A nuclear disaster may lead to insights into the mysterious migrations of Pacific bluefin tuna, a fish species that recently has suffered a dramatic decline.
Scientists report in a new study that they can use trace amounts of radiation in bluefin tuna to sketch the crisscrossing passage of the fish through the world's largest ocean. Understanding how many fish move back and forth may help with the conservation of bluefin tuna.
During the Fukushima nuclear disaster, two years ago, radioactive particles flooded into the Pacific Ocean. Bluefin tuna swimming through these waters began to store certain radioisotopes, called cesium 134 and cesium 137, in their muscle tissue.
The low levels of these particles don't pose a health danger to either the fish or sushi eaters, said Daniel Madigan, a Stanford University graduate student and an author on the study in the journal Environmental Science & Technology. But scientists can track the chemical mark of Fukushima to recreate a timeline of when bluefin tuna traveled from their spawning grounds, in waters around Japan, to the coast of North America.
Until now, researchers have stuck expensive electronic tagging devices to bluefin tuna to follow their movements through the sea. But it's difficult for scientists to wrestle with a live, torpedo-shaped fish that can weigh more than 1,000 pounds.
With that technology, researchers still don't know where the fish has been before it was tagged or how many tuna are making the trip each year.
"What the chemical techniques, like radiocesium, can do is tell you where an animal came from," said Madigan, who has gathered samples from more than 400 bluefin in the past two years. Only 50 samples were used in the current study.
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