Pass by the fish counter of your local high-end supermarket, and you might see fillets of organic salmon on display. It’s still a bit of a fuzzy concept, but the label may give off planet-friendly vibes. But exactly how much greener is “organic” salmon? 
That’s a job for what’s called life cycle analysis, a technique often used to figure out how much energy and pollution it takes to make a particular product. Now it’s being applied to fish.
Nathan Pelletier of Dalhousie University, in Halifax, Canada, took a hard look at organic and conventionally farmed salmon in a session called “Sustainable Seafood: Cradle-to-Grave Assessments of Alternative Technologies.” ...
The big point for all farmed salmon, Pelletier and others noted, is that the greatest environmental impact is the fish meal that’s fed to salmon. “If we want to make great strides, we need to focus on replacing animal feed with crops.”
Based on a literature review, Pelletier compared the environmental impact of four sample diets that are, or could be, fed to farmed salmon in British Columbia. Then he analyzed their impact in about a dozen area, such as contributions to global warming or eutrophication of local waters.
In British Columbia, farmed salmon are usually fed a blend of fish meal from Peru, fish oil from the U.S., and poultry byproduct, along with soy and corn meal. Organic salmon must be fed the organic equivalent of the crops, and the fish products must come from a fishery that has been certified as sustainable or the byproduct of fish caught for human consumption. Pelletier also considered the possible impact of a fish diet that replaced organic crops with conventional crops, and an organic fish diet that used 25% less fish meal than before and replaced fish oil with canola oil.
Pelletier discovered the typical organic farmed salmon contributes most greenhouse gases; 2.7 tons of carbon dioxide equivalents for every ton of salmon, compared to 2.1 tons from conventional salmon. Reducing fish meal by 25% would cut the carbon dioxide emissions by more than half. This diet was also the most energy efficient, with these fish containing 18% of the industrial energy it took to grow them. Conventional salmon had about 11%, and the typical organic salmon had just 8%.
The major factor is the source of the fish meal. It’s efficient to harvest anchovies in Peru, for example, because they school in dense populations. More diesel fuel is needed to catch the fish whose parts are eventually fed to organic salmon: those caught for human consumption in sustainable fisheries.
In a related talk, Peter Tyedmers of Dalhousie also looked at wild salmon: He found that trolling (dragging fishing lines) is the most fuel-intensive way to catch wild salmon, emitting 1.6 metric tons of carbon dioxide equivalents per ton of salmon. Fishing by purse seine (a large net that is drawn closed) emitted less than 0.2 tons of carbon dioxide equivalents. “It’s hard to improve on purse seining,” Tyedmers said.
And this, of course, raises a dilemma for the eco-conscious consumer. As Kate Newman of the World Wildlife Fund pointed out during the Q&A, trolling is good for reducing the accidental capture of dolphins and other species, but it releases the most greenhouse gases. For Tyedmers, the choice is clear: “I’d sacrifice a few dozen species if we could stop climate change now.”
But George Leonard of the Monterey Bay Aquarium, science manager for Seafood Watch program, wasn’t so sure. What’s really needed, he said, is a “theory of everything” for life cycle analysis that could account for all the possible impacts. “What keeps me up at night is the thought that 30 years from now, we may realized we missed the boat.”
