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See Inside March 2010

The Deadliest Catch: A Proposed Trade Ban Could Take Bluefin Tuna off the Menu

New DNA "fingerprint" techniques could aid this month's push for an international trade ban



Jerry Driendl Getty Images

This January a 511-pound monster of a bluefin tuna sold at Tokyo’s Tsukiji fish market for $175,000—by far the highest price paid for a fish in nine years. By that afternoon, customers at Kyubey, a Michelin-starred restaurant a stone’s throw from the market, were dining on the tuna’s fatty belly, or toro, the most opulent and rich cut from the most valuable fish in the world.

Japanese diners could soon face much higher bills for bluefin. This month a meeting of the Convention on International Trade in Endangered Species (CITES) in Doha, Qatar, is slated to consider a proposal to ban all commercial trade of the Northern bluefin, Thunnus thynnus, grouping it with megafauna superstars such as the white rhino and the Asian elephant. Japan imports about 80 percent of the total bluefin catch in the Atlantic and Mediter­ranean, even as those stocks have plummeted to such paltry levels that many scientists speculate that the fish could be headed for extinction.

Never before has such a commercially important animal been subject to an international trade ban, and proponents have braced for furious opposition. To qualify for a complete trade ban, CITES requires that the population of a species must have declined to less than about 20 percent of its historic population size or have suffered from an extremely high recent rate of decline. And although it is no simple task to measure the total size of a population that wanders from the Mediterranean to the Gulf of Mexico over its decades-long life span, recent scientific committees organized by the United Nations Food and Agriculture Organization and the International Commission for the Conservation of Atlantic Tunas (ICCAT) agree that the Northern bluefin meets the criteria.

Another condition of a CITES listing is that enforcement inspectors must be able to identify the tuna—a task that turns out to be almost as difficult as measuring the population. There are three species of bluefin tuna—Northern, Pacific and Southern—and even trained taxonomists have trouble distinguishing Northern bluefin from its Pacific cousin.

The problem extends all the way to the plate. Late last year a team of researchers from Columbia University and the American Museum of Natural History examined 68 samples of tuna smuggled out of sushi restaurants in New York City and Denver. They found that 19 of 31 restaurants either could not identify or misidentified the species of tuna they were serving—for example, replacing bluefin with bigeye (or vice versa). Of the nine samples of fish advertised as “white tuna,” they discovered that five were not tuna at all but rather escolar, a fish banned as a health hazard in Italy and Japan because it contains indigestible wax esters that can cause diarrhea.

Traditional DNA analysis techniques could not identify the various species of tuna; the fish are too genetically similar. Instead the researchers introduced a new approach. Conventional DNA “barcoding” techniques break apart DNA sequences into a jumbled bag of base pairs, then compare how similar the bag is to a reference bag. The new approach looks at the order of nucleotides in a DNA sequence at a specific location on the genome. The approach enables positive identification of any tuna sample—even one that is sitting on a bed of rice.

“Some sort of DNA-based identification will be a critical component for making CITES an effective regulation,” says Jacob Lowenstein, one of the co-authors of the research. “This will probably in the short term become the standard tool for regulatory bodies.” And even if the CITES proposal fails, there will still be much to enforce. ICCAT is charged with setting bluefin catch quotas in the Atlantic and Mediterranean, and by most accounts it has done a terrible job of it. “ICCAT was convened and established in the 1960s because of widespread concern by tuna fishermen over the decline of bluefin tuna,” says Carl Safina, president of the Blue Ocean Institute. “Since its inception the bluefin population has done nothing but go down.”

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