The role of fisheries and fish farming in a circular food system in the European Union

Studies that demonstrated animals can contribute to resource efficient food supply, by upcycling low-opportunity-cost feed (LCF), into valuable animal-source food, focussed solely on livestock (ruminants, pigs and poultry). Aquatic animals, however, also make valuable contributions to food supply, especially as they are our main natural source of eicosapentaenoic (EPA) and docosahexaenoic (DHA) ω-3 fatty acids. Our aim, therefore, was to assess the contribution of capture fisheries and fish farming (salmon and tilapia) to human nutrient supply in EU-28 (before Brexit), when feeding no biomass from arable land or waterbodies but only LCF to livestock and farmed fish. To this aim, we deployed an optimisation model allocating available LCF in the EU under various scenarios, to that combination of fish and livestock that maximises human digestible protein supply, while meeting human requirements of vitamin B12 and EPA + DHA. We found that capture fisheries could fulfil maximally around 40 % of daily per capita EPA + DHA requirements in EU28. This contribution would already require rebuilding fish stocks and prioritising edible fish for human consumption. To meet our EPA + DHA requirements we, thus, need to additionally farm fatty fish (salmon). Our results show that, when feeding only LCF, these fatty fish depend on by-products from fisheries to meet their own EPA + DHA requirements and on livestock slaughter by-products to meet their high protein requirements. Feeding livestock by-products to farmed fish, however, is not common practice due to concerns about consumer acceptance. We also demonstrate that upcycling LCF into valuable human food requires a proper balance of different farmed fish and livestock systems, tailored to the available LCF and desired nutrient supply to the human population. Overall, our results provide insights into the role of aquatic animals across land and water to human nutrient supply and give a direction for strategic sustainability development of both capture fisheries and fish farming.