Open net pen aquaculture for salmon and other species raises both welfare and environmental concerns that are increasingly linked in policy discussions about sustainable and humane seafood production.
Net pen aquaculture welfare and environmental impact are increasingly understood as inseparable. The open exchange between farm cages and the surrounding marine environment means that disease agents, parasites, and waste from high-density fish production affect both farmed and wild fish. Sea lice at high densities cause welfare suffering to farmed fish while also spreading to wild juvenile salmon and sea trout nearby. Escapes spread disease and genetic material to wild populations. Waste from high-density feeding enriches sea floor sediment with consequences for local ecosystems. Welfare improvements for net pen salmon — lower stocking densities, improved disease management, cleaner fish use, and reduced chemical treatments — often align with reduced environmental impact. The transition to land-based closed systems eliminates these environmental exchanges but requires substantially higher energy inputs and capital costs.