A new study in this week’s Science finds that the two distinct Atlantic bluefin tuna populations — those spawned in the Gulf of Mexico and those spawned in the Mediterranean Sea — meet during their juvenile years in the Atlantic before returning to their respective natal homes to reproduce.
In addition to being fascinating (the authors studied isotopes found in juvenile tuna ear bones used for balance, called otoliths, as they contain chemical markers delineating water composition), the study underscored a very important point about bluefin tuna conservation. While there are two distinct spawning grounds, the tuna intermingle — meaning that U.S. fisheries may actually be catching eastern, Mediterranean tuna, and vice versa.
Why does this matter? For two reasons: One, because Atlantic tuna as a whole are already teetering towards extinction. Two, because the International Commission for the Conservation of Atlantic Tunas, the body responsible for keeping tuna around, divides the Atlantic lengthwise and considers the two populations completely distinct. A tuna caught west of the 45th meridian, then, is considered a western bluefin even if it was born an eastern bluefin.
These fish cannot afford to be accidentally counted with the wrong population of bluefin tuna. The authors suggest that one result of these migratory juveniles is that there may actually be even fewer western Atlantic bluefin than we thought. Furthermore, the rampant overfishing going on in European waters may be disproportionately affecting migratory juveniles from the western population. Either way, the migrating fish haven’t had a chance to reproduce, wherever their home.
ICCAT has no great history of living up to its name; some joke that it should be called the International Conspiracy to Catch All Tuna. An independent assessment of ICCAT’s work, to be revealed at its Nov. 16 meeting in Morocco, calls it “a travesty in fisheries management.”
Hopefully this new science will lead to what conservationists on both sides of the Atlantic have been calling for: a complete moratorium on catching Atlantic bluefin.