Managing salmon biomass in net pens involves periods of intentional crowding during treatments, harvest, and grading. These crowding events are among the most acute welfare stressors in salmon aquaculture.
Salmon crowding welfare is a microcosm of the broader challenge in aquaculture — necessary management procedures cause predictable welfare harm that can be minimised but not eliminated. The welfare imperative is to reduce crowding duration, maintain water quality throughout, and limit the frequency of crowding events through planning and efficiency. Farms that crowd fish multiple times for sea lice treatments, grading, and harvest create cumulative stress loads that affect immune function and disease resistance throughout the production cycle. Welfare-positive biomass management integrates treatment scheduling, harvest timing, and fish handling protocols to minimise total crowding exposure. Technology including real-time oxygen monitoring, automated aeration systems, and wellboat transfer systems reduces the welfare impact of unavoidable crowding events.