Mid-Atlantic waters are proving to be hotspots for fish from both sides, and international fleets have been longlining here for the past decade, further disabling the recovery of West Atlantic fish.
More important, tagging has revealed that although some tuna from each fishery engaged in trans-Atlantic tourism, fish from the Mediterranean spawning ground are flocking to the western Atlantic like European tourists enjoying a favorable exchange rate on the dollar.
Data from electronic tagging by Block's team demonstrate that juvenile bluefin come from the Mediterranean to feed along the North American coast for one to three years, then return to the Mediterranean to spawn. They do so in larger numbers than those tuna spawned in the Gulf of Mexico that traveled east. This imbalance turns out to be critical to assessing how many fish in the Gulf of Mexico stock are left.
It appears that the continued presence of Mediterranean fish, year after year, was adding a hidden subsidy to the native western Atlantic population, potentially making it appear healthier than it really was. In essence, the International Commission for the Conservation of Atlantic Tunas has been assuming that the western Atlantic fishery consisted entirely of tuna spawned in the Gulf of Mexico, and has set quotas beyond what the native population can sustain.
Tagging data also showed that bluefin primarily went to the Gulf of Mexico to spawn later in life than had been assumed: at age 12, not age 8. The two populations of Atlantic bluefin have slightly different life histories; Gulf of Mexico-spawned fish reach maturity later and grow more slowly than the Mediterranean population.
"For the past two decades, we've been lowering the age for a comme
|Contact: Louis Bergeron|