Bluefin tuna swim too far - at their peril

In the mid-1960s, fishermen were quick to grab the economic lure. North Atlantic bluefin catches peaked at that time at about 35,000 metric tons. But then, eight years later, overfishing sent the catch plummeting to 15,000 metric tons. In the western Atlantic, the catch fell from a '64 peak of 20,000 metric tons to 6,100 metric tons in the late 1970s.

In response, ICCAT's 22 member countries divided the Atlantic into eastern and western sections, each with its own quota.

The idea of drawing a line down the middle of the Atlantic was based more on politics than on science, contends Richard Ruais, executive director of the East Coast Tuna Association, an industry group in Salem, N.H. Fishermen long observed that bluefin travel throughout the Atlantic, he says, and some early tracking studies showed the same results.

But others held that the location of two known spawning grounds - the Gulf of Mexico and the Mediterranean - indicated that two separate populations existed. In arguing for separate quotas, they also pointed to different average sizes and ages at maturity among eastern and western bluefin. Just as important, they cited competing evidence that the two populations rarely mixed.

As a result, the US, Canada, and Japan were allowed to land a combined 2,500 metric tons a year in the western Atlantic, Mr. Ruais says. The Europeans, meanwhile, have a quota of roughly 40,000 metric tons a year in the east.

But the research from Block and Dr. Lutcavage indicates that the populations aren't as separate as some believed. "The two-stock hypothesis and plan is not a very safe way to protect bluefin tuna, when up to 30 percent of the bluefin you tag off New England migrate across the Atlantic," Ruais says. Previous estimates had put mixing of the two populations at only 2 to 4 percent.

As if to add another wrinkle, Lutcavage's work suggests that the bluefin may have a third spawning ground in and around the Saragasso Sea. The evidence, she acknowledges, is inconclusive at the moment. But if further studies confirm the initial results, Mr. Schmitten of the National Marine Fisheries Service holds that ICCAT will have to curb fishing in that area, too.

For his part, Ruais holds that the studies' data argue for a regime that would allow US fishermen to increase their catch, while their eastern counterparts "need to do their fair share."

"We will expect payback" at the ICCAT talks in November, he says.

But such talk troubles Carl Safina, of the National Audubon Society's Living Oceans program. He suggests that before western quotas are relaxed, people need to take a hard look at what the 30 percent migration figure really means.

"The higher percentage of fish associated with the eastern Atlantic," he says, could be fallout from disturbances in the populations to the west."

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