Environmental Case Study a Blue Revolution

Environmental Case Study A Blue Revolution

Seafood, including fin fish, shellfish, and crustaceans, is prized by many people, and it provides the main animal protein source for nearly 1 billion residents of developing countries. Populations of wild fish are declining, however, in many parts of the world. The UN Food and Agriculture Organization (FAO) estimates that three-quarters of all marine stocks are being exploited at or beyond sustainable yields. Furthermore, indiscriminate and destructive harvest techniques are destroying habitat and disrupting marine communities in ways that may make it difficult to rebuild populations. Canadian fisheries experts report that only 10 percent of large predators such as sharks, marlin, tuna, and swordfish remain in the ocean. In the North Atlantic, once immense groundfish populations (cod, halibut, flounder, and skate) have been exploited to near extinction.

How can we replace this valuable protein source? Aquaculture, or fish farming, which now produces about one-third of the seafood eaten by humans every year, is the fastest growing sector of our food producing system. Economist Lester Brown predicts that fish farms may be the feedlots of the future. Beef production, he reports, which now provides about 55 million metric tons per year, has grown by about half over the past 30 years. Aquaculture, in that same time, has grown nearly tenfold, from about 3 million metric tons per year to more than 30 million metric tons. If these trends continue, fish farming may soon overtake cattle ranching as the largest source of animal protein in the human diet. Some marine biologists expect this “blue revolution” in aquaculture to be as important as the “green revolution” in terrestrial crops that greatly reduced chronic hunger and malnutrition worldwide over the past 30 years.

Many seafood species can be raised in captivity more efficiently than can birds or mammals. It takes about 7 kg of feed, for example, to produce 1 kg of beef. By contrast, only 1.6 kg of feed will yield 1 kg gain in catfish. Although at least 220 species of aquatic organisms are raised for food, a dozen or so dominate world output. China, where fish farming began more than 3,000 years ago, is by far the world leader in this field, producing 71 percent of the total volume and 50 percent of the total value of all aquaculture every year. About 6.5 million ha of Chinese ponds, lakes, reservoirs, and rice paddies are used for seafood cultivation. Most of China’s aquaculture is integrated with agriculture, enabling farmers to use agricultural wastes, such as rice straw and pig manure, to fertilize ponds.

Not all fish farming, however, is environmentally or socially benign. Much of the production, especially that destined for markets in richer countries, is in high-value carnivorous marine species such as salmon, cod, and shrimp. Huge volumes of wild-caught fish such as anchovies are processed into fish meal and fish oil to feed these carnivores, which may take more protein to produce a kilogram of edible product than do cattle, hogs, or chickens. Fish meal can be contaminated with PCBs and other dioxin-like compounds from the fish oil it contains. According to the Environmental Working Group, farmed salmon are likely the most PCB-contaminated protein source in the U.S. food supply. In samples from U.S. grocery stores, farmed salmon were found to have 16 times as much PCBs as wild fish and 4 times as much as beef. Fish meal production also depletes food for wild marine species such as cod, seals, and seabirds. Furthermore, many fish farms depend on wild-caught rather than hatchery-reared young to stock captive-rearing operations. This practice can severely deplete natural communities.

Fish feces and uneaten food falling from net pens can seriously pollute near-shore waters. Dense populations of captive species in ponds or pens often require use of antibiotics and disinfectants, which also can contaminate surrounding ecosystems if they are discharged into surface waters. Non-native species and genetically modified organisms can escape from captivity to hybridize with or outcompete native wild fish. And destruction of hundreds of thousands of hectares of mangrove forests and coastal wetlands—especially for shrimp ponds—threatens nurseries important for many marine species. Fish ponds created on former agricultural land can have high levels of pesticides, PCBs, and other toxic contaminants.

Environmental Case Study A Blue Revolution

Still, there is great promise for ecologically, socially, and economically sustainable fish farming to produce valuable, high-quality protein to feed growing human populations.