The science of sustainable seafood, explained

Replacing fish-based aquaculture feed with plant-based increases environmental impacts

The sustainability of farmed seafood is directly tied to how efficiently the animals turn their feed into flesh, aka food for people. Farms that use more feed to grow the same amount of food are more impactful than others. But what also matters is the kind of feed given to cultured species. Typically, fish and shrimp are fed fishmeal, a kind of feed made from ground-up fish. Fishmeal can be made from the excess trimmings of fish processing, but there are several wild-caught fisheries that only serve to be reduced into fishmeal for aquaculture, e.g. Peruvian anchoveta. However, with a growing market for farmed seafood, fishmeal is in high demand.

This has raised fishmeal prices worldwide; so some shrimp farms, most of which are in developing countries, have begun to substitute fishmeal with plant-based feeds. A recent paper in Sustainability, Malcorps et al. 2019, set out to measure the environmental and social impact of substituting fishmeal for plant-based feed in farmed shrimp. Currently, shrimp feeds are 20-30% fishmeal, depending on the shrimp species being farmed—what would the environmental impact be if those percentages dropped?

Malcorps et al. 2019 built a computer model to assess the changes in land, freshwater, and fertilizer use caused by substituting a portion of fishmeal shrimp feed with plant-based feed. The model found that substituting fishmeal with plant-based feed led to a dramatic increase in terrestrial resource demand for the 5 crops commonly used for substitution (wheat, soybeans, rapeseed, pea, and corn). A maximum plant-based substitution in shrimp feed would lead to a 63% increase in freshwater use, 81% increase in land use, and an 83% increase in phosphorus (fertilizer) relative to the current levels in those 5 crops.

Further, and more concerning, is the notion that increased demand on those 5 crops would raise prices and seriously impact poor families that rely on them for food.

Plant-based food vs seafood

Malcorps et al. 2019 covers a common theme of our website—the environmental impact of food (and seafood) on a global level. The conclusion from this paper are similar to the ones I discussed in a blog on the rise of the plant-based seafood trend. Essentially, replacing seafood (in this case fishmeal, which is basically seafood for other seafood) with plant-based alternatives is generally not beneficial to the planet. When managed well, fisheries are renewable, while terrestrial land is not. The cost of increasing crop sizes is loss of forests, wetlands, and innumerable biodiversity.

Reducing agricultural impacts and stopping climate change are the most important ways to slow the loss of biodiversity. On an individual level, the best thing you can do is watch your diet, but large-scale biodiversity protection will come from policy and institutional change that you affect with your vote. Register to vote in the U.S., here.

Picture of Max Mossler

Max Mossler

Max is the managing editor at Sustainable Fisheries UW.

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