Examining the welfare conditions in conventional open sea salmon net pen aquaculture and what the evidence shows about key welfare challenges.
Net pen salmon welfare is structurally challenged by the open-water environment that creates excellent fish products but provides limited management control over key welfare determinants. Disease pressure from sea lice and gill pathogens is the primary welfare driver that determines flock-level suffering across the productive cycle. The welfare of individual fish within net pens is difficult to assess given the scale of flocks and the limitations of underwater observation, but disease prevalence data from slaughter monitoring and mid-cycle veterinary assessments provides population-level welfare indicators. The most impactful welfare improvements available are lice monitoring and management, disease prevention through vaccination and nutrition, and a transition to closed-containment systems that eliminate the environmental disease pressure that defines open net pen welfare challenges.