Sourcing practices matter more than ingredients for the environmental footprint of salmon aquaculture feeds

Reduced dependence on wild-caught fish for aquaculture feeds has been a central tenet of sustainable aquaculture growth, particularly for carnivorous species such as salmon. Salmon aquaculture feeds are now largely dominated by crop-based ingredients in response to growing sustainability concerns surrounding the use of fishmeal and oil. Yet quantitative analyses of the environmental footprint of marine- or plant-dominant feeds and the variability of this footprint are lacking. Using global production, diet, and feed efficiency data, we present geospatial analyses of the cumulative environmental footprint (including greenhouse gas emissions, habitat disturbance, water extraction and nutrient pollution) generated from feeding the global farmed salmon industry either marine-dominant or plant-dominant feeds. We show that, relative to marine-dominant feeds, plant-dominant feeds reduce natural habitat disturbance, but their total environmental footprint tends to be similar due to trade-offs from water extraction and nutrient pollution (Figure 1). Importantly, where ingredients are sourced drives considerable variation in the cumulative environmental footprint within feeds such that the upper 97.6% of cumulative pressures scores for marine-dominant feeds overlap with the lower 97% of plant-dominant feeds. Policy and discourse surrounding the environmental sustainability of aquaculture feeds needs to better acknowledge the role that responsible sourcing can play for the sustainability of feed ingredients and the farming operations that rely on them.