Stocking density in farmed salmon net pens is a primary driver of welfare outcomes. Understanding the science behind density limits helps evaluate certification standards and consumer claims.
Stocking density is one of the most tractable welfare parameters in salmon aquaculture because it is directly measurable, regulatable and verifiable. At high densities, salmon cannot swim freely, subordinate fish are excluded from feeding areas by dominant conspecifics, fin damage from collision and aggression increases and wound healing is impaired. The economic incentive to maximise production per unit volume creates constant pressure toward higher densities. Welfare certification schemes that set and verify density limits provide a mechanism for market-based welfare improvement. The gap between Norwegian regulatory limits and RSPCA Assured limits illustrates that regulatory minimums may not represent best welfare practice. Consumers choosing certified lower-density salmon products create financial incentive for welfare improvement.