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Under international pressure, Chile introduced strict new regulations in January. But the problems surrounding fish farming are complex, and some are only dimly understood. Daniel Pauly, 55, a professor of fisheries science at the University of British Columbia, has calculated that it takes 2 to 5 lbs. of anchovies, sardines, menhaden and the other oily fish that comprise fish meal to produce 1 lb. of farmed salmon, which he says makes no sense in a world trying to increase the amount of available protein. Kentucky State University biologist James Tidwell, 47, a former president of the World Aquaculture Society, points out, however, that wild salmon are bigger eaters than that consuming at least 10 lbs. of fish to add 1 lb. in weight and argues that harvesting large amounts of short-lived species like menhaden is no more harmful than mowing the lawn. "Fish-meal fish are nature's forage," he says. "Cropping them merely increases their productivity."
Disease is always a problem when fish are raised in close quarters. After a 1999 outbreak of infectious salmon anemia in fish farms in Scotland, all the farm-grown fish within 25 miles were slaughtered. A similar anemia outbreak in Maine two years ago led to the destruction of more than 2.5 million fish and to federal insurance payouts totaling $16 million. "The more aquaculture there is," warns Callum Roberts, senior lecturer in marine conservation at the University of York in England, "the more disease there will be."
Some of the antibiotics that fish farmers give their stock to minimize disease pass easily into the surrounding environment, and some are highly toxic. Last year traces of the banned drug nitrofuran, which is dangerous to humans, were found by European Union inspectors in shrimp from Myanmar, Thailand and Vietnam. According to Wang Sihe, an expert with the Jiangsu Seawater Fisheries Research Institute, Chinese shrimp farms have mixed fish food with antibiotics and dumped it into fish ponds. Chloramphenicol, an antibiotic that can cause fatal anemia in humans, has also been used.
The fetid water that runs off shrimp farms is particularly damaging to the environment. Thailand, with 25,000 coastal shrimp farms, is the world's largest exporter of shrimp--$3 billion worth in 2001 alone. Through last June, Thailand accounted for 28% of the shrimp imported into the U.S. But this commerce is costly. Long strips of coastline south of Bangkok now look like powdery gray moonscapes. Shrimp farms can raise the salinity of the surrounding soil and water, poisoning the land for agriculture. Some flush their effluent into the sea, killing mangrove trees. Shrimp farming is also practiced in Brazil, India and Ecuador, and in the U.S. in Florida, South Carolina and Texas.
Parasite infestation is another chronic problem of high-density seafood farms. One of the most damaging organisms is the sea louse, which breeds by the millions in the vicinity of captive salmon. In 1989 Peter Mantle, who owns a wild salmon and sea-trout sport fishery in Delphi on the west coast of Ireland, discovered that young trout returning to his river from the ocean were covered with lice that were boring through the trouts' skin and feasting on their flesh. The sea lice were breeding near newly installed salmon farms in the inlet fed by his river. By the time the salmon farmers started dosing their pens with anti-sea-lice chemicals, the sea-trout fisheries of the west of Ireland were effectively dead. "Sea-trout fishing was sustainable and eco-friendly," says Mantle, "but the salmon farms killed it off within a decade."
In the long run, wild-fish stocks may face an even greater threat from captive fish escaping and competing with or consuming native fish, or cross-breeding with them and diluting the genes that have helped them survive. Fish escapes are common: nets are ripped open by predators or storms, fish in ponds get swept into channels by rainfall, others are released accidentally during transport. Bighead and silver carp that were introduced to China's plateau lakes in the 1950s have cleared those waters of whole species of indigenous fish. And Asian carp, which were introduced in Mississippi Delta catfish ponds to control parasites, escaped in the early 1990s and have migrated up the Mississippi and Illinois rivers to within 25 miles of Lake Michigan, threatening native fish with their voracious feeding habits.