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[经济学人] [2008.12.30]第六篇之耕作海洋(Come, friends, and plough the sea)









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发表于 2010-4-29 00:27 | 显示全部楼层 |阅读模式
A special report on the sea

Come, friends, and plough the sea

Dec 30th 2008
From The Economist print edition

But make sure farmed fish are veggies

“Will you walk a little faster?” said a
whiting to a snail,
“There's a porpoise close behind us, and
he's treading on my tail.”

Lewis Carroll
FOR most of man’s existence he has been a hunter-gatherer. These days, however, it is as a farmer that he harvests almost all his food from the land. Now he has started farming the sea, too. The world produced 48m tonnes of farmed fish in 2005, worth $71 billion. That was 34% of the total, a proportion that is likely to rise to half by 2010. A huge variety of fish, including cod, crayfish, bream, halibut, mussels, salmon, sea bass and sturgeon, are all farmed, providing jobs and food for people all over the world.
Unfortunately, fish farming is still in its infancy and in some places may do more harm than good. In Indonesia, Thailand, Vietnam and other parts of Asia, huge swathes of coastline have been denuded of trees to make way for ponds and pens. Many fish farms create pollution, too. Even if the water in which the fish are reared starts out fresh, the build-up of faeces and uneaten food soon makes it foul. The mix is made even nastier by the pesticides and antibiotics needed to keep the crop alive. And to cap it all, aquaculture produces CO2 and gobbles up energy.
China, which produces about 70% of the world’s farmed fish, has been a notable offender in creating such pollution. Many of its fish have been found to contain heavy metals and toxic chemicals. But China is not alone. When salmon farming first started in Europe, the fish often became infested with lice, which then spread to wild fish. The drugs to treat them contributed to the pollution of the waters, already contaminated by the growth hormones and antibiotics added to the food.
Similar problems still arise elsewhere. Millions of fish were killed last year when a virus called infectious salmon anaemia swept through Chile’s salmon farms. Many blamed the outbreak on intensive farming. Farmed fish are also prone to parasites, one of which, Gyrodactylus salaris, has infected about 10% of Norway’s rivers, wiping out the wild salmon. Farmed fish also do damage when they escape, as many do. Sometimes the escaped fish interbreed with wild fish to the detriment of the local stock. Sometimes they eat the young of their rivals. Always they compete for food.
The solutions to these problems are often known, if not applied. They usually involve fewer farms, colourings and pesticides, and cleaner water. But some difficulties are more complicated.
Cod’s head for salmon’s tail

Some fish, such as groupers and eels, do not breed in captivity. They must be reared from fish caught in the wild, whose stocks are thereby reduced. And most of the fish that people like to eat are predators, which means they must themselves be fed fish. This is not an efficient business. It takes at least three kilos of fish meal to add one kilo to the weight of a farmed salmon. Most of this meal is made of ground-up anchovies, menhaden or sardines. Such forage fish already account for nearly a fifth of the world’s total annual catch; another fifth goes to feed pigs and poultry. Increasingly, as these small and middle-sized fish run out, smaller and hitherto commercially worthless ones are scooped up in fine-meshed nets. With them are quantities of tiddlers that, were they to survive, would grow into bigger, commercially valuable fish.
They might be ecologically valuable too. The striking drop in numbers round British coasts of such seabirds as arctic terns, kittiwakes, guillemots and puffins is probably a result of the disappearance of sand eels. These have either fled north to stay cool or been fished to the last elver before being turned into salmon feed.
Perhaps the most grotesque form of fish farming is the ranching of bluefin tuna, a delicacy that may sell for as much as $860 a kilo. Bluefins are sensitive creatures that hate being cooped up so much that, if confined, they tend to throw themselves against their cages and break their necks. Australian “ranchers” have now adopted a technique that involves catching young bluefins, enveloping them in a huge net and dragging it slowly round the south seas for months while feeding them pilchards imported from west Africa.
If fish are to be farmed in ever greater numbers, most had better be plant-eaters. Even better, from an environmental point of view, are molluscs such as mussels, clams and oysters. These need no feeding, thriving on plankton alone. They may even clean the water they live in. The main damage associated with farming shellfish is caused by harvesting them with dredges, which ruin the seabed. Fortunately, they can be gathered by divers.

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