Reading Nuclear Clues About the Bluefin Tuna

Words by Emma Bryce

Reporter, Audubon Magazine

Published March 22, 2013

Tuna run. (Photo by Aziz T. Saltik / CC BY-NC-ND 2.0)

Every year, Pacific bluefin tuna zigzag the Pacific Ocean, hurtling from the Japanese coast where they spawn, to the California and Mexico coasts, then back to Japan to breed. Scientists have long tried to track the bluefin via electronic tags, to plot its crisscrossed network across the seas. But tagging is expensive and difficult on the gargantuan, stroppy fish. Now, scientists may have another feasible tracking method: use remnants from Fukushima’s nuclear blast.

The suggestion started as a hunch by marine biologist Daniel Madigan. In August 2011, he was surveying Pacific bluefin for sale in San Diego. Knowing the species’ route from Japan, he wondered whether the specimens before him might contain nuclear radiation traces carried from the Japanese Fukushima disaster on March 11 of that year.

Fukushima will be forever remembered as a doubly harsh event, one in which an earthquake triggered a tsunami that in turn destroyed three nuclear reactors. It prompted mass evacuation and fears of nuclear fallout that persist today. Of major concern was the blast’s impact on seafood and on the people who might consume ocean fish. This is what Madigan, a graduate student at Stanford University, began to consider in 2011.

His ruminations resulted in a recent study, published in the Proceedings of the National Academy of Sciences, suggesting that ocean researchers could use the devastation wrought by the nuclear accident to their advantage. The Los Angeles Times explains the logic:

If radiation from Fukushima was detectable, scientists might look for traces of the contamination in all sorts of amazing creatures that make epic journeys across the open seas, from tuna to sharks to turtles to birds. They might learn more about where the animals came from, when they made their journeys, and why. They might learn how a single, manmade event—the plant failure in Fukushima—could be linked to the lives and fates of animals making homes over half the globe.

For the highly endangered Pacific bluefin tuna—desired by luxury sushi-lovers, a fate that has caused a 96 % reduction in population—this could lead to a greater understanding of its migration. That, in turn, affects how fish are protected from greater decline.

Madigan is already working on it. Back in 2011, he bought several tuna steaks and sent them to a laboratory for testing. The steaks turned up positive for nuclear radiation, in the form of two radioisotope varieties present in the water after Fukushima: cesium 135 and 137. “What the chemical techniques, like radiocesium, can do is tell you where an animal came from,” Madigan told the Miami Herald. Hence, the analysis proved the tuna’s source and suggested that radiation could be used to trace fish migrating to and from Japanese shores. If, for instance, “the fish in the east are an important portion of the fish that go back to spawn, then we need to protect (that) group of fish,” Madigan told the Herald.

Madigan maintains the levels of radioactivity in the bluefin he sampled aren’t harmful to humans. Others, however, suggest that it could be and call for greater analysis—especially because Madigan’s research sampled just 50 fish.

Shana Miller, science adviser to The Pew Charitable Trusts said to the Miami Herald that as far as she knows, his research presents “the first detailed information on when the fish leave Japan.” Ultimately, every little bit helps—despite the need for more sampling. “We’re dealing with a severely overfished species that has little management in place right now,” she said.

Madigan’s research sheds some light on a somewhat mysterious fish, and his techniques could also come in handy with tracking other species like turtles and whales. “This is an example of how events don’t happen in a vacuum,” he said to Stanford News, “These tuna carried this radiation across the entire Pacific, the largest ocean on the planet.”