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Marine mammals have the same characteristics as all other mammals, but they have adapted to living all or part of their life in the ocean. To keep warm in the ocean, most of them depend on a thick layer of blubber (or fat). They have streamlined bodies to help them swim faster. Many species can stay under water for a long time, but must come to the surface to breathe. To be able to stay under water for long periods, they store extra oxygen in their muscles and blood.
Marine mammals also have more blood than land mammals in proportion to their body sizes, can direct their blood flow to only their vital organs (such as their heart and lungs), and can slow their heartbeat down so they are using less oxygen in a dive.
Unfortunately, many marine mammals are considered endangered species and there are still threats to most of their populations, such as illegal hunting, pollution, climate change, and habitat loss.
There are five groups of marine mammals: pinnipeds (seals, sea lions, fur seals, and walruses), cetaceans (whales, dolphins, and porpoises), sea otters, sirenians (dugongs and manatees), and polar bears.
The word pinniped means fin or flipper-footed and refers to the
marine mammals that have front and rear flippers. This
group includes seals, sea lions, and walruses. These animals
live in the ocean but are able to come on land for long periods
of time. Millions of years ago, the ancestors of pinnipeds
lived on land. These were probably weasel or bear-like animals
that spent more and more time in the ocean and eventually
adapted to this marine environment.
There are three families of pinnipeds: phocids (seals), otariids
(sea lions) and odobenids (walruses). There are many different
kinds of true seals, but you can always recognize them by
looking at their ears and flippers. True seals have ear holes
but no external ear flaps. They also have small front flippers
and move on land by flopping along on their bellies. At sea,
they move their rear flippers back and forth like a fish's tail
to propel themselves through the water.
Marine mammals in the cetacean family include whales, dolphins,
and porpoises. Although whales spend all their time in the
oceans, they are mammals just like us. This means that they are
warm blooded, give birth to live young, nurse their young, have
traces of hair or fur, and must come to the surface to breathe
air through their lungs.
Cetaceans are separated into two groups: toothed and baleen
whales. As their name suggests, toothed whales (or odontocetes)
have teeth. They also have one opening at their blowhole. There
are over 73 species of toothed whales, including sperm and
beaked whales, belugas and narwhals, porpoises and dolphins, and
even fresh water dolphins that live in rivers. They range in
size from the 60-foot (21.1 m) sperm whale to the 5-foot (1.5 m)
vaquita. Some toothed whales are quite unusual. For instance,
the beaked whales spend most of their time in the deep water
and, therefore, are rarely encountered by people, and new
species are still being discovered! Some beaked whales are odd
looking and often only the males will have teeth. The
straptoothed whales have only two teeth, which wrap around the
top of their jaws so they cannot fully open their mouths!
The baleen whales (or mysticetes) are the other group of
cetaceans. This group includes 11 species ranging in length from
the pygmy right whale at 21 feet (6.4 m) to the largest whale,
the blue whale at 100 feet (30.5 m). Baleen whales have two
blowholes and instead of teeth, have hundreds of rows of baleen
plates, which are made of keratin, a substance in our hair and
fingernails. The baleen strains out small fish and plankton from
the water for food.
There are eight species of whales that frequent the cold and
icy waters of Alaska. The Beluga,
Humpback,
Gray, Orca,
Bowhead, Blue,
Right, and
Minke whales.
Sea otters are members of the weasel or mustelid family. Like
other members of this family, they have very thick fur. In fact,
at 850,000 to one million hairs per square inch, they have the
thickest fur of any mammal. Their fur actually consists of two
layers, an undercoat and longer guard hairs. This system traps a
layer of air next to their skin so their skin does not get wet.
Sea otters are usually dark brown, often with lighter guard
hairs. Alaskan sea otters tend to have lighter fur on their
heads. Sea otters are the smallest marine mammal.
Polar bears are the largest carnivores and a unique symbol of
the Arctic. Nineteen populations of polar bears are distributed
in Alaska, Canada, Greenland, Norway, and Russia. The world wide
population is estimated to be 22,000-25,000 bears. Two
populations occur in Alaska: the southern Beaufort Sea stock,
shared with Canada; and the Bering Chukchi/Seas stock, shared
with the Russian Federation
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