Fishing for salmon answers | Science Matters | David Suzuki Foundation
Photo: Fishing for salmon answers

The best solution would be to raise salmon in closed tanks that keep the farmed fish separate from the wild fish and their environments (Credit: esc.ape(d) via Flickr).

By David Suzuki with Faisal Moola

Most of our food, whether plant or animal, comes from farms. A notable exception is fish and seafood, much of which is caught from wild ocean stocks. That's starting to change, though, as aquaculture plays an increasingly important role in the global food supply.

In many respects, that's good news, especially when wild fisheries are being harvested at or beyond a sustainable limit, and pollution and global warming, among other threats, are decimating wild fish stocks. When the aquaculture practices themselves start harming the wild fish, though, we must question whether or not the costs of the way we are farming outweigh the benefits.

Many aquaculture operations are environmentally sound, especially those that separate farmed fish from wild fish, such as the contained tanks and pond systems used to farm species such as tilapia and turbot. As well, many types of shellfish are farmed in ways that do not harm the environment.

Yes, you heard me right: some types of aquaculture are okay. And yes, I eat some farmed seafood.

But current salmon-farming practices are a different story. We've seen a lot of headlines lately about the damage done by salmon farms, here in Canada and in other parts of the world. The scientific evidence is strong and growing, for example, that sea lice from salmon farms in B.C. are causing severe damage to wild salmon stocks.

Sea lice are natural parasites that feed on salmon, and are especially harmful to juvenile salmon, which don't yet have scales to protect them and which aren't normally exposed to sea lice in large concentrations. Sea lice multiply on salmon farms and attach themselves to juvenile salmon as they pass the farms on their way out to sea. Using drugs to control the lice isn't the answer, as the drugs come with their own environmental risks. And at best it is only a short-term solution as sea lice are already developing resistance to the main drugs used to control them.

Research has demonstrated similar situations in other salmon-farming regions like Scotland, Ireland, Norway, and Chile. Here in North America, a series of peer-reviewed scientific studies published in reputable journals such as Science and the Proceedings of the National Academies of Science has shown that sea lice can cause serious harm to wild salmon, including putting some stocks of pink and chum salmon at risk of extinction.

Wild salmon do not need additional threats to their survival. To put the issue in perspective, the West Coast of Vancouver Island once boasted 1,200 stocks. Now, some 718 — more than half — are extinct, at moderate risk of extinction, or considered stocks of special concern. At least 142 Pacific salmon populations have vanished forever.

Given the scientific evidence and the social, economic, and biological value of salmon, it is reasonable to expect change in the way things are done. Unfortunately, some people argue that the lack of 100 per cent proof means nothing should change. But scientific research rarely gives us such smoking guns. Nature is just too complex to even expect such a result. Science is a process of demonstrating the weight of evidence. Studies build on each other, eliminate alternative explanations, and test parallel ideas that help get to the most likely answer. In the process, other scientists have ways to challenge each other and test competing ideas. At a certain point, you have a solid reason to believe a given explanation is worthwhile. When something is as important as wild salmon, a strong weight of evidence justifies corrective action.

So what can we do? As a temporary solution, the salmon farms should be fallowed (removing the farmed fish for a period) while the juvenile fish pass by on their way out to sea. But the best solution would be to raise salmon in closed tanks that keep the farmed fish separate from the wild fish and their environments. Consumers should urge grocery stores and restaurants to sell only environmentally sound seafood products and should avoid buying products that are not.

Some people argue that it would cost too much to move to closed system aquaculture, or even to fallow farms during juvenile migration periods. But salmon can't be seen just as a food source for people, and the costs of running any agricultural operation can't be seen to just encompass the money required to build and run the farms. Wild salmon are a critical part of ocean, river, lake, and forest ecosystems. They provide food for everything from whales to eagles to bears, and even help fertilize the forests along the shores, rivers, and lakes where they live and spawn.

Yes, everything is interconnected. If the wild salmon dwindle and die, next come whales, bears, and our forests... And where will that leave us?

April 18, 2008
http://www.davidsuzuki.org/blogs/science-matters/2008/04/fishing-for-salmon-answers/

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