But environmentalists say the aquaculture boom is masking problems with the world's fisheries and wreaking new ecological damage.
Gerry Leape, vice president for marine conservation at the Washington-based National Environmental Trust, said U.S. officials see that "the oceans are in crisis, and what's their response? To allow the enormous expansion of this industry that's proven to have a negative environmental impact."
The Aqua Leader fish harvester sucks salmon through a vacuum hose off New Brunswick's Lime Kiln Bay.
(Courtesy Of Cooke Aquaculture)
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Much of the controversy has focused on the fish feces and excess food that build up beneath the floating net pens and can form bacteria mats on the sea floor that harm marine life. Many scientists say these problems can be reversed by rotating the pens and allowing some to lie fallow, and most growers now use closer monitoring to reduce excess feeding. But salmon waste off the British Columbia coast still releases as much excess nitrogen as sewage from a city of 250,000, according to some estimates.
After environmentalists charged that two Maine salmon growers had violated Clean Water Act requirements, a federal judge ruled in 2003 that the companies had to leave nearly all their sites fallow for two years after they harvested their remaining fish. That improved local water quality, but industry experts say the move hurt the viability of fish farming in the state.
Many commercial fishermen are more worried about two other factors: the spread of disease that comes when animals are crowded together and the use of chemicals to combat these illnesses. In Maine, Canada and elsewhere, farmed fish have passed sea lice, which eat salmon flesh, to their wild counterparts. Infectious salmon anemia, a lethal disease first discovered in Norway in 1984, has spread globally, prompting one Maine fish farm to kill more than 1.5 million fish in 2002 to try to contain the infection.
Escaped salmon, which compete for natural resources with other fish and can sometimes interbreed with their wild counterparts, pose another potential risk. Fred Whoriskey, who heads the research staff at the Atlantic Salmon Federation and works on saving the few thousand wild salmon that still live in North American waters, found more than eight times as many escaped fish farm salmon as wild salmon in New Brunswick's Magaguadavic River last year.
Mitchell Shapson, a lawyer at the San Francisco-based Institute for Fisheries Resources who represents wild-catch fishermen, said his clients resent aquaculture's impact on their hunting grounds.
"If you destroy the environment and you destroy the wild fish, there won't be anything left to fish," he said.
Fish growers say they have made progress on several fronts: According to industry officials, the number of escaped Atlantic salmon in British Columbia dropped from 89,000 in 1998 to 2,500 last year.
"When we do something wrong it comes back to bite us first," said Belle, the Maine industry spokesman. "It hurts us in our pocketbooks."
The recent debate about health risks associated with farm salmon -- one 2004 study published in the journal Science concluded that raised salmon had such elevated levels of PCBs, dioxin and other cancer-causing contaminants that consumers should limit themselves to one eight-ounce portion a month -- has also made aquaculture controversial. Industry officials counter that the health benefits of eating salmon, rich in omega-3, far outweigh any cancer risks, and they have conducted recent studies showing PCB levels in farm salmon that are comparable to those in wild fish.
Not all aquaculture is environmentally harmful. Farming clams, oysters and scallops reduces nutrient pollution that can deplete the ocean's oxygen and cause harmful algae blooms, and raising shrimp can be less environmentally damaging than trawling for them, which can destroy coral reefs and enmesh other fish. Researchers are experimenting with new, more expensive techniques on land, and farther offshore, to mitigate fish farming's impact.
In West Virginia, the Conservation Fund's Freshwater Institute has developed land-based farms that recirculate water to contain pollution, disease risk and potential escapers. The plant boasts a massive 40,000-gallon tank that holds 60,000 rainbow trout, which are collected by a plastic grate once they are large enough to go to market. Ninety-eight percent of the tank's water is reused after specialized treatment.
New Brunswick's Cooke and other companies already use recirculated water in their onshore hatcheries.
At the other end of the spectrum, Hogarth and other U.S. officials are pushing to put aquaculture operations farther offshore, on the theory that tides will disperse nutrients better and that submerging pens deeper underwater will protect them from storms and sea traffic. Initial results from offshore research facilities are promising: Richard Langan, who directs the University of New Hampshire's Open Ocean Aquaculture project, said that in five years the venture has not had a single escaped cod, halibut or haddock from its three galvanized steel cages positioned six miles off the coast, and researchers have not detected any adverse environmental impacts.
The administration plans to announce legislation to regulate offshore fish farms early this year, but advocates such as Ellen Athas, director of the Clean Oceans program for the Ocean Conservancy, are worried the bill does not set clear enough standards and rules. "If we don't get a grip on where things are going, we are going to have an absolute mess out there," she said.
But for fishing communities such as Eastport, Maine, impoverished by the decline of Atlantic fisheries, aquaculture offers a tempting solution. The city was once a thriving shipping center and sardine cannery town, but its population has dropped by two-thirds in the past 100 years. City Council member Gary Biss saw some of aquaculture's initial excesses as a company diver in the 1980s, but he said the industry has improved its record and deserves public support.
"The world needs the food," Biss said. "There's a crying need for it. It has to be somewhere. It would be nice if it were here."
