Bluefin tuna ranching — capturing juvenile wild tuna and fattening them in sea cages — combines wild-capture welfare concerns with aquaculture confinement stress in ways that raise significant welfare questions.
Bluefin tuna ranching welfare combines the worst aspects of wild-capture and aquaculture: the capture stress and mortality of fishing, followed by the confinement stress of aquaculture for animals evolved for enormous oceanic ranges. Wild tuna capture for ranching causes acute welfare harm in the capture process — the nets, crowding, transfer to tow cages, and transport — that is measurable in mortality and stress physiology. Subsequent ranching confinement imposes chronic welfare costs on animals whose behavioral ecology requires the kind of movement space that no pen can provide. Consumer choice for alternatives to bluefin tuna products sends market signals that affect the economics driving bluefin ranching expansion.