Page 236 - NS-2 Textbook

OCEANOGRAPHY 231

alone, there are at least 5,500 square kilometers of shal- wide (100 million acres) were converted to aquacultural
low sea that could be turned over to milkfish production. development, the potential yield would equal the maxi-
Such production could supply most of the mmual protein mum considered natmally possible from the world's
requirements of Asia. oceans-100 million tons each year.
Over a thousand years ago the Chinese developed a Freshwater commercial fish farming in the United
complex ecological fish farming system that they still use States has become more md more popular and success-
today. They place six different kinds of carp into a single ful since World War II. The varieties most commoniy
deep pond, knowing that each species occupies a differ- raised in ponds or basins are trout, walleyed pike, perch,
ent habitat (water depth) and consumes different food. atld catfish. Most freshwater fish now seen in the frozen
The grass carp consumes the surface vegetation. 11,ere fish counters of supermarkets are products of these fish
are two mid-water dwellers, one that eats zooplatlkton, farms. Most of the pike are raised in Canada, Upper
the other phytoplankton. Finally, there are three bottom Michigatl, atld Wisconsin. Trout are raised throughout
feeders that eat mollusks, worms, and the feces of the the country, but mostly in the motmtain areas atld north-
grass carp. This is m extremely efficient ecological sys- ern part of the country. Catfish and perch are raised in
tem that even serves to eliminate "pollution." The sys- the South atld Southwest. Aquaculture is currently the
tem is mcient, but it is naturally orgmic-md it works. fastest-growing sector of agricultural production in the
Woods Hole Ocemographic Institute in Massachusetts United States.
has worked out a sinlilar system involving algae, oysters,
seaweed, abalone! sand "vorms, and flolUlder, after which SEA NOISES
clem water is returned to the sea. The main crop is oysters,
with abalone md flounder as secondary crops. It is a nat- An interesting biological phenomenon in the oceans is
ural sewage treatment platlt. The sewage is used to grow the "deep scattering layers." Discovered in World War II,
platlkton algae, which in turn provide food for oysters. The these layers have become increasingly inlportatlt to
waste from the oysters is consumed by seaweeds, which is mariners atld oceatlographers. Scientists experimenting
then fed to abalone. The remainder that faIls to the bottom with marine sound detection gear recorded echoes from
of the tatlk is eaten by satld worms, which are then circu- layers some distance above the ocean floor. Dming day-
lated to a neighboring tatlk to serve as food for flounder. light hours there are usually three distinct layers that re-
The system is designed to produce 1 million pounds of main at depths from 700 to 2,400 feet. At night they rise
seafood meat annually from a one-acre production facility ainlost to the surface and diffuse, or they may merge into
of fish atld shellfish holding tmks, md a fifty-acre algae a broad batld as much as 500 feet thick.
farm using sewage from a community of 11,000 people. After some years of research, ocemlographers de-
In Southeast Asia, in addition to the milkfish farming duced that there seemed to be a close parallel between
described above, the people also harvest mullet, shrimp, the layers atld the daily vertical migrations of certain ma-
and crabs in ponds constructed by clearing matlgrove rine animals. Today, this theOlY has generally been ac-
swamps md diking them with mud. These are extremely cepted, though there is still much to be learned about the
productive. The small fry are first fed in a nursery pond, phenomenon. It is believed that huge concentrations of
while algae, bacteria, worms, atld other platlkton are tiny planktonic aninlals rise toward the surface to feed
raised naturally in production ponds with the addition on phytoplatlkton, atld then, at daybreak, seek the dark
of fertilizer. When the fly get to fingerling size, they are depths for protection from sunlight and predators. It ap-
transferred to the production ponds. There they literally pears that the layers are composed of a wide variety of
gorge themselves, growing to mahlre size in just a few zooplatlkton, including tiny fish, shrimplike animals,
months. The average yield of such ponds is about 500 lantern fish, fish with bladders or gas-filled bubbles, atld
pounds per acre. tiny jellyfish with gas-filled floats. Biologists consider the
Aquaculture is not limited entirely to fish. Along the layers to be inlportant in explaining the distribution of
Pacific coast of Asia, people have been supplementing life within the sea.
their diets with a variety of seaweeds for ages. It is mixed These deep scattering layers create horizontal sound-
in rice dishes and used as greens and seasoning. It is reflecting bands at various depths over broad stretches of
highly nutritious md excellent tasting. Some giant algae the world's oceans. Until the phenomenon was identified,
have been used for centuries as fertilizer for farnl crops it caused confusion to operators of echo-sounding de-
md as cattle food. Giant kelp plants of the Pacific are vices and sonar equipment. hl addition, lllany marine an-
processed for iodine, medicines, and a variety of other imals have sound-emitters that create a wide assortment
products that are used in cosmetics, textiles, ink, papel~ of noises beneath the sea. A person on the surface does
paints, drugs, and food presenratives. not hear the noises because of the frequencies and sound
Woods Hole has estimated that if only one-tenth of level at which they are transmitted, but they cm become
the 1 billion acres of available coastal wetlands world- a constatlt clatlgor over hydrophones. Such noises must