This June 21, 2010 NY Times article states that "Atlantic bluefin tuna..(is) a fish that regularly journeys between America and Europe and whose two populations, or “stocks,” have both been catastrophically overexploited. The BP oil spill in the Gulf of Mexico, one of only two known Atlantic bluefin spawning grounds, has only intensified the crisis. By some estimates, there may be only 9,000 of the most ecologically vital megabreeders left in the fish’s North American stock, enough for the entire population of New York to have a final bite (or two) of high-grade otoro sushi. The Mediterranean stock of bluefin, historically a larger population than the North American one, has declined drastically as well."
You can read the full article here.