The yellowfin tuna inhabits warm waters throughout the world’s oceans, often favoring deep oceanic areas. Although capable of making deep dives, yellowfin spend the majority of their time in the top 300 feet, usually above the thermocline. The migratory species is known to make long migrations, which range from relatively close to shore to hundreds of miles offshore.
The yellowfin tuna’s diet is varied and depends on what’s available. They will feed on flying fish, squid, crustaceans and a range of small fish, including other tuna. The yellowfin is known to school primarily by size, either in monospecific or multi-species groups. Larger fish frequently school with porpoises, also associated with floating debris and other objects. Peak spawning occurs during the summer months. Yellowfin are estimated to live up to seven years or more.
Yellowfin tuna are the most colorful of all the tunas, with a dark black back, silver sides and a bright yellow strip running up its flank. The fins and finlets are golden yellow, and sometimes edged with silver. The fish’s belly frequently shows up to 20 vertical rows of white spots.
The yellowfin tuna can be distinguished from other tunas by the overextended second dorsal and anal fins found on large fish. However, these large fins don’t always show up in all specimens. Yellowfin can be distinguished from blackfin tuna by the black margins on its finlets. Blackfin tuna, like albacore, have white margins on the finlets. Yellowfin are often confused with big eye tuna. The only true way to tell the difference between a yellowfin and a big eye is to look at the animal’s liver. The big eye tuna has a lack of striations on the ventral surface of the liver. The big eye also has a larger eyeball, and smaller second dorsal and anal fins.
As one of the most valuable food fish in the ocean, commercial purse seiners and long liners seek yellowfin tuna for big paydays. Yellowfin tuna has become one of the most popular fish served today. You’ll see it on restaurant menus around the world served up grilled or raw as sashimi. It is also canned. Because yellowfin tuna populations are dispersed throughout the world, it’s nearly impossible to get an accurate population assessment. The species is often categorized as “near threatened.”