The TAG team's research has shown that bluefin tuna tagged in the West Atlantic are composed of two populations, one that forages in the North Atlantic and moves primarily into the Mediterranean Sea to breed, and another that tends to swim on the North American side of the ocean while spawning exclusively in the Gulf of Mexico.
Genetic analyses conducted by marine biologist Andre Boustany and research associate Carol Reeb, both members of Block's team at Hopkins Marine Station, confirmed that the two North Atlantic populations are genetically distinct.
Block learned something else as well.
"Our tagging and genetic data reveal that while there are separate bluefin tuna populations, significant mixing exists across the North Atlantic," she said. Mixing takes place in foraging areas in the western, eastern and central Atlantic; the central region had long been thought to be a no man's land that separated the two fisheries.
The mixing of the tuna populations on feeding grounds is raising serious questions about current fisheries-management practices-and raising concerns about how many Gulf of Mexico-spawned fish are actually left.
Bluefin tuna are managed by the International Commission for the Conservation of Atlantic Tunas that meets yearly to set fishing quotas and determine stock assessments. In the face of a steep decline in the West Atlantic fishery, in 1982 the commission established a boundary between the fisheries at the 45th meridian. It then set separate quotas on the allowable catches for the West and East Atlantic fisheries that were supposed to hold the annual catch to a sustainable level.
Although the West Atlantic fishery seemed to stabilize in the mid-1990s at a low level,
it has been decreasing since 2000, and U.S. fishermen have not been able to catch their
modest quota. At the same time, the eastern Atlantic and Mediterranean fishing effort has
|Contact: Louis Bergeron|