Tuna carry Fukushima radiation to California

The levels might not be high enough to harm you if you tucked into a tuna sandwich, but some tuna are still carrying radioactive caesium from the leak at the Fukushima Daiichi plant last March. Researchers hope that similarly low levels of radiation in turtles, sea birds and sharks will allow the migration patterns of little-studied species to be tracked.

Daniel Madigan, a marine biologist at Stanford University in California, was already studying how Pacific bluefin tuna (Thunnus orientalis) migrate across the Pacific Ocean when the Japanese tsunami put a new twist on his experiment.

The leak at the Fukushima Daiichi reactor released caesium isotopes into the Pacific, and fish can pick up the radioactive material from the water they swim in and from the food they eat.

Mysterious migrations

Juvenile tuna can take between one and four months to swim the 9000 kilometres from Japan to California. The researchers measured caesium isotopes in young tuna caught off the coast of San Diego, and found detectable levels of caesium-134 in 15 fish. The isotope could not be detected in fish that were caught before 2011.

Because caesium-134 has a half-life of two years, Madigan expects that researchers will be able to find it in the long-lived fish for some time to come. Tuna migration patterns are well known, he says, but the radiation may be useful in tracking other species such as salmon sharks (Lamna ditropis). If these sharks behave as researchers suspect they do, the migratory males would carry Fukushima radiation, but the stationary females would not.

Journal reference: Proceedings of the National Academy of Science, DOI: 10.1073/pnas.1204859109

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