Bluefin tuna swim too far - at their peril
Prized fish move around the Atlantic more than was thought, raising questions about need for global quotas.
On both sides of the North Atlantic, few denizens of the deep command more respect - and none fetches higher prices dockside - than the mighty bluefin tuna. Its meat graces sushi and sashimi platters in restaurants from Tokyo to New York.
For some 20 years, Atlantic bluefin have been hauled out of the sea at unsustainable rates, marine scientists say, despite international attempts to limit the catch by establishing separate fishing quotas for the eastern and western Atlantic.
Now, fresh research on bluefin migration suggests that unless governments change their view of bluefin stocks and begin to treat them as one population, overfishing - particularly on the European side of the Atlantic - could torpedo the North Atlantic bluefin.
For five years, a team led by Stanford University marine biologist Barbara Block used a set of high-tech tags to monitor bluefin movements. The study, which shed light on a number of tuna traits, confirmed that populations in the western and eastern Atlantic mixed to a much larger degree than previously believed.
This observation, other researchers say, undercuts a key premise behind the current conservation scheme and raises the prospect that continued overfishing in the eastern Atlantic could offset any gains from the tight quotas that exist for the western Atlantic.
Maintaining bluefin stocks at a level that allows for the maximum sustainable catch "will require increased cooperation among all nations fishing for bluefin," says Dr. Block, whose team reports its results in today's edition of the journal Science.
Her team's work, along with recent studies headed by New England Aquarium staff scientist Molly Lutcavage, are expected to add kerosene to a smoldering transatlantic debate over the adequacy and fairness of current bluefin quotas.
In November, the Madrid-based International Commission for the Conservation of Atlantic Tuna (ICCAT), which established the current quota regime, meets to review its conservation approach. In addition, next month the commission's scientific advisory panel is scheduled to hold an unusual midyear meeting to weigh the impact of recent studies on estimates of bluefin-tuna stocks in the North Atlantic.
The concern over bluefin is part of growing worries worldwide about humanity's impact on fisheries - vital sources of food for a burgeoning population. "Some 60 percent of the world's fish stocks are overfished or fully utilized," says Rolland Schmitten, former director of the US National Marine Fisheries Service and now head of its habitat-conservation office. He adds that in a majority of cases for the remaining 40 percent, governments lack enough information to determine the status of the populations.
For its part, North Atlantic bluefin tuna have been prized as a source of food for millenniums. Their biggest draw for fishermen today, however, is their street value. Last January, for example, a 444-pound bluefin fetched $175,000 at a seafood auction in Tokyo's famed fish market.
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."