National Geographic : 2014 Jun
110 national geographic • june 2014 could get out of fish meal today if it wanted to.” Replacing fish oil remains trickier, because it carries those prized omega-3 fatty acids. In the sea they’re made by algae, then passed up the food chain, accumulating in higher concen- trations along the way. Some feed companies are already extracting omega-3s directly from algae—the process used to make omega-3 for eggs and orange juice. That has the added benefit of reducing the DDT, PCBs, and dioxins that can also accumulate in farmed fish. An even quicker fix, Stanford’s Rosamond Naylor says, would be to genetically modify canola oil to produce high levels of omega-3s. Figuring out what to feed farmed fish may ul- timately be more important for the planet than the question of where to farm them. “The whole concept of moving into offshore waters and on land isn’t because we’ve run out of space in the coastal zone,” says Stephen Cross of the Univer- sity of Victoria in British Columbia, who was an environmental consultant to the aquaculture industry for decades. Though pollution from coastal salmon farms gave the whole industry a black eye, he says, these days even salmon farms are producing 10 to 15 times the fish they did in the 1980s and 1990s with a fraction of the pollu- tion. In a remote corner of Vancouver Island he’s trying something new and even less damaging. His inspiration comes from ancient China. More than a thousand years ago, during the Tang dynasty, Chinese farmers developed an intricate polyculture of carp, pigs, ducks, and vegetables on their small family farms, using the manure from ducks and pigs to fertilize the pond algae grazed by the carp. Carp were later added to flooded paddies, where the omnivorous fish gobbled up insect pests and weeds and fertilized the rice be- fore becoming food themselves. Such carp-paddy polyculture became a mainstay of China’s tradi- tional fish-and-rice diet, sustaining millions of Chinese for centuries. It’s still used on more than cobia a good farm animal is fueled in the wild by a diet of smaller fish or crustaceans, which pro- vide the perfect blend of nutrients—including the omega-3 fatty acids that cardiologists love. Cobia farmers such as O’Hanlon feed their fish pellets containing up to 25 percent fish meal and 5 percent fish oil, with the remainder mostly grain- based nutrients. The meal and oil come from for- age fish like sardines and anchovies, which school in huge shoals off the Pacific coast of South Amer- ica. These forage fisheries are among the largest in the world but are prone to spectacular collapses. Aquaculture’s share of the forage-fish catch has nearly doubled since 2000. It now gobbles up nearly 70 percent of the global fish meal sup- ply and almost 90 percent of the world’s fish oil. So hot is the market that many countries are sending ships to Antarctica to harvest more than 200,000 tons a year of tiny krill—a major food source for penguins, seals, and whales. Though much of the krill ends up in pharmaceuticals and other products, to critics of aquaculture the idea of vacuuming up the bottom of the food chain in order to churn out slabs of relatively cheap protein sounds like ecological insanity. In their defense, fish farmers have been get- ting more efficient, farming omnivorous fish like tilapia and using feeds that contain soybeans and other grains; salmon feed these days is typically no more than 10 percent fish meal. The amount of forage fish used per pound of output has fallen by roughly 80 percent from what it was 15 years ago. It could fall a lot further, says Rick Barrows, who has been developing fish feeds at his U.S. Department of Agriculture lab in Bozeman, Mon- tana, for the past three decades. “Fish don’t require fish meal,” says Barrows. “ They require nutri- ents. We’ve been feeding mostly vegetarian diets to rainbow trout for 12 years now. Aquaculture Salmon farms gave the industry a black eye. But these days even salmon farms are producing 10 to 15 times the fish they did in the 1980s and 1990s with a fraction of the pollution. Contributing writer Joel K. Bourne, Jr., is working on a book about food. Brian Skerry photographed the bluefin tuna for our March issue.