Yellowfin tuna ranching captures wild fish for fattening in sea cages, raising welfare concerns about capture stress, pen confinement for a highly active pelagic species, and slaughter methods.
Yellowfin tuna welfare in ranching systems is severely compromised from capture onward. Purse seine capture involves extreme crowding, exhaustion, and oxygen depletion. Transfer to sea cages causes further stress and capture myopathy in some fish. In cages, continuously swimming pelagic tuna are confined in a fraction of their natural range, with restricted depth and swimming distance. These conditions cause chronic stress, abnormal behaviour, and injury from cage collisions. Conventional slaughter without stunning causes prolonged, distressed death. The welfare profile of tuna ranching requires fundamental improvement before it can be considered an acceptable production system.