Reduced dependence on wild-caught fish in favour of crop-derived ingredients for feeds has been a central tenet of sustainable aquaculture growth. Yet there remains a superficial understanding of the environmental implications of changing raw materials in aquaculture feeds. Here we model the implications of shifts toward plant-dominant feeds for the environmental footprint (a cumulative and spatial measure of greenhouse gas emissions, habitat disturbance, water consumption, and nutrient pollution) of raw materials harvested to feed global salmon aquaculture. We show that, relative to fish-dominant feeds, plant-dominant feeds tend to reduce the habitat disturbance and greenhouse gas emissions from raw material production, but increase the nutrient pollution. However, where the raw materials that support aquaculture feed are produced drives considerably more variability in a feed's environmental footprint within feed types than across them. Policy and discourse on aquaculture feed sustainability 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.