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That dietary advice has changed the way the world consumes salmon, pushing consumer demand ever upward and production to higher and higher levels. Most of that demand is being met with farmed salmon: Today, nearly 70 percent of the salmon consumed on the planet are raised in pens and cages.
The US Department of Agriculture’s Dietary Guidelines for Americans recommend eating at least 8 ounces of fish a week and urges people to choose salmon or other species that are similarly high in “heart-healthy” Omega-3 fatty acids. But new research led by USDA scientists finds that levels of these fatty acids in farmed salmon have dropped considerably, potentially making the agency’s own advice, and similar recommendations, including from the American Heart Association, outdated and insufficient.
“These old figures are what are still used in their national dietary guidance,” said Laura Lee Cascada, director of the Aquaculture Accountability Project, a watchdog group. “So in the meantime, it’s going to stay the same and people will have this wrong idea of how much Omegas they’re getting.”
The report’s authors note in their research that the sample they examined was not large enough to require changing the government’s advice and that “a broader and more representative study is warranted.” The agency declined requests for an interview and did not answer questions via email.
The reason for the decline of the Omega-3s, the new study says, is a major shift in the diets of the naturally carnivorous salmon, from smaller fish species—which were over-exploited to feed farmed fish—to a mix that includes land-based oils and crops, including soy and canola. A 2016 study noted similar declines, also attributable to the shift toward a crop-intensive diet.
So, as the well-intended dietary advice has driven a surge in farmed salmon consumption, the corresponding surge in production appears to be depleting the very nutritional benefits that prompted the global salmon boom in the first place—and with consequences for both the marine and terrestrial environment.
Salmon has played a key role in the explosive growth of global aquaculture, becoming a mainstay in the diets of health-conscious eaters or those trying to cut down on terrestrially farmed protein, especially beef, for both health and environmental reasons. The amount of farmed salmon tripled between 2000 and 2020, far outpacing the production of any other type of finned fish.
Today aquaculture is the fastest-growing food production system in the world, much of it spurred by increasing appetites for species, including salmon, that have been identified and marketed as uniquely healthful.
But researchers and advocates have long criticized the environmental impacts of farmed salmon. Fish waste and feed pollute waters, threatening wild-caught salmon populations. Feeding ever-greater populations of pen-raised salmon has led to the degradation of both smaller fish species and the coastal fishing communities that depend on them and other wildlife, including seabirds.
With the world’s oceans becoming increasingly depleted of small fish, the industry has switched to feeding salmon a diet based more on terrestrially grown crops, including soy and soy oils.
That shift has come with a new set of problems.
Most of the world’s soy, roughly 50 percent, is grown in South America where rainforests and other climatically important ecosystems are being razed to grow feed for livestock and aquaculture.
“Soy is a major, important protein and oil ingredient in fish farming,” said Matthew Hayek, a researcher at New York University who studies the environmental impacts of protein production. “What we can tell is that, for all fish farming combined, soy consumption over the past two decades has amounted to the additional expansion and clearing of forested land that was equivalent to about the size of Nicaragua or Bangladesh.”
Hayek noted that it’s difficult to attribute soy consumption to individual fish species. But other research has found a rise in the use of crop-based ingredients fed to farmed salmon. In Norway, the world’s biggest producer of farmed salmon, 90 percent of feed ingredients were marine-based in 1990, but by 2020 that had dropped to about 23 percent. Advocacy groups there determined that 90 percent of the soy fed to farmed salmon in Norway comes from three Brazilian companies, each of which have sourced soy ingredients from illegally deforested patches of the Amazon rainforest.
Other research has found that the shift to crop-based ingredients doubled the greenhouse gas emissions, per kilogram, of farmed fish in Europe and the United Kingdom from 2000 to 2020.
“It’s trading one problem—marine exploitation—for another—land exploitation,” Cascada said.
The industry is projected to continue growing, along with the population and rising demand for seafood promoted as healthy. Nutritionists and researchers say that farmed fish, including salmon, will play a major role in providing protein, though some environmental groups note the surge in salmon demand has disproportionately come from wealthy countries that don’t have nutritional deficits.
“The claim is that the salmon industry is here to feed the world and provide this extra protein,” Cascada said. “But what it’s really doing is flooding the Global North with protein that is not necessarily needed at the expense of the Global South.”
In the United States, lawmakers are trying to help the industry expand by passing legislation that would make it easier for salmon producers to obtain licenses to farm fish in offshore federal waters.
In February, environmental advocates and fishermen sent a letter to members of Congress opposing the bill, the Marine Aquaculture Research for America (MARA) Act.
Proponents of the bill say that putting fish farms in deeper, offshore waters would reduce the environmental issues caused by farming fish in sensitive, nearshore environments.
Opponents say the legislation would enable a factory-farming model, much like the one that produces the vast majority of the world’s livestock, in the open sea.
