Stocking density in salmon sea cages is a primary welfare determinant. Evidence links high densities to chronic stress, injury, disease, and reduced welfare across multiple indicators.
Stocking density is arguably the single most impactful variable in salmon sea cage welfare. At high densities, salmon experience multiple compounding welfare harms: reduced dissolved oxygen from competition for limited resources, increased physical contact causing fin and skin damage, elevated aggression from resource competition, and higher pathogen loads from waste accumulation. Chronic crowding stress suppresses immune function, increasing disease susceptibility and requiring more antibiotic use. Economic incentives push operators toward the highest density the regulations allow — or higher in inadequately regulated systems. The welfare evidence clearly supports lower densities: salmon at 15-20 kg/m³ show better welfare, growth, and survival than those at 25 kg/m³ or above. Consumer demand for lower-density certified salmon can effectively drive density reduction.