Crowding in salmon sea cages affects behavioural expression, social dynamics, and stress physiology, with significant implications for individual welfare across the production cycle.
Salmon crowding welfare operates through multiple pathways simultaneously. Social dominance hierarchies in crowded conditions mean that subordinate fish consistently receive less feed, grow more slowly, and experience chronic stress from repeated aggressive displacement. Fin erosion resulting from biting and physical competition is visible and measurable, providing a proxy welfare indicator that can drive management decisions. Behavioural space needs - the ability to school coherently, seek preferred depth, and avoid dominant individuals - are unmet in overcrowded cages. The welfare argument for lower stocking density is further supported by evidence that less crowded fish have better immune function and lower disease susceptibility, aligning welfare and productivity interests.