What is the role of fish in a sustainable food future? Compared to other food groups, we have limited knowledge about the environmental impact of blue foods when it comes to greenhouse gas emissions and ecosystem impact.
So a team of researchers set out to fill the gap.
They gathered data from almost 7,000 fish farms and 1,000 fishery records about 23 species groups of fish, bivalves, seaweeds, and crustaceans. From this they built life cycle analyses that considered modes of production, land, water, nitrogen and phosphorus use, and emissions impact. The species they looked at collectively accounted for 70% of global blue food production, giving them a useful overall picture of the fishing and aquaculture industry’s environmental impact.
A few key patterns emerged. First, the major source of emissions in aquaculture is the production of feed for the farmed fish. In fact this accounted for a striking 70% of emissions for most farmed fish, most notably flatfish and crustaceans, the researchers found. The footprint is attributable to the land conversion and fertilizers that are needed to produce the feed, which are typically soybeans. This land-based food production also gives farmed fish a relatively high footprint where water use is concerned.
In wild-caught fisheries meanwhile, the primary emissions culprit is fuel-use for boats, especially true for high-seas industrial fleets that may travel long distances to capture fish.
This assessment also revealed which are the ‘greenest’ blue foods to consume. The researchers found that across all fish – farmed and wild-caught—the lowest-impact were farmed bivalves and seaweeds, mainly because they don’t need to be fed. In fact, their self-sufficiency gives them an ecosystem benefit, because shellfish and seaweed can remove nitrogen and phosphorus pollution—usually originating from terrestrial agriculture—from the water. What’s more, bivalves especially have some of the highest nutritional value of all available blue foods, presenting a clear win on all fronts.
The analysis also turned up a few surprising results, such as the fact that farmed shrimp were found to be less impactful than wild-caught. Also, consumers looking to make a difference by eating wild-caught salmon rather than farmed may be squandering their efforts: like trout, this fish had the same footprint whether farmed, or wild-caught.
By highlighting the several weak points in blue food production, the researchers also make it clearer where the opportunities are to make this increasingly influential source of dietary protein more sustainable.
As is often the case with food, the biggest opportunity lies in dietary change—in this instance, increasing our appetite for lower-impact bivalves and seaweeds. But while appetites adapt, there are also many changes to be made to the way we farm and catch fish, too.
The clearest opportunity there lies in feed. Crucially, finding ways to increase the feed conversion ratio (using less feed, more efficiently, to produce more fish) would bring substantial benefits. The researchers estimate that reducing the amount of feed applied in aquaculture by 10% could reduce all the associated environmental stressors of feeding fish—land use, water use, emissions—by between 1 and 24%.
If fish farms also switched to feed sourced from deforestation-free farms, emissions associated with feeding fish would drop by up to 50%. Beyond that, alternative feed sources like insect meals and algae, also hold a lot of potential to bring impacts down.
For open-ocean fisheries, where fuel use is the major concern, switching to more efficient gears (like trawl nets) that results in less fuel use, could lead to emissions reductions of up to 61%—and potentially limit ecosystem damage as well. Getting vessels to use low-emission fuels is another route, though that solution is still on a relatively distant horizon, the researchers say.
Ultimately, these changes will require time, policy interventions, and ideally subsidies to support more sustainable forms of blue food production. But unlike terrestrial agriculture, whose damage is so far-gone that we need to unpick it, with blue foods the good news is that we have the chance to intervene now and curb the damage before it reaches its peak—especially in aquaculture, because it’s still a developing industry.
“The global community now faces a unique window of opportunity to steer expansion towards sustainability,” the researchers say.
Source: Gephart et. al. “Environmental performance of blue foods.” Nature. 2021.