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Tagging Reveals Details of Tuna's Transatlantic Travels

Large, powerful and prized for its meat, the Atlantic bluefin tuna has long intrigued human observers. Yet despite this, little was known about the fish's migratory movements. Now new research, described in this week's issue of the journal Science, is revealing the true scope of the tuna's wanderlust. Tagging data reveal that, among other things, many of these creatures regularly traverse the Atlantic and mix with the population on the other side, thus raising questions about current fish management policies.

To track the traveling tuna, Stanford University researcher Barbara A. Block and her colleagues fitted 377 bluefin tuna off the eastern coast of North America with electronic tags that recorded location, depth and water temperature every two minutes. The data┬┐collected starting in 1996┬┐make clear that transatlantic journeys are commonplace among these giant fish. Indeed, nearly a third of the recovered tags came from commercial fishers working the eastern Atlantic and the Mediterranean Sea.

Currently, the International Commission for the Conservation of Atlantic Tunas (ICCAT) considers the eastern and western tuna populations as separate management units. Because the western Atlantic breeding populations have been declining over the past few decades, the fishing quota for nations that fish this unit has been set considerably lower than the quota for eastern Atlantic tuna fishing. But the new research indicates that the western populations are vulnerable to pressure from all Atlantic bluefin tuna fisheries. "Our results demonstrate that bluefin tuna are capable of ranging widely throughout the North Atlantic without regard to the stock boundary in the mid-Atlantic," Block notes. "That means efforts to bring about a recovery of bluefin tuna populations will require increased cooperation among all nations fishing for bluefin tuna."

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