Marine biologist Dan Madigan stood on a dock in San Diego and considered some freshly caught Pacific bluefin tuna. The fish had managed to swim 5,000 miles from their spawning grounds near Japan to California's shores, only to end up the catch of local fishermen.
It was August 2011, five months since a magnitude 9 earthquake and tsunami had struck in Japan, crippling the Fukushima Daiichi power plant. Madigan couldn't stop thinking about pictures he'd seen on TV of Japanese emergency crews dumping radioactive water from the failing reactors into the Pacific Ocean.
The graduate student looked at the tuna and wondered: Could they have transported any of that radiation to California?
For most people, the thought of radioactive sushi tuna is nightmarish, but for Madigan it represented an opportunity.
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, man-made event ? the plant failure in Fukushima ? could be linked to the lives and fates of animals making homes over half the globe.
Madigan bagged some tuna steaks he had collected from the fishermen, threw them in a cooler and made a mental note to call Nicholas Fisher, a scientist he knew who would be able to tell him whether the tuna had carried radiation from the disaster.
Maybe the fish could still tell their story.
***
Madigan began thinking about the globe-spanning migrations of marine animals in 2006, during a fishing trip in the open waters off Costa Rica.
For hours, he and his friends saw nothing ? no land, no features in the water, no fish. Then, in a flash, they hooked and released a dozen sailfish, magnificent 150-pound catches known for their spectacular jumping maneuvers and brilliant colors.
"It's black water, and all of a sudden you have a huge animal," said Madigan, a Long Island, N.Y., native who camps on the weekends and catches all of the fish he eats. "Why? Why now? And why here?"
Intrigued, Madigan enrolled in a doctoral program at Stanford University's Hopkins Marine Station in Pacific Grove, Calif., where scientists used electronic tags to track the journeys of sea creatures such as white sharks, leatherback turtles and the black-footed albatross.
They had also tagged the Pacific bluefin tuna, a creature distinguished by its unusual biology (it's one of the few warm-bodied fish) and its popularity on sushi menus. At a January auction in Tokyo, a buyer paid a record $1.8 million for just one of the fish, which are carved up into toro and other choice bites.
Pacific bluefin tuna migration is mysterious. Only some of the tuna born each year leave the Western Pacific around Japan for California, swimming for two months or more to reach their destination. They stay here for a few years, and then they swim back to the waters where they were born so that they can reproduce. Some tuna are thought to cross the ocean multiple times.
Researchers don't really understand why. It may have to do with food availability, ocean temperatures or other factors.
Madigan's doctoral research tries to fill in some of the blanks by looking for nitrogen and carbon isotopes in tissue that serve as signatures of where the fish have lived and for how long. But interpreting the chemical signatures can be tricky. If Madigan could use the radioactive signal from Fukushima to confirm the results of the chemical analysis, he realized, it might bolster his work.
Or that was the theory, anyway.
Madigan, a 30-year-old whose casual demeanor can mask the intensity he brings to his research, called Fisher about the San Diego steaks.
The marine radioactivity expert, who works as a professor at Stony Brook University in New York, doubted they'd detect any radiation in the bluefins. Surely, he thought, any radiation the fish might have picked up would have dissipated over the months it took for them to cross the Pacific. What's more, it was hardly certain that the animals ever got close enough to Fukushima to encounter its plume in the first place.
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