Data from the tagged fish have revealed that bluefin tuna routinely swim across the Atlantic, with fish tagged off the coast of North America visiting spawning grounds in the Mediterranean and in the Gulf of Mexico. The data show that the western and eastern populations forage together on common fishing grounds, then move to distinct spawning grounds when it is time to breed. As a result, fish from both populations are affected by fisheries on both sides of the Atlantic.
The tagging data were recently confirmed using a completely different technique, based on chemical analysis of the tunas' "otoliths," or ear bones, which retain a characteristic chemical signature depending upon where the tuna was originally spawned.
A unique aspect of this study, published in the journal Science, shows that the large fish that visit the northern waters of Canada are derived primarily from the Gulf of Mexico breeding stock, and that and that there is a mixture of fish from both Gulf of Mexico and Mediterranean stocks in waters along the U.S. continental shelf.
The electronic tags have also revealed these giant tuna dive to depths of nearly a mile and range through waters from the tropics to frigid polar seas. They can do so because bluefins are among the rare ocean animals that have the capacity to maintain a warm, stable body temperature throughout their wide thermal niche much like a mammal or bird.
TAG data have also helped to uncover where, when and how bluefin tuna spawn, at what age they mature, and are helping to increase the accuracy of population estimates for Atlantic bluefin tuna.
The 1,000th tag is riding on the back of a bluefin tuna, recording its every move. Of the 1,000 tags deployed since 1996, approximately half have been recovered or reported back, documenting more than 21,000 days of tuna behavio
|Contact: Randy Kochevar|
Tag-A-Giant Foundation (The Ocean Foundation)