Tuna are considered epipelagic-to-midwater fish, inhabiting the upper and middle layers of ocean water, to a depth of 1,600 feet or more (500 m), depending on size and species. They are found in oceans the world over, except in polar seas. They roam long distances, following extensive north-south and even transoceanic migration patterns. Scientists and international organizations have tracked these patterns by the use of tagging. Fish tagged in the Bahamas have been recovered in Norway and even Uruguay. Others tagged in the Northeast have appeared off the coast of Europe. Tagged bluefin tuna have been known to travel over 4,800 miles (7,700 km) across the Atlantic in just 119 days—an average, assuming the fish swam in a straight line, of over 40 miles (65 km) per day. While yellowfin tuna seem to make less extensive journeys–most have been recaptured within 1,000 miles (1,600 km) of tagging–they have been known to travel over 3,100 miles (5,000 km).
For more wild facts about tuna, go to seagrant.gso.uri.edu