Page 233 - NS-2 Textbook

228 NAUTICAL SCIENCES

Arctic. There are only about 2,000 polar bears living in In order to help conserve the remaining numbers of
the wild today because of overhlillting. the various species of marine manunals, Congress passed
The sea otter has webbed feet and is well adapted to the Marine Mammal Protection Act in 1972, which pro-
life in the sea. It inhabits only the coastal regions of Cali- hibits U.S. citizens from hunting any of these anintals in
fornia and Alaska, where it feeds in the giant kelp beds U.S. waters or on the high seas, or from inlporting them
on abalone and sea urchins. The sea otter spends most of and any products made from them into the United States.
its life at sea, sleeping, eating, and even giving birth to its In 1994 certain of their numbers had increased sufficiently
young among the kelp. It was almost exterminated for its that the act was amended to allow for hunting by Alaskan
valuable pelt by the early 1900s, but strict hunting regu- natives for subsistence, and for commercial fishermen to
lations have allowed it to make a good natural recovery. kill fuose that were inadvertently captured or injured inci-
Other marine mammals, however, have changed a dental to commercial fishing operations.
great deal from the form they once had on land. There Whales, dolphins, and porpoises are all air-breathing
are three groups: the sea cows, the seals, and the whales. mammals that bear their young alive, nurse them, and
TI,e sea cows include the manatees of Florida and the maintain a constant body temperature. They spend their
jungle rivers of South America. The sea cow eats lily lives entirely in water and breathe through openings
pads. It is cigar shaped with front flippers and a flat tail called blow-holes. Movement is aided by horizontally flat-
but no hind flippers. tened fail flllkes. There are two subgroups of whales: the
There are three groups of seals: the earless, or true, baleen, or whalebone, whale and the toothed whale.
seals; the eared seals, or sea lions; and the walrus. They Instead of teeth, the baleell whales have a fine mesh
are all fish-eaters and have streanilined bodies and limbs sieve with up to 800 or more plates of baleen or whale-
modified to be flippers. They are fast, expert swinlmers bone that hang like a curtain from the upper jaw. When
and can easily catch their prey in the water. They have a feeding, the whale opens its jaws. When the jaw closes,
layer of thick blubber beneath the skin to protect them the baleen allows the water to flow out but keeps any
from the cold. The fur seals of Alaska have luxuriant collected marine life in. The main foods of the baleen
pelts much prized for coats. After many years of over- whale are plartkton and krill (a shrimplike animal that
hunting, they are now carefully protected and "har- grows up to 2-3 inches long and is found in large num-
vested" for their pelts, a valuable natural resource. The bers in Antarctic waters). Baleen whales range in size
California sea lion is the most common performer in from the minke (just over 30 feet) to the blue whale,
zoos. The walrus has long ivory tusks and is found only which often grows to 90 or 100 feet in length and
in Arctic waters. weighs 100 tons. The giant blue whale, the largest mam-
mal that has lived on the Earth, weighs 2 to 3 tons at
birth, doubles its weight in its first week of life, and
seven months later weighs about 24 tons! The largest
blue whale on record was 108 feet long. From a world
population of about 40,000 in 1930, there are now only
a few thousand left. Some conservationists fear it is
close to extinction because its death rate may soon ex-
ceed its reproductive rate.

Giant 1 ~-ton elephant seals bask in the sun on an Antarctic beach.
Ungainly on land, they are fast swimmers in the water, able to catch A blue whale comes up for air in the Queen Charlotte Strait off the
fish to eat. Pacific coast of Canada. This species is the largest mammal on Earth.