Yellowfin Tuna Facts

A yellowfin is built for aquatic efficiency, its fusiform (torpedo) body tapering from a thick, muscular midsection to a slender tail base; adults run 3 to 6 feet, with giants to 7 feet and 440 pounds. Coloring is classic pelagic countershading — dark metallic blue above to vanish into deep water, silver-white below to hide against the sunlit surface — and the signature feature is the exceptionally long, bright-yellow second dorsal and anal fins trailing like sickles, with a row of small yellow finlets down to the tail. Its warm-bloodedness comes from counter-current heat exchangers (retia mirabilia): networks of vessels that transfer heat from the swimming muscles to blood returning cold from the gills, keeping some tissues warmer than the sea and widening the range of temperatures it can hunt in. It belongs to the mackerel-and-tuna family Scombridae, and like its kin it is an obligate ram ventilator — it must keep swimming to force oxygen over its gills, or suffocate.

The yellowfin is a highly migratory, open-ocean fish found circumglobally in warm tropical and subtropical waters of the Atlantic, Pacific, and Indian Oceans, off the U.S., Mexico, Japan, Australia, the Philippines, the Seychelles, and Ecuador among many. It rarely comes near coastal shallows unless steep drop-offs give quick access to deep water, mostly occupying the sunlit epipelagic zone in the warm upper 330 feet — though it can dive well below 3,000 feet to hunt squid in the cold, dark mesopelagic, protected by its warm physiology.

Yellowfin tuna are active pursuit predators that eat schooling fish such as mackerel, sardines, and sauries, as well as pelagic crustaceans and squid. They may break the surface while pursuing flying fish. A yellowfin can exceed 40 mph in short bursts, and schools may concentrate small fish near the surface before feeding.

Yellowfin form schools that can contain thousands of fish, often sorted by size. They also aggregate with skipjack and bigeye tuna. In the eastern Pacific, mature yellowfin often swim below spotted and spinner dolphin pods, an association historically used by fishing fleets to locate tuna.

Yellowfin are broadcast spawners. In warm tropical waters, a large female can release several million eggs in one event, with fertilization occurring in the water. The eggs drift in the plankton and hatch within 48 hours. Most larvae are eaten, but survivors grow quickly and may reach 10 pounds in about 18 months. Yellowfin typically live 6 to 9 years.

The yellowfin tuna is Near Threatened with a steadily decreasing global trend. The overwhelming threat is industrial overfishing: prized worldwide for sushi, sashimi, and canned tuna, it is targeted by large fleets using purse seines and longlines. Purse-seine fishing on tuna that swim beneath dolphin pods historically caused massive dolphin bycatch, prompting "dolphin-safe" standards. Regional fisheries bodies set catch quotas, but illegal, unreported, and unregulated fishing continues to deplete yellowfin stocks across the world's oceans.

• IUCN Red List of Threatened Species: Yellowfin Tuna
• World Wildlife Fund (WWF): Tuna
• Monterey Bay Aquarium Seafood Watch: Yellowfin Tuna