Paper: Fry, J.P., Love, D.C., MacDonald, G.K., West, P.C., Engstrom, P.M., Nachman, K.E., Lawrence R.S., (2016). Environmental health impacts of feeding crops to farmed fish. Environmental International. 91:201-214. doi:dx.doi.org/10.1016/j.envint.2016.02.022
Global seafood supply has changed dramatically in the past few decades. Historically, seafood supply has come mostly from wild-caught fisheries; however, there are only so many fish in the sea. As wild fisheries were fished to and beyond their capacity, aquaculture or fish farming became an opportunity to feed the growing world’s appetite for seafood without overfishing. Aquaculture production has increased steadily and now makes up about half of the global seafood supply. However, aquaculture production methods are changing which may result in unintended consequences. For example, around two-thirds of farmed seafood such as salmon and shrimp require nutrients from feed. Key ingredients in feed commonly include fishmeal and fish oil from wild-caught fish; however, as the aquaculture industry continues to expand and wild fisheries reach their limits, it is becoming more attractive to substitute other ingredients such as poultry byproducts, insects and land-based crops such as soybeans. What does this mean for resource use and human health? Fry et al., 2016 took a look at the potential outcomes of linking land-based ingredients to commercial aquaculture.
The first step was to estimate resources involved in producing terrestrial crops used in aquaculture feed: processed soybean, rapeseed/canola, maize, nuts and wheat. Then, two literature reviews were conducted to investigate how agricultural practices are impacting human health in terms of environmental health and nutrition.
The authors estimated that in 2008, ~99,000-104,000 km2 of land (comparable to the size of Iceland) was used to grow the main five agricultural crops for aquaculture feed. Furthermore, almost twice as much soybean meal (the most extensively used crop-based ingredient) compared to fishmeal oil was used as an ingredient in commercial aquaculture feed in 2008. By linking terrestrial crops to aquaculture, aquaculture’s environmental footprint now includes area of land use, fertilizer and pesticide use, as well as water used for irrigation.
In terms of human health, increasing agricultural production did not seem to improve the situation. Farming commercial crops involves the application of fertilizers and pesticides that often produce excess runoff as the crops do not uptake the entire applied amount. The literature review found that agricultural runoff has many undesirable consequences such as degradation of water quality for recreation, fishing or drinking leading to potential birth defects and numerous forms of cancer such as stomach cancer, colorectal cancer and more. Negative impacts were higher for those living in proximity or downwind from agricultural applications of fertilizers and pesticides. However, long-term agricultural workers in direct contact with fertilizers and pesticides were the most vulnerable. It is estimated around 10,000-20,000 agricultural workers in the U.S. experience some level of pesticide poisoning every year. Again, by linking land-based agriculture to aquaculture, aquaculture takes on negative human health externalities.
Finally, what do more land-based crops in feed mean for the nutritional content of farmed seafood? Well, it turns out that the general trend for substituting land-based ingredients into aquaculture feed reduces the amount of EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), better known as omega-3s—the reason seafood is regarded by the World Health Organization and the U.S. Food and Drug Administration as part of a healthy diet.
Taking all of these potential impacts into account, Fry et al., 2016 came up with the framework below (Fig 2) that summarizes the direct and indirect human health impacts of linking agriculture with aquaculture.
While there are many unknowns and data gaps, this framework highlights areas for future study. For example, studies on aquaculture feed should include measurement of omega-3s in the final seafood product. As well, nutritional content and the supply and demand of all ingredients in aquaculture feed should be closely monitored. By tracking how aquaculture production is changing, we can use this information to ensure aquaculture contributes to an energy and resource efficient, as well as healthy global food system.