The bluefin tuna is one of the biggest, fastest fishes in the ocean. Its streamlined body can sprint at up to 45 miles per hour in pursuit of its prey. Reaching some 500 pounds, this giant once dominated the Atlantic, Pacific and Indian oceans. But humans have hunted the bluefin for thousands of years. In the last century stocks have been decimated. The Pacific population is now just 2.6 percent of its original size.