those manatees
killed by boats.

Manatee population counts are usu-
ally conducted from airplanes. It is diffi-
cult to obtain an exact population
figure because poor weather or murky
water conditions make it difficult to
clearly see the manatees. In 1992, 1,856
manatees were counted by aerial sur-
veys conducted throughout the mana-
tee’s range.

Biologists use radio tracking to study
individual manatees, locate and assess
habitat use areas, and learn about
migratory patterns.

As long ago as 1893, Florida passed a
law to protect manatees. Since 1907,
there has been a $500 fine for any person
who kills or harms a manatee. In 1978,
Florida designated the entire state as a

“refuge and sanctuary for the manatees”
through the Florida Manatee Sanctuary
Act. This law allows the State of Florida
to designate manatee sanctuaries and
establish speed zones for boats.

At the Crystal River National
Wildlife Refuge on Florida’s West Coast,
boats are required to reduce their speed
and, during the winter when manatees
congregate, boats, swimmers, and divers
are prohibited in certain areas.

The manatee was listed as an endan-
gered species in 1967 (under a law that
preceded the Endangered Species Act
of 1973), meaning it is considered in
danger of extinction throughout all or a
significant portion of its range. The
manatee also is protected at the federal
level under the Marine Mammal
Protection Act of 1972.

A vital component of the U.S. Fish
and Wildlife Service's recovery efforts for
the manatee is increasing public aware-
ness and cooperation among boaters,
skin divers, fishermen, and anyone else
using the rivers and coastal waters where
manatees live. With growing awareness
and positive action, the manatee can be
saved for generations to come.

BIOLOGUE SERIES

Prepared by:

U.S. Department of the interior
U.S. Fish and Wildlife Service
1995