Yellowfin tuna, also known as ahi tuna from their Hawaiian name, are epipelagic- they exist in the upper 300 feet of the seas. These graceful fish can weigh over 400 pounds and swim steadily at over 20 miles per hour. Research has found that it may be the mineral Magnetite, present in neural pits in the tuna’s snout, which helps the tuna to navigate, through its detection of the earth’s magnetic field. Tuna are extremely fast and powerful due to their streamlined shape and ability to reduce drag by retracting their angled fins. In addition, unlike most fish, they are warm- blooded and can heat their bodies up 40 (F) degrees warmer than the surrounding water which in turn heats their muscles, increasing efficiency. Yellowfin tuna currently have a fairly stable population but are becoming a replacement in fisheries for the declining bluefin tuna. They are commonly caught with purse seines which also bring in many tons of bycatch per year. Less damaging techniques such as handline or pole fishing can also be used.