Researchers have found tiny amounts of radioactive cesium in albacore caught off Washington and Oregon. The radiation, originating from the 2011 tsunami in Japan, is thought to pose no public-health risk, but it is allowing scientists to track the migratory patterns of tuna for the first time.

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Since the early 1950s, scientists have argued about one of the West Coast’s most popular fish — albacore tuna.

Are the silvery streaks that tempt thousands of anglers each year part of one family of highly migratory fish? Or are there really two groups of speedy tuna, each traveling a different route around the sea?

Now this half-century-old argument could be clarified by a disturbing new pollutant: radioactive isotopes from Tokyo’s Fukushima Daiichi nuclear power plant.

Oregon State University researchers and federal scientists are finding exceedingly tiny amounts of radioactive cesium in albacore caught off the coast of Washington and Oregon. And it’s clear the radionuclide originated with the nuclear accident that followed the deadly tsunami that hit Japan in March 2011.

While some forms of cesium persist in the environment for decades, one isotope scientists saw, cesium-134, has a half-life of a little more than two years and could only have come from that accident.

So far, the trace amounts that OSU scientists found in tuna are far less than anything that would pose a risk to humans; a fish eater would have to consume several thousand pounds of the most radioactive albacore they discovered just to increase by 1 percent the amount of radiation they’re exposed to from everyday sources.

“The amounts they found were incredibly small,” said Donn Moyer, spokesman for the Washington state Department of Health, which also tested the same samples and came up with the same results. “There’s nothing really remarkable about the amounts.”

But because cesium decays so quickly, the discovery makes clear that fish caught in Northwest waters picked up the radiation while feeding on smaller fish in or around Japan.

“We’re talking about barely, barely detectable levels,” said Jason Phillips, who led the work while a graduate student at OSU’s College of Earth, Ocean, and Atmospheric Sciences. “But because the radiation has to be derived from Fukushima, they had to pick it up within its vicinity or in the drift.”

For most of the 1950s, researchers tagged North Pacific albacore and determined that the fish along the West Coast traveled between here, Japan and California and Mexico.

But in the 1970s researchers began to see signs that suggested some of the California fish might be part of a different population.

“It turns out there may be two different populations,” said Richard Brodeur, with the National Marine Fisheries Service. “Ours up here might be completely different from those down off of California.”

But the fast travel so far and fast — between 50 and 200 miles in a day — that tracking their movements is almost impossible, and no one has been able to confirm their theory.

After the Fukushima disaster, Phillips and Brodeur and another graduate student in radiation health had an idea: Why not map migration routes for West Coast tuna using the radioactive fish?

So far they’ve tested 18 Northwest fish, and the results are consistent: Fish caught before the tsunami are radiation free; fish caught afterward contain trace amounts of cesium.

But the real test is yet to come. The scientists have been collecting dozens of albacore from fishermen off the California coast. They plan to test those fish soon. If those don’t show the same traces of cesium-134, it would suggest that they didn’t travel to the same place as the Northwest fish.

Understanding when and where albacore travel can help scientists protect stocks of a West Coast fish worth tens of millions of dollars annually.

The researchers are presenting their findings to a conference in Italy this weekend.

Craig Welch: 206-464-2093 or On Twitter @craigawelch.