American Scientist

Traditionally, the first of May is a day of festivity—a time to rejoice over the springtime return to abundance. This past May Day, however, many people who normally remain in close touch with nature were in no mood to celebrate: Because of historically low returns, the U.S. Secretary of Commerce officially declared the West Coast salmon fishery to have failed. Fishers of the region have thus had to face newly issued regulations that eliminate or severely limit the take, both recreational and commercial, of this popular, pink-fleshed fish.

As distressing as it is, this development can't be considered a surprise. Indeed, the collapse of the West Coast salmon fishery reflects a long-term global trend. A type of fish that used to teem in the rivers of California and in pre-industrial New England and Europe, to name some examples, has fallen into severe decline in all these places, as it has in many other parts of the world.

Finding reasons is not difficult. One obvious candidate is the presence of dams, which block the fish when they return from the sea to spawn in freshwater streams. Other factors include the warming of ocean and river waters, pollution, overfishing—even the loss of beavers, whose mud-and-twig dams had once provided juvenile salmon with abundant shelter from predators.

The recognition that salmon are in trouble itself has a long history. In the 19th century, artificial fertilization and incubation of salmon eggs were used to help give these fish a boost in Europe and North America. A century later, these techniques evolved into full-blown farming operations, in which salmon are raised to adulthood in floating "net pens" and then harvested for consumption. Norway pioneered this approach in the 1960s, and it has since spread to other regions, including Newfoundland, British Columbia and Chile.

One might guess that salmon farming would take pressure off wild stocks, but, in fact, the opposite appears to have happened. One reason may be the introduction of diseases from farmed fish to wild salmon passing close to net pens. Another may be the genetic dilution that arises when escapees from the farms mix with their wild (and more fit) cousins.

But with so many possible causes for the declines, it has been hard to judge whether salmon aquaculture is indeed as detrimental as feared. A paper published in PLOS Biology this past February helps to clear up the uncertainty. Working at Dalhousie University, Jennifer S. Ford and the late Ransom A. Myers amassed information about declining salmon populations around the world—both ones located near salmon farms and ones separated from these operations. What these authors found was that wild salmon exposed to the farms have experienced much sharper declines in their numbers.

Ford, who now works for the Ecology Action Centre in Halifax, stresses that salmon farming is not the only problem. "Absolutely without a doubt, there are all sorts of things affecting salmon," she says. And she accepts that this effect of salmon aquaculture isn't universal. But even if the circumstances in some locales are different, she notes, finding a clear trend in a global analysis makes the result much more compelling than any one case study could ever be. "What makes it robust," Ford says, "is that we've done it in different places."

John P. Volpe, who heads the seafood ecology group at the University of Victoria, agrees. He notes that the data Ford and Myers used for their global study are "rather thin," but he's nevertheless swayed because "you find a similar signal no matter where you look." And to Volpe, the correlation between farming and sharp wild-salmon declines just makes sense, because aquaculture breeds problems such as "sea lice" (a pathogenic crustacean), which can then harm the wild fish. Indeed, he says it's a conclusion that any 10th-grade science student would have an easy time reaching: "If you take a million fish and put them in a net pen, you're going to amplify pathogens and diseases."

Asked about solutions, Volpe doesn’t hesitate to venture his opinion: "Closed containment," he says, referring to schemes that isolate the farmed fish, and any parasites and diseases they harbor, from wild ones. Volpe points out that the technology for farming salmon this way has been available for more than a decade; it just makes farming more expensive. The real problem, as far a Volpe is concerned, is that these days people expect salmon to be cheap and plentiful all the time.

So perhaps the solution should not just involve technical improvements in how the farming is done or the tightening of fisheries and environmental regulations. What may be needed every bit as much is a change in mindset. Rather than seeing salmon as an inexpensive staple, consumers should begin once again to view it as a delicacy, one that is perhaps only affordable when it is in season. For many, eating salmon would then become, to use Volpe's words, "almost a commune with nature."