Earth’s Waters—an Answer to Food Shortage?
EARTH’S soaring population means tens of millions of new mouths to feed each year. Yet even now many people are starving, and others are hungry. Where can the food to feed everyone be obtained?
It is commonly believed that earth’s waters are an adequate source. One writer asserted: “There is no need for anyone on earth to go hungry when there is a vast, practically untapped and possibly unlimited supply of food in the sea.” But is this true? Do the seas have a sufficient food supply?
Food Potential of the Seas
The amount of food taken from earth’s waters has increased dramatically. From less than 19 million metric tons in 1950, the annual harvest has increased to over 60 million metric tons. That may seem like a lot. However, it is estimated that this amounts to only a little more than 3 percent of the total human food produced. Can the sea yield much more?
Some persons noting the vastness of the sea—it covers nearly three-quarters of the earth—have assumed that it can. But there is a fact that some fail to consider. And that is that most of the sea is virtually unproductive of food, even as is most of the land.
The new book Environment—Resources, Pollution & Society, edited by W. W. Murdoch, observes: “The open sea—an estimated 90 percent of the ocean—is considered a biological desert, contributing almost nothing to current world fishing and offering little potential for the future.” The majority of sea creatures live and are caught in the relatively shallow coastal waters. In fact, fish are concentrated in certain nearshore areas. Why?
Areas abundant with fish have a right combination of wind, current and slope of continental shelf that brings from the ocean depths water laden with nutrients from decomposed sea life. On reaching the levels of the ocean where sunlight penetrates, the “upwelling” nutrients result in the rapid proliferation of tiny floating plants and animals upon which fish feed. Thus the above-quoted source notes: “Upwelling areas form only about 0.1 percent of the ocean, but produce half of the world’s fish supply.”
Of what significance is the concentration of fish in small areas of the ocean and their scarcity elsewhere? It is as Fisheries Biologist William Ricker warned: The sea is not “a limitless reservoir of food energy.” And underseas explorer Jacques-Yves Cousteau warned, on returning from a world underseas exploration, that life in the oceans had decreased by 40 percent since 1950 due to overfishing and pollution.
So apparently man cannot count on conventional fishing methods to increase greatly his food supply. In fact, based on such reports as that of Cousteau, there is danger that less food will be available from the seas in the future.
Another Method
Yet some still feel that earth’s waters hold an answer to food shortage. They note that fishing fleets roam about looking for their prey, even as it was once common on land for men to hunt animals. But greater food productivity was realized when the emphasis shifted to raising land animals instead of hunting them. It is felt that a similar shift of emphasis could increase the productivity of the sea. The method of raising water creatures in captivity is called aquiculture (water farming), or mariculture (sea farming).
Aquiculture has recently caught the public fancy. But what are its prospects? Can creatures that live in the water be raised for food, even as cattle, swine and other land animals are? What has been done in this field? Is aquiculture an answer to relieving world food shortage?
An Old yet Productive Practice
Aquiculture is actually an old practice. As far back as 475 B.C.E. a treatise on raising fish was written in China by a Fan Li. Other peoples, including the ancient Greeks and Romans, also practiced the art.
In China aquiculture has been developed so that it is an important food source. Some 1.5 million metric tons [3,306,000,000 pounds] of carp and carplike fishes are produced there a year. That represents the major part of aquiculture’s annual world production of over 2 million metric tons.
The countryside of China is dotted with freshwater ponds in which carp are raised. The carp has been selectively bred to produce a fast-growing, fleshy fish with a minimum of scales. And the Chinese exercise care to prevent its reversion to the wild type. That this can quickly occur is shown by what happened when the carp was introduced to America in 1877, and was allowed to escape into rivers and lakes. It reverted to the bony, scaly, wild variety often found in waters used for game fishing.
Aquiculture is also practiced on a large scale in Indonesia, the Philippines and Taiwan, and quite extensively in northern Italy. Near the coasts of these countries hundreds of thousands of acres of brackish water ponds are maintained. Here milkfish (a tropical fish resembling a large herring) and gray mullets are raised. Since breeding of these fish in captivity is in the experimental stage, the young must still be collected along the shores and transferred to ponds to mature.
The productivity of these ponds makes the effort worth while. In the Philippines, for instance, the annual milkfish harvest yields some 42 million pounds, an average of about 500 pounds per acre. In Indonesia, where sewage is diverted into the ponds, the annual production sometimes exceeds 4,000 pounds per acre. These fish, however, need to be well cooked before they are eaten.
Catfish, Trout and Salmon
In the United States significant strides have been made in raising fish for food. Within the last decade catfish aquiculture has progressed from just a few farmers learning the art by trial and error to a booming industry. By 1970 there were 58,000 acres in ponds, principally in the Mississippi delta area. These ponds produced some 78 million pounds of catfish! That represents a yield of over 1,300 pounds per acre, far above the 300 to 500 pounds of beef an acre produced from good grazing land.
Trout and salmon are also important in aquiculture, especially rainbow trout. In Idaho’s Snake River valley a vast underground lake makes possible a rapid flow of water of the right temperature (58° F.) through fish ponds, which is ideal for trout raising. And by feeding the rainbows a special diet, fantastic annual yields of 400,000 pounds of fish per acre are obtained! Similar yields per acre have been achieved in Indonesia by confining carp in bamboo cages in a rapidly flowing stream that is rich in sewage.
Raising salmon involves more a “ranching” technique, rather than “farming.” Salmon hatch in rivers, migrate to the sea to mature, and, driven by instinct, return to their birthplace years later to spawn. By selective breeding and special feeding, very fast-growing, hearty salmon have been developed. Thus, instead of spending the usual four years in the ocean to mature, some of the new breed return to their birthplace in only a year. It is envisioned that large artificial runs of salmon will be produced that can be harvested on their return home after a year or so of pasturing at sea.
Raising Shellfish
The majority of shellfish, between 4 and 5 million metric tons a year, are taken from the sea by conventional fishing methods. But the farming of oysters, shrimp and other shellfish has also become common, with the Japanese taking a lead in the advances. For example, they pioneered the use of suspension cultures in oyster farming, a practice that is now spreading to the rest of the world.
After they hatch, the tiny oyster larvae swim about briefly in search of a suitable hard object on which to settle permanently to transform into adult form. In Japan was developed the practice of suspending wires from bamboo rafts into water up to nearly fifty feet in depth. Strung on these wires are clamshells that are spaced apart. Oyster larvae that attach themselves to the clamshells by the thousands of millions are, after a few weeks, culled by workers to the proper density. As the oysters grow, floats are added to the rafts to keep them from sinking under the increasing weight.
This suspension method has a number of advantages. It protects oysters from predators and silting on the sea bottom. And it also allows the oysters to feed on suspended food in the entire water column. Using this method the annual harvest in Japan’s Hiroshima Bay yields up to 50,000 pounds of oyster meat per acre!
Shellfish that move about, such as shrimp, are more difficult to raise. For centuries young shrimp in Far Eastern coastal waters have been captured and taken to brackish water ponds to mature to market size. However, in Japan true shrimp mariculture is practiced successfully on a commercial scale. There the shrimp are now grown under control from egg to market.
Egg-carrying females are caught and kept in carefully controlled tanks of seawater, where they release their eggs. Before reaching maturity the young undergo several larval stages during which they are kept in indoor heated water tanks. Later they are moved outside to ponds with arrangements for aeration and circulation to mature for market. There are a number of shrimp farms in Japan now, but most of these obtain the shrimp when they are young since they do not have the technical equipment to raise them from the egg.
True Mariculture in Infancy
As can be seen, aquiculture’s food production comes principally from fresh and brackish water ponds. Actual farming of the sea—true mariculture—has produced little. Most sea-farming efforts have been experimental, or they are only in the talking stage. The island-bound Japanese, who depend on the sea for 60 percent of their protein intake, are especially active in this research.
Enclosing sections of the sea to hold in fish is understandably no small project. However, in the Seto Inland Sea of Japan it has been done—sea farms are in operation. In one farm 180 acres are enclosed by wire fencing or netting at high water and fifteen acres at low water. The yellowtail fish, which grows to marketable size in about eight or nine months, are raised at high density in these enclosed farms.
Closing off a section of the sea is a real challenge. It has been envisioned that areas might be fenced off by laying a plastic hose on the sea floor, pierced with tiny holes and connected to an air supply. The rising air bubbles would serve as a curtain to keep unwanted sea life out, and the farm animals in.
It has also been noted that in the Pacific Ocean there are coral atolls, where rings of coral reef surround shallow lagoons. Japanese scientists have proposed raising tuna—a fish that may reach several hundred pounds—in such closed-off atolls.
Another avenue of investigation has been the fertilizing of water to sustain fish. In one experiment a 3-1/2-inch plastic pipe was extended nearly a mile deep off St. Croix in the Virgin Islands. The cold, nutrient-rich water pumped into pools on shore soon teemed with tiny plant life, becoming ideal for raising fish. One scientist proposed a seagoing dredge that would bring up nutrients from the depths and distribute them near the surface. Then the fish that might thrive in the area due to the artificial “upwelling” could be harvested.
In Scotland experimental success in mariculture has been achieved in using the warm water discharge of an atomic power plant. By raising the water temperature of a closed-off section of the sea both the metabolism rate and appetite of the fish—in this case, sole and plaice—were increased, greatly speeding their growth. However, in commenting on this successful experiment Sea Frontiers magazine interestingly observed:
“‘Farming the sea’ is a phrase often seen, as if this were an easy extension of farming the land. In fact at the present time problems are more common than produce, and the commercial rearing of even a single species represents a tremendous effort.” Thus one is reminded that mariculture is yet in its infancy.
An Answer to Food Shortage?
However, the need for more food is immediate, since already many of mankind are starving. Can farming the seas be developed to fill that need?
Indications are that it cannot. As Bio-Science magazine observed: “It is urgent to say at this point that the immediate return from mariculture will probably contribute very little to relief from hunger of the undernourished peoples of the world. It is unlikely that the caloric requirements of the hungry peoples can ever be met from the sea. The contribution to the immediate alleviation of protein hunger will at best be small.”
The best prospects for water farming appear to be inland, where at present it is most productive. This is especially true in view of the threat that pollution may ruin the sea as a safe source of food.
No doubt, in the future much more will be done to develop the art of aquiculture, and many persons will be benefited. But it cannot be depended on to solve man’s critical food shortage.