The detection of infectious salmon anemia, a lethal virus, in two juvenile wild sockeye salmon in British Columbia has reinvigorated a long-running debate about the sustainability of the aquaculture industry, particularly salmon farms.
Worldwide, the majority of salmon farms are situated in the ocean, with a net the only barrier between the farmed fish and the wild ones. Such pens produce thousands of tons of fish each year, said Gary Marty, a fish pathologist for the Ministry of Agriculture in British Columbia.
Some scientists and environmentalists are calling for moving the salmon farms to inland freshwater pens to protect the ocean environment.
The two wild sockeye with the virus were discovered along the province’s central coast. Some biologists suspect that the ailment could have spread from the saltwater salmon farms.
“This form of fish farming has lots of opponents,” said Daniel Pauly, a fisheries biologist at the University of British Columbia.
Glen Spain, the Northwest regional director for the Pacific Coast Federation of Fishermen’s Associations, suggests that onshore farms would diminish the need for “these massive undertakings in the wild.”
For now, though, there is no indication that moving farms onto land is a viable plan. “That’s probably not a standard thing we’d do, moving onto land,” Dr. Marty said. For starters, such a move would cost $1 billion to $2 billion, he said.
Although moving the farms would protect wild fish, diseases can still develop inland, Rosamond Naylor, the director of the Center on Food Security and the Environment at Stanford University, noted. She also points out that an inland system is more costly to operate and consumes more energy as clean water is replenished.
“I don’t think you can reach the same scale of production without increasing consumer prices quite a bit,” she said.
Still, open-water salmon farming has numerous negative environmental consequences because so many factors are harder to manage, Dr. Pauly said. Infectious salmon anemia is only the meltdown point amid a host of other problems, he added.
Sea lice, the parasitic crustaceans that feed on live fish tissues, are prolific in the ocean farms and can jump from farmed fish to wild ones that pass by the enclosures. Chemicals are used to treat the lice, and the parasites may quickly develop resistance to them. Sediment on the bottom of aquaculture ponds creates a mini dead zone.
High levels of antibiotics are sometimes used to treat bacterial diseases, and farmed fish that escape may then interbreed with wild fish and compete with them for resources. An estimated 3 to 5 percent of all farmed fish escape their pens, usually through events like storms or during common procedures like cleaning pens or transporting the fish
It’s also easier for companies to avoid regulations when operating out in the ocean, said Mr. Spain of the fishermen’s federation, “and that’s a recipe for disaster.”
Norwegian-owned Marine Harvest, the world’s largest salmon farming company, which owns 55 percent of the salmon farms in British Columbia, has been charged with four counts of illegal possession of wild Canadian salmon and herring.
In an e-mail, Ian Roberts, a spokesman for Marine Harvest, confirmed that the company would plead guilty to the charges.
Since 2001, the company has been fined more than $125,500 in British Columbia, Scotland, and Chile for other violations including pollution, breaching water-use licenses and lax health and safety standards for workers.
Some experts advocate a total ban on salmon farming, on land or at sea.
“Aquaculture of carnivores is hopeless and extremely wasteful,” said Dr. Pauly, who supports such a ban. The farmed fish are fed with species that people could consume, he said, so it ends up contributing to human demand for the wild stocks of other species.
For every pound of salmon produced, five pounds of wild fish are needed, usually in the form of anchovies, sardines, or mackerel. “It’s like feeding tigers a ton of livestock to get tiger meat,” says Alex Muñoz Wilson, the vice president in Chile for the nonprofit ocean conservation group Oceana.
Many of these feed fish are species that people could eat, Mr. Muñoz said. A decade ago in Chile, the annual mackerel catch was around four million tons, he said. Today, only about 200,000 tons are harvested annually, he said, although the salmon farms are only partly responsible.
“I think in the long run, salmon aquaculture creates more problems than benefits,” Mr. Muñoz said.
On the other hand, said Ray Hilborn, a professor of aquatic and fishery sciences at the University of Washington, salmon farming “looks pretty good compared to livestock farming.”
About 30 to 40 million tons of fish are caught each year that are unmarketable for humans, he says, and much of that surplus now goes to salmon. He says that salmon aquaculture takes up much less space than livestock farms: Norway’s annual 500,000 tons of salmon production covers an area about the size of the Oslo airport, he noted.
“You can’t look at the environmental impacts of salmon farming in isolation,” Dr. Hilborn said.
