The pre-harvest phase for farmed salmon involves crowding for pump transfer and holding before slaughter. This period causes intense acute stress and welfare assessment is complex given the scale of operations.
Pre-harvest welfare represents the last welfare opportunity in the farmed salmon lifecycle - and also one of the most difficult to manage given the scale. Crowding tens or hundreds of thousands of fish for transfer involves unavoidable stress that can only be minimised, not eliminated. The welfare calculus involves duration (shorter transfer is better), density peaks (lower is better), water quality (oxygen and temperature maintained), and the fish's physiological state at transfer. On-site killing facilities at the farm would eliminate well-boat transport stress entirely - this is emerging technology that welfare-positive salmon farming is beginning to adopt.