The growing global appetite for seafood has driven an increase in aquaculture production. While often promoted as a sustainable alternative to wild-caught fish, the environmental impact of aquaculture, particularly its reliance on feed, has come under scrutiny.
A common argument in favor of aquaculture’s sustainability is its low consumption of wild fish. However, this assessment often overlooks the indirect use of wild fish in the form of trimmings and by-products incorporated into aquaculture feeds.
A study published in Science Advances by researchers from the University of Miami, Oceana, and New York University suggests that aquaculture may rely on significantly higher quantities of wild-caught marine fish than previously estimated. The study is part of a special issue focused on expanding the aquaculture industry’s contributions to food systems in order to achieve sustainability.
A New Calculation of Wild Fish Inputs
While the fish-in:fish-out (FI:FO) metric has been used to quantify aquaculture’s dependence on wild-caught fish, it has limitations and requires refinement. Previous calculations have often overlooked important factors such as recovered oil, trimmings, and bycatch. Additionally, the environmental impacts of land-based feed inputs, which are also used in aquaculture, have not been fully considered.
The research offers a reevaluation of the global fed aquaculture industry’s “fish-in:fish-out” (FI:FO) ratio, a key metric used to assess the efficiency and sustainability of aquaculture.
To address the issue, the researchers conducted a comprehensive analysis of feed composition data reported by the industry. By accounting for these hidden sources of wild fish, they found that the ratio of wild fish inputs to farmed products was significantly higher than previously estimated.
Key Findings of the Study
The results indicate that the proportion of wild fish inputs to farmed outputs is between 27% and 307% higher than previous estimates, with a range between 0.36 and 1.15, compared to a prior estimate of just 0.28. When considering the mortality of wild fish during capture and excluding unfed aquaculture systems, the ratio increases further to between 0.57 and 1.78.
For carnivorous farmed species in particular, such as salmon, trout, and eel, wild fish inputs likely exceeded twice the biomass of the farmed fish produced.
“Our study reveals that the aquaculture industry relies more heavily on wild fish extraction than previous research suggested,” said Spencer Roberts, a Ph.D. student at the Rosenstiel School in the Department of Environmental Science and Policy at the University of Miami and lead author of the study. “This demonstrates the scale at which aquaculture could be affecting marine ecosystems.”
The research team’s approach included considering previously overlooked sources of wild fish in aquaculture feed, such as trimmings and by-products from wild-caught fish. They also incorporated collateral fishing mortality, including “slippage,” a practice where unwanted catch is released but a large portion of the animals often do not survive. By analyzing multiple industry-reported datasets, the team provided a range of estimates and highlighted the uncertainties in current reporting practices.
The Trade-Off Between Wild Fish and Land-Based Ingredients
The researchers also examined the use of land-based ingredients in aquaculture feeds. While there has been a decrease in the use of wild fish in aquaculture feeds, this has come at a cost. The study found that widely cited estimates of reductions in wild fish use from 1997 to 2017 were accompanied by more than a fivefold increase in agricultural crops for feed production during the same period.
This trade-off raises concerns about the sustainability of aquaculture, as the production of feed crops can contribute to deforestation, water pollution, and greenhouse gas emissions. Furthermore, the increasing reliance on land-based ingredients may create competition for resources with food production for human consumption.
Implications for Aquaculture Sustainability
The findings of this study challenge the prevailing narrative of aquaculture as a sustainable solution for global food security. While aquaculture can play a role in meeting the world’s growing demand for seafood, it is essential to recognize its environmental costs, particularly in terms of wild fish inputs and the use of land-based resources.
“This research shows that the assumptions we’ve made about carnivorous aquaculture have been too optimistic, and it’s another reason to think strategically about the types of aquatic species that make the most sense to mass-produce,” said Jennifer Jacquet, co-author of the study and professor at the Department of Environmental Science and Policy at the Rosenstiel School.
The findings have significant implications for policymakers, investors, and consumers. The study calls for more comprehensive and transparent reporting on feed ingredients in the aquaculture industry and suggests that policies promoting aquaculture expansion for sustainability reasons should be reconsidered.
Conclusion
The researchers emphasize that while their study provides a more complete view of aquaculture’s environmental impacts, more research is needed to fully understand the sector’s effects on issues such as nutrient pollution, habitat destruction, and the spread of diseases to wild fish populations.
In this regard, to ensure the long-term sustainability of aquaculture, it is crucial to develop innovative strategies that reduce its reliance on wild fish and minimize its environmental footprint. This may involve investing in research and development to improve feed efficiency, exploring alternative protein sources, and adopting more sustainable aquaculture practices.
The study was funded by Spencer Roberts and Matthew Hayek from the Grace Communications Foundation.
Reference (open access)
Roberts, S., Jacquet, J., Majluf, P., & Hayek, M. N. (2024). Feeding global aquaculture. Science Advances. https://doi.org/adn9698
