It turns out that farm-raised salmon, touted as inexpensive fare for heart-healthy diets, may not be such a good mealtime addition after all. On Jan. 9, the journal Science published an article detailing an exhaustive analysis of some 700 farm-raised salmon. Most had levels of dioxin—cancer-causing chemicals that are the byproduct of various industrial processes—as much as 11 times higher than those found in wild salmon. The best explanation for the big dose of dioxin is that farm-raised fish are eating badly themselves—food pellets mostly derived from ground-up fish. A less-diverse diet than wild salmon eat, it allows concentrations of chemicals to pass easily to farmed salmon.
There's a certain "So what?" element to all this. The tested fish were not skinned or cooked, two steps that greatly reduce dioxin. And, as many food experts have pointed out, the added risk of the dioxin is probably more than compensated for by the benefits of eating salmon. That's because salmon, an oily fish, is rich in omega-3 fatty acids, a substance that almost certainly helps protect against heart disease and may also reduce the risk of cancer and Alzheimer's. Salmon—even farm-raised salmon—also are low in mercury, a chemical prone to show up in tuna and other fish. The average American is far more apt to croak from heart disease due to too many Big Macs than from cancer caused by a few helpings of ranch-raised salmon.
That doesn't let farmed salmon off the hook, though. Why? Because the aquaculture industry that creates them also creates plenty of other problems. Farm-raised salmon were largely unheard of 20 years ago. But after getting their start in northern Europe and then spreading to places such as Chile and British Columbia, Canada, "salmon farms" grew rapidly. Today they account for some 60 percent of salmon worldwide—1.4 million metric tons in 2002, which is a lot of salmon steaks. The abundance of farmed salmon has helped make a fish that once was largely a luxury item (or an expensive canned fish) into a commonplace meal in homes and restaurants.
But raising cattle or hogs causes problems—pollution, trampled rangelands, increased risk of spreading disease. Farmed salmon bring their own set of troubles in their wake. For starters, aquaculture is a dirty industry. As many as 600,000 salmon may be raised in a single net-enclosed pen—itself usually installed in a protected fjord or inlet. Although progressive farmers rotate "crops" of fish between pens, the sea floor under the enclosed salmon becomes covered with fish excrement and uneaten food, creating a dead zone where nothing can live or grow. By some estimates, the salmon farms in British Columbia pump out as much fish feces as the human equivalent from a city of 500,000.
Those concentrations of fish, meanwhile, are happy hunting grounds for diseases and parasites. Although a link hasn't been clearly established, many fish-farming foes believe that swarms of sea lice—a tiny marine parasite that eats the skin and mucous membranes of salmon—proliferate in crowded fish pens then migrate out to infect wild fish. A few sea lice pose no threat to a wild salmon (indeed, the wild fish probably are the ones that infected the farmed ones). But in large numbers, sea lice can kill or weaken wild salmon.
Then there's the issue of what kinds of salmon are raised. Because it got its start in northern Europe—Norway remains the world production leader—salmon farmers adopted the Atlantic salmon as their preferred species. The fish tasted good, grew rapidly, and were a convenient size for the retail market. But now salmon farmers in the Pacific region are raising Atlantic salmon, which poses another ecological danger. It's not at all uncommon for marauding sea lions to break through salmon nets for an easy meal, allowing thousands or even millions of farm-raised fish to escape.
These fish have little in common with wild peers in any ocean. They're dumb as rocks—even by piscine standards—weak, and prone to disease. Genetically, they're the product of intense interbreeding. Should they ever make it with wild salmon, the results could be devastating for the wild fish, many of which are endangered or threatened species. "It's just crazy to let people raise farmed fish of the same species if you have wild stocks nearby that you're concerned about," says Ray Hilborn, a fisheries biologist with the University of Washington. "If they interbreed, it's a total disaster for the wild stocks." Coincidentally, the United Nations has declared that the introduction of alien species is, after habitat loss, the greatest threat to global biodiversity. Yet salmon farmers still use Atlantic salmon in Pacific pens.
Finally, overproduction in what started as a mom-and-pop business but now is largely controlled by giant conglomerates has led to a near collapse in salmon prices. It's good for consumers but a catastrophe for those fishers still plying an honest trade catching wild salmon. Fishers in Alaska, for instance, have seen prices for some salmon species plummet to as low as 45 cents a pound, compared with $2 per pound a decade ago. That's putting them out of business, not only forcing them to work harder and take bigger risks to make a living, but putting more pressure on wild salmon stocks as fishers try to make up low prices through volume. In some areas, such as Alaska's Bristol Bay area, the collapse of the salmon-fishing industry has led to growing calls for oil-drilling in the environmentally sensitive area in an effort to create new jobs. And we all know what that can lead to. Alaska's Prince William Sound has yet to recover from the 1989 oil spill from the Exxon Valdez.
Aquaculture doesn't have to be a bad deal. Catfish and other species are raised successfully and fairly cleanly by fish farmers. (Asian shrimp farms, though, may be even worse than salmon farms.) Good aquaculturalists carefully monitor water quality, use minimal antibiotics and pesticides to keep fish healthy, and ideally raise their crop in closed systems—not in pens stuck near the open ocean. (And they push for better quality pellets to feed their fish, too.) If the current scare inspires consumers to make it clear they want wild salmon, not farm-raised fish, then perhaps the market will help rein in what has become a marine menace.