The Pew Environment Group report found that in 2010, the amount traded on the global market was 141 percent above allowable catch levels (32,564.9 metric tons). That doesn't include "black market" bluefin missing from trade records. Discounting illegal fishing, the Fisheries Service's denial of listing for the bluefin determined that a 5 percent probability of extinction in 20 years is a reasonable threshold for endangered status. At catch levels of 30,000 metric tons, there is an 8.5 percent probability that fewer than 500 adult bluefin tuna will survive in 2030.

Highly migratory, warm-blooded fish, Atlantic bluefin tuna include two genetically distinct populations, one that spawns in the Mediterranean (the "eastern Atlantic" stock) and a much smaller population that spawns in the Gulf of Mexico (the "western Atlantic" stock). Today's analysis of the eastern Atlantic stock has implications for both stocks because of cross-Atlantic mixing. Capable of speeds over 55 mph, bluefin tuna from the Mediterranean traverse the ocean in a matter of weeks as early as age one. Overfishing means that fewer Mediterranean tuna reach U.S. waters.