Only adult bluefin (over 620 lbs and 12 years old) are found in the Gulf of Mexico.  They are there to participate in spawning for about 5 weeks beginning about May 1 each year, after which they migrate to rich feeding grounds in the northern end of their range - Nova Scotia and the Gulf of Maine.  Due to overfishing of their primary prey (herring, whiting, menhaden, etc.),  more and more bluefin are following the Gulf Stream toward the Azores and beyond intermixing with Mediterranean-spawned bluefin.