Yellowfin tuna (Thunnus albacares) is among the world's most commercially important marine species. Its welfare is relevant in both wild-capture fisheries (where billions of animals are caught annually) and in emerging tuna aquaculture. Understanding welfare implications helps consumers and industry make more informed decisions.
Biology Relevant to Welfare
Tuna are among the most physiologically sophisticated fish. They are obligate ram ventilators — they must swim continuously to force water over their gills. They maintain body temperatures significantly above ambient water temperature (regional endothermy) — a metabolically expensive adaptation enabling high-performance swimming. Their brain-to-body ratio is larger than many other fish, and they demonstrate complex schooling behaviour and spatial learning. These characteristics are welfare-relevant: tuna cannot be maintained in tanks without continuous water flow and cannot simply be placed in a holding tank without welfare consequences.
Wild-Capture Welfare Concerns
Yellowfin tuna are caught by purse seine nets (often in association with fish aggregating devices, FADs), longlines, and pole-and-line fishing. Each method raises specific welfare concerns:
- Purse seining: Mass capture of schools causes extreme stress; crowding during net closure; bycatch of other species including sharks and dolphins causes additional welfare and conservation harm
- Longlines: Fish may remain hooked for hours to days before retrieval; barotrauma, exhaustion, and dehydration cause significant suffering
- Pole-and-line: Individual fish are caught quickly; less stress and bycatch; considered the most welfare-positive commercial method
Post-Capture Handling and Slaughter
Spiking (ike jime) — a traditional Japanese method involving immediate brain destruction followed by spinal cord pithing — produces the most welfare-positive slaughter of tuna. It also improves meat quality substantially (preventing lactic acid accumulation). The method is gaining adoption in premium tuna fisheries globally. Alternative methods — live chilling in ice slurry, CO₂ anaesthesia — are less welfare-positive but widely used commercially.
Tuna Aquaculture
Commercial tuna farming (bluefin more commonly than yellowfin) typically involves capture of wild juvenile fish and grow-out in sea cages. Mortality during capture, transport, and adaptation to captivity is high. The failure to develop tuna from egg to harvest in captivity means aquaculture remains dependent on wild juveniles, raising both welfare and conservation concerns.