Atlantic salmon in sea pen aquaculture face welfare challenges from high stocking densities that prevent expression of natural swimming and schooling behaviours.
High stocking densities in salmon sea pens prevent normal schooling behaviour, restrict individual movement and create conditions for aggression and disease. Fish in overcrowded pens show higher cortisol, fin erosion and compromised immune function. The welfare cost of high density production is well-documented. Maximum density regulations provide welfare floors but evidence suggests optimal welfare requires densities below regulatory maxima. Consumer and retailer demand for certified welfare standards with density requirements drives commercial adoption of lower-density production.