May 11, 2012

The Big, Fat, Hungry Salmon Industry

Christine Grillo

Christine Grillo

Contributing Writer

Johns Hopkins Center for a Livable Future

Floor of a salmon cannery

Salmon steak. Salmon burgers. Salmon tartare. Is salmon the new beef? Some say yes. If that’s true, hurray for the planet, which desperately needs a break from resource-intensive beef production. (Check out this article, which quotes CLF’s Roni Neff, about the negative effects of beef production.)

But not so fast with the rejoicing. By taking the predatory, carnivorous fish that we enjoy eating, such as salmon, swordfish and tuna, from their natural habitats, we risk overfishing (and depleting) fisheries, and disturbing marine ecosystems. Aquaculture seemed like a viable solution to overfishing—we would simply farm the fish, and not mess with the ecosystems. But salmon farmers have to feed the salmon they’re raising, and salmon is a hungry master. CLF’s Dave Love, PhD, says that it takes between two and three wild fish to feed one farmed predator like salmon.

Earlier this year, scientists at the University of Oviedo (Spain) published results of a study in which they investigated what, exactly, is being fed to farmed predators like salmon. (Coverage of the study here.) And I do mean “exactly:” they used mitochondrial 16S rDNA to analyze commercial samples of three types of fish meal sold in Spain and fed to farmed species in Europe. What they found calls into question the current practices used in aquaculture.

It has been assumed that farmed fish are nourished on fish pretty far down on the food chain, such as menhaden, anchovies, and sardines. But the Spanish investigators found that their samples of fish meal contained DNA from eight large, predatory fish high on the food chain. (Fish, like all animals, are rated on a trophic scale, which indicates their place on the food chain; algae rate a score of one, sardines rate a two, tuna and salmon rate in the high threes or close to four, and orcas rate a five.) What this means, says Love, is that “Predators being raised in captivity are being fed other predators caught in the wild.” Aquaculture, he says, needs to reduce its ecological footprint.

The authors of the study suggest that of those eight predatory species, the presence of up to six species can be explained satisfactorily. Because these six species are sold after processing—canned, smoked, slated, dried, etc.—we can deduce that the aquaculture industry purchases the post-production scraps (bones, spines and heads) and uses those scraps to make fish meal. (The six species identified are: Peruvian anchovy, European sprat, Pacific cod, whiting, jack mackerel, and blue mackerel.)

But two of those eight species cannot be explained with the “scraps” theory. The Atlantic herring and the Pacific sandlance are sold exclusively as whole fish. So how has DNA from these two fish (with trophic levels of 3.79 and 3.1, respectively) ended up in fish meal, which is fed to farmed salmon? That is an interesting question indeed. Love offers a couple of possible explanations: perhaps the big fish are caught unintentionally in nets and used for meal, or maybe they go bad, get tossed, and then are used in fish meal.

The authors of the study write that the findings suggest that “aquaculture, in a wide sense, in being maintained at least partially by fisheries, and that farmed fish are fed by wild fish.” They further state, “These results suggest the urgency of revising fish meal composition and progressively replacing fish-derived protein by proteins from other sources in aquaculture, in order to decrease the exploitation of wild fishes.”

Love suggests that a small, incremental step would be to introduce vegetable proteins (like soy or algae) as an alternative to animal protein. The sea-change decision, he says (and I think the pun was intended), would be to stop farming predators and instead farm herbivorous fish. He further notes that chicken was found in the fish meal, and that fish scraps are used in food for dogs, cats, pet fish, and in fertilizer. Whether wild predatory fish are intentionally caught and fed to predators in captivity, or not, Love says, “It’s a broken system, and it’s lunacy.”

More information about the study:
A. Ardura, J.L. Horreo, E. Hernandez, A. Jardon, I.G. Pola, J.L. Martinez, E. Garcia-Vazquez. Forensic DNA analysis reveals use of high trophic level marine fish in commercial aquaculture fish meals. Fisheries Research, 2012

Photo credit: Oregon State University Special Collections and Archives

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