Half of the fish eaten globally is now farm-raised, but the surge in fish farming has put a significant strain on marine resources, a new international study has found.
Fishmeal and fish oil, made from wild forage fish such as anchovies, have long fed farmed Atlantic salmon and other carnivorous fish. But consumer demand for long-chain omega-3 fatty acids has caused the aquaculture industry to balloon, squeezing the fish-food supply so far that alternatives must be relied upon to avoid a forage fish wipeout, says lead study author Rosamond Naylor, professor of environmental earth systems science and director of the program on food security and the environment at Stanford University.
"Most wild fisheries are either exploited or overexploited," she says. "As long as we are a health-conscious population trying to get our most healthy oils from fish, we are going to be demanding more of aquaculture and putting a lot of pressure on marine fisheries to meet that need," she says.
She noted that it takes about five kilograms of wild fish to create one kilogram of farmed salmon.
The global aquaculture industry is already using 68 per cent of global fishmeal and 88 per cent of fish oil, Prof. Naylor and her colleagues note in their paper, published online Monday in the Proceedings of the National Academy of Sciences.
Because of the squeeze on resources in recent years, fishmeal and fish oil prices have skyrocketed, forcing many companies to pursue alternatives in response. And as that transition continues to happen, consumers could see increased salmon prices, she says.
"It's easy to find some of these substitutes, but what's going to be then still very healthy for consumers might change," she says.
"You can take all of the fish oil out of salmon diets right now or you could substantially reduce it, but you would lose that benefit of the long-chain omega-3s."
She suggests consumers reduce farmed fish intake to a few times a week or purchase omega-3 caplets.
Aquaculture fish production has nearly tripled in volume from 1995 to 2007 because of rising consumer demand for omega-3 fatty acids found in oily fish such as salmon and heralded for reducing the risk of cardiovascular disease. The chase for omega-3-rich fish has seen an explosion of salmon farms and, with it, numerous infestations of sea lice, a marine parasite blamed by some researchers for devastating wild salmon populations in British Columbia.
But like humans, salmon need their own omega-3 supply, which they can only get from other fish, says Tony Farrell, a professor of biology at the University of British Columbia and research chair of sustainable aquaculture at the DFO-UBC Centre for Aquaculture and Environmental Research.
"That's why you can't replace in a salmon diet all of the wild fish," he says. "You have to have a little bit."
Prof. Farrell, who worked on the study with Prof. Naylor, says that in order to be sustainable, farms should fix fish-feed diets to be 80 per cent alternative nutrients and 20 per cent fishmeal and fish oil. That way, the salmon still get the oils they need, but the forage fish supplies won't be depleted.
Many aquaculture producers are pursuing vegetable long-chain oils such as canola to help them cut back on forage fish. Australian researchers are looking to genetically modify the omega-3 chains in these vegetable oils. Single cell oils and algae oils are being considered too, but they remain expensive. Norwegian researchers are investigating krill, a "subfish," as an alternative to fish meal, Prof. Naylor says.
Canada is leading the switch to more sustainable food sources, says Cyr Couturier, a research scientist at the Marine Institute of Memorial University in St. John's. Canada's aquaculture industry uses 25 per cent forage fish and oil to feed salmon, he says, while 75 per cent of the feed is from all-natural products, such as wheat.Moving the cold-blooded creatures onto more sustainable diets has been a gradual process.
Marine Harvest Canada now uses vegetable and poultry proteins in place of meal made from forage fish, says Clare Backman, director of environmental compliance and community relations from company headquarters in Campbell River, B.C.
Five years ago, Marine Harvest used 50 per cent fish meal and fish oil, respectively. Now they're using 15 per cent of each. "Our reliance on fish meal and fish oil right now has gone down," he says. "We're very aware that fish meal is getting to be a very rare commodity and we've been looking at ways of reducing our reliance on that."
In March, Fisheries and Oceans Canada introduced a policy on new fisheries for forage species such as herring, shrimp and capelin, aiming to ensure a sustainable supply.