Although there are 35 species of seals,
only six types live in Antarctica:
Antarctic Fur Seals, Crabeater Seals,
Leopard Seals, Ross Seals, and Weddell
Seals. However, these six species
make up the majority of the world's
seal population. With no natural land
predators, such as polar bears or
man, Antarctic seals behave much differently
than northern seals--showing little
fear of man.
Seals are categorized into three
families: true seals, eared seals
(common to most zoos), and walruses
(found in the arctic). All of the
seals in Antarctica are true seals
(no ears). Even without ears, seal
hearing out of the water is as good
as human's. In the water, their
hearing is even better. Its theorized
that seals use a type of sonar to
locate food, much like what dolphins
and whales use.
In addition to using sonar for
navigation and locating groups of
food, its believed seals use their
whiskers as a form of radar. The
whiskers detect movement in the
water and allow the seal to zoom
in a particular object. Through
the use of their sonar and radar,
seals can actually find food in
complete darkness better than in
the light.
As for their eyes, seals don't
really see color but they are particularly
sensitive to common sea water colors
(greens, green-blues). Seals eyes
have a silvery lining behind the
retina, just like cats and other
nocturnal/low-light hunters. This
lining reflects the light back through
the eye and increases the total
amount of light absorbed by the
eye--another necessary feature when
hunting in the dimly lit depths
of the oceans.
When in the water, a seal's nose
closes automatically and doesn't
reopen until it surface. Typically,
a seal can remain underwater for
15 minutes (young) to 30 minutes
(adults). This also is true of when
they're sleep. Seals sleep just
under the surface of the ocean and
can resurface for air without waking.
Antarctic
Fur Seals
Unlike other seals found in Antarctica,
Fur Seals are not true seals. They
are from the eared seal family. They
reside on the rocky shores of islands
found in western Antarctica and average
adults weigh 350 pounds (160 kilos).
Although extremely sociable among
other Fur Seals, they are known
to bit humans without provocation
and move well enough to outrun humans
on land. These poor manners were
not helped by the fact that Fur
Seals were heavily hunted during
the 19th century. At one point,
their total population was reduced
to a few thousand.
Fur Seals were placed under protection
at the beginning of this century
and have made a remarkable recovery.
Their breeding season begins in
December and takes place in very
large, dense colonies. At colonies
on South Georgia Island, seal populations
increase by an average of 17% a
year. This translates to their population
doubling every five years.
Crabeater Seals
Despite their name, Crabeaters eats
mainly krill; crabs form only a small
portion of the seals' diet. Crabeaters
live at the edge of pack ice and are
normally solitary animals. However
during the breeding season, they will
form small family groups consisting
of the mother, father and a pup.
The Crabeater seal accounts for
over half of the world's seal population.
Estimates place the Crabeater's
population in excess of 30 million.
Its population explosion is possibly
due to the decline of whales, the
Crabeater's chief competition for
krill.
The Crabeater's main predator is
the killer whale (or orca). Occasionally
whales will bump an ice floe which
has seals on it in order to knock
seal into the water. Leopard Seals
also prey on the Crabeater, although
typically only on the young.
Leopard Seals
Leopard Seals are the largest
of the true Antarctic seals. (Southern
Elephant Seals are more common on
islands near and above the Antarctic
Convergence, although they do venture
south to the actual continent.)
Leopard Seals can grow to over 11
feet long (3.4 meters) and weigh,
on average, 1,200 pounds (540 kilos).
They are rather easy to identify
due to the reptilian-like head,
long sinewy neck, and arched thorax.
Although commonly found on pack
ice, leopard seals spend a good
deal of their time patrolling the
shores of penguin rookeries. Warm-blooded
animals account for nearly 40% of
the leopard seals' diet. Typically,
they feed on penguins and small
Crabeater seals. The remainder of
their diet consists of krill (approximately
40%), fish, squid, and other invertebrates.
Ross Seals
Because of its tendency to live
on heavy pack ice where ships cannot
pass, little is known about this
species. What is known is they're
nearly as large as Leopard Seals.
Females Ross Seals can reach 11
feet in length (3.3 meters) and
weight an average of 420 pounds
(190 kilos). As with most Antarctic
seals, males tend to be smaller.
Ross Seals are identified by the
short heads and rather large eyes.
Also, there often are strips starting
at the chin and running along the
sides of the neck to the chest.
Their diet consists mainly of fish
and squid, although they're not
opposed to eating other invertebrates.
Due to the lack of knowledge about
them as well as their infrequent
sightings, Ross Seals are protected
under the Antarctic Treaty.
Southern Elephant
Seals
These are the big daddies of the
Antarctic beach. Elephant Seals
can tip the scale at a hefty 7,900
pound (3,600 kilos) and measure
up to 15 feet (4.5 meters). They
commonly are found throughout the
sub-Antarctic islands, although
some colonies are located near the
continent.
Being larger in this specie, males
dominate the breeding process. They,
first, battle with other males to
establish territory on the beach.
To the victor goes the spoils; this
includes harems which can include
up to 50 females. Breeding colonies
are terribly cramped for space.
These multi-ton beasts lie next
to and on top of each other. Often,
pups are crushed under the weight
of adult seals.
In order to satisfy their huge
appetites, Elephant Seals dive deep
into the ocean and feed on various
forms of fish and squid.
Weddell Seals
One of the more commonly sighted
seals, Weddells often are found
in groups. Some of these groups
contain several hundred seals, although
this typically occurs during their
breeding season (September to November).
During this time, males engage in
numerous territorial battles.
Unlike other species, these seals
prefer to lie on snow and ice even
when open land or rock is available.
This trait, along with their desire
to avoid Orcas, is one of the primary
reasons Weddells are found on inland
fast ice around the continent.
During the winter months, Weddells
must maintain diving/breathing holes
in the ice in order to feed. Feeding
primarily on fish, Weddells can
dive in excess of 1,000 feet (300
meters) in search of food. To make
these long dives possible, they
carry five time the amount of oxygen
in their blood as human do. To get
the most from this, Weddells slow
their heart rate and limit blood
circulation to vital organs such
as the brain, kidneys, and liver.
content provided by "http://lrs.ed.uiuc.edu/students/downey/project/seals.html"
for informational purposes.
