High stocking densities in salmon sea cages cause chronic stress that suppresses immunity, increases aggression, and reduces welfare throughout the production cycle.
Salmon at high stocking densities cannot avoid aggressive conspecifics, maintain their preferred position in the water column, or access feed without competition. Chronic crowding stress elevates cortisol, suppresses immunity, and impairs healing. Fin damage from aggressive interactions is widespread. The economic incentive to maximise stocking density runs contrary to welfare. Lower densities reduce disease pressure and medication costs, providing a business case alongside welfare improvement.