Yellowfin tuna or Ahi in Hawaii, are a prize pelagic gamefish that live in tropical and subtropical waters around the world. They are beautiful, tasty and can get quite large. With some adults weighing up to 400 pounds and almost 7 feet in length, they are also some of the fastest fish in the ocean. One standout feature is that mature yellowfin tuna have long sickle fins that develop which can reach almost as far back as the tail.
These fish are found in deep offshore waters and travel in schools with similar size fish. Although living in deep water, they rarely dive past the first 300 feet of water. Another key to locate these particular fish is to look for schools of dolphins and porpoises. Yellowfin are usually found just under these schools chasing after the same bait. Metering the fish is common practice so using a depth sounder is really useful. Often times, divers have to dive through dolphins to reach the school of yellowfin swimming underneath them. Top spots for these fish include South Africa, Mexico, and Ascension Island.
Yellowfin tuna do migrate seasonally. They came be found year round depending on where you are in the world in water temperatures that ranges from 64 to 80 with 72-73 is optimal.
As mentioned above, these fish move extremely fast. Two common techniques to hunt these fish are chumming, and free-swimming along the edge of drop offs. I use flashers regardless if I am chumming or not. Chumming makes things much easier when targeting yellowfin. However, chumming can attract sharks which can cause bigger problems than trying to shoot a fast moving fish. These fish move so fast so its important to time your shot with the fish approaching the chum. Be sure to dive and aim at the chum or bait right when the fish approaches it. Chumming works well for attracting small to medium size yellowfin, but the larger grade fish are usually encountered free-swimming. When free-swimming try to work your way to the up current side of the reef's drop off zone. When you see a fish, never swim directly at it. I try to swim at a point of intersection well in front front of the fish. This technique will allow you to get close enough and usually the fish will veer off giving you a good shot. Recommended gear for these fish include two different schools of thought. The first school of thought is popular in South Africa and other European countries. Longer two banded guns with smaller diameter shafts around 7.5mm are used because these guns are light and easier to dive with in the water such as Rob Allen spearguns. The narrower shafts are like needles penetrating easily into the fish at close range. The second school of thought would be big bluewater spearguns with thick shafts, 8mm-10mm, and at least four bands. These guns are heavy, but have maximum penetrating power out to far distances 25'-30'). Manufactures of these guns include Nitro gun Co, Ulusub, and Andre spearguns.