The researchers found that while the largest tuna - sought by commercial fishermen off North America - tend to be local fish, the smaller ones caught by sport fishermen often have originated in the Mediterranean.
The team, led by Jay Rooker of Texas A&M University and David Secor of the University of Maryland Center for Environmental Science, was able to identify the origins of fish by examining the chemical composition of the otolith, or ear stone, of the tuna.
"Juveniles are not conforming to the principal premise of how they've been managed - that fish keep to their own side of the Atlantic," Secor said in a statement. "This could be particularly troubling if North American juveniles head to the Mediterranean. High exploitation there might mean that few make it back.
Evaluating where Mediterranean juveniles originate should be our next highest priority."
The International Commission for the Conservation of Atlantic Tunas meets next month in Morocco to discuss declining tuna stocks and ways to better manage species.
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