Until the 1970’s, bluefin tuna fishing was merely seen as a recreational past time, with a giant bluefin having a commercial value of just $0.05 per lb. Trophy tuna were often sold to dog and cat food manufacturers. This all changed in the 1970’s when the Japanese speciality food market for sushi and sashimi opened making bluefin tuna suddenly represent large amounts of money for sport fishermen. This economic opportunity changed the perspective of fishing of bluefin tuna and by the late 1970’s, a giant trophy fish was a highly valued Japanese delicacy. The market growth boomed and giant bluefin fishery capitalised very quickly.
In the modern day, only a small scale catch-and-release sport fishery exists in the Bahamas, and virtually all other fish caught are marketed commercially. There is only one fishery in the United States that is allowed to catch bluefin tuna smaller than the minimum commercial size (1.78 m from the tip of the fish’s snout to the fork of its tail) present from North Carolina to Massachusetts.
http://marinebio.org/species.asp?id=236 Marine Bio Conservation