Page 232 - NS-2 Textbook

OCEANOGRAPHY 227

throughout the seas, but most live in the shallow, Twenty-three species of crocodiles inhabit much of the
warmer seas. Within this group are five subgroups: (1) waters of the tropical zones around the world. TIlese in-
bottom-living fishes of both shallow and deep seas, clude the American alligator, found in marshes, s"\vamps,
which have large heads and whip tails; (2) large carnivo- rivers, lakes, tidal areas, and sometimes the ocean in the
rous fishes with tough, leathery skins and sharp cutting southeastern United States; the American crocodile,
teeth, such as the sharks and rays; this group includes the found in southern Florida, Central America, South
largest fish-the whale shark, basking shark, and manta Anlerica, and various Caribbean islands; and 21 other
ray; (3) sturgeons, which have bony plates on the skin species found in Asia, Africa, Aush'alia, and other Pacific
and are commercially valuable for their eggs, called and Indian Ocean regions. They are very hardy, tough
caviar; (4) the largest group, which includes most com- animals that have survived, basically tffichanged, from
nlercial fishes, such as cod, herring, turbot, salmon, hma, prehistoric times. They range in size from a few feet to as
mackerel, flounder, bass, and many others; and (5) lung- long as 20 feet or more. TIle smaller ones feed on insects,
fish, three of which are freshwater types, and one called snakes, turtles, slow-nloving fish, small mammals, and
the coelacanth. This oddity, once thought to have died out birds. Large adults may eat larger mammals and, on oc-
some 50 million years ago, was found in the Indian casion, may attack tm,vary people.
Ocean in 1938. An occasional specimen has been caught The seabird group includes a number of different
from time to tinle since. species. The waders live and feed along the shallows, in
TIle reptile group has only a small number of species eshmries of rivers affected by tides, in ponds, and in
that live in the sea today-a far cry from the Age of Rep- mangrove swamps. Birds of the open sea, such as the al-
tiles, when they were the dominant form of life in the batross and petrel, live most of the time in the open
world ocean. Reptiles are cold-blooded. That means they ocean, coming ashore only to breed. The emperor pen-
cannot regulate their temperatures as mammals do, so guin lays its eggs on sea ice in Antarctica. It is the only
they usually inhabit warm tropical seas. There are four bird that never comes ashore. There are many other vari-
groups of living marine reptiles: turtles, marine iguanas, eties of penguins, all of them in the Southern Henti-
sea snakes, and a few ocean crocodiles. sphere. Seabirds feed mainly on fish. As penguins cannot
Sea turtles grow to a huge size. The rare leatherback fly, they catch fish by diving and swimming. Pelicans
sometinles exceeds 6 feet in length and weighs over half and gannets catch them by diving. Gulls and terns spot
a ton. Turtles swim with flippers. They come ashore to and then pounce on their prey from the air.
lay their eggs in holes dug in the sand. There, they are at The mammal group has a limited number of marine
the mercy of many different kinds of predators. Few of species, but they are some of the world's most interesting
the young make it back to the sea before being eaten by animals. They include the polar bear and sea otter, which
seabirds. are sinillar in most characteristics to land aninlals but are
Marine igllanas live only in the Galapagos Islands of adapted to the sea. The polar bear has extra-long legs,
Ecuador, off the west coast of South America. They are which makes it a powerful swilruner, and a thicker coat,
the only marine lizards. They live in large herds on the which insulates it against the icy waters and winds of the
rocks near shore and feed on seaweed.
Sea sl1akes are poisonous, some related to cobras and
kraits. They have paddlelike flat tails so they can swlll.
TIley inhabit sheltered coastal waters, especially near
river mouths, and some live in brackish water up-
stream. There are nearly fifty species of these poisonous
snakes living in the tropical Pacific and Indian Oceans.
They range from East African waters throughout south-
ern and Southeast Asia, Oceania, Australia, and in the
warm Japan Current all the way north to Japan and
Korea. A few species exist along the Pacific coast of
Central and South America. Although sea snakes are
poisonous, they do not disturb swimmers and are said
not to bite unless forcibly restrained. They feed on fish,
mostly at night. This makes them dangerous to fisher-
men who may net them when they are attracted by
schools of fish and the lights of fishing boats. Asian
fishermen are said to throw them from their nets with
A mother Adelie penguin and recently hatched chick at Mammoth
bare hands. There are a number of deaths caused by sea Penguin Rookery on Mount Bird, Ross Island, Antarctica. Penguins
snakes each year. cannot fly but are excellent swimmers.