Tuesday | April 21, 2015
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Radioactive tuna from Fukushima?

LOS ANGELES — 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.






Maybe the fish could still tell their story.



“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 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.


Or that was the theory, anyway.


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 the animals ever got close enough to Fukushima to encounter its plume in the first place.

“I thought, OK, I can do this, but I wasn’t expecting anything,” Fisher said.



“He was like, ‘You’re not going to believe it, but here it is,’” Madigan said.

The tuna had tested positive for cesium-134 and cesium-37, both known waste products from Fukushima. For Madigan, it was “a real discovery moment, like in the movies,” he said.



In May, Fisher and Stony Brook postdoctoral researcher Zofia Baumann published a paper in the journal Proceedings of the National Academies of Sciences detailing their findings. The team believed it was the first time that anyone had demonstrated migratory animals could transport radioactive contaminants across the Pacific.



They concluded that their tracking method worked, and Fukushima provided “an unprecedented opportunity” for scientists to use radioactive tracers to follow animal movement.

“This was just nature being amazing,” Fisher said. “Now, potentially, we have a very useful tool for understanding these animals.”

They’re digging in to see what secrets the Fukushima cesium might reveal about other animals.

In coming months, the three researchers and colleagues at the National Oceanic and Atmospheric Administration and other institutions plan to analyze hundreds more bluefin tuna, as well as albacore tuna; mahimahi; ocean sunfish; opa; mako, blue and salmon sharks; loggerhead turtles; and sooty shearwaters, a type of migratory seabird.

They’ll examine samples collected in New Zealand, Hawaii and Alaska, as well as in California. They might look through archived specimens for salmon and whales to test. Other research groups may track the contamination to study marine animals too, Madigan said.


In salmon sharks, it’s known that males tend to congregate in the western Pacific and females in the east, with both sexes meeting up in Alaska to breed. But biologists don’t know whether the segregation is complete. If female salmon sharks test positive for cesium, that might suggest they occasionally do travel west to Japan, and Alaska may not be the only place the species goes to reproduce. That could have ramifications for conservation efforts.

Hoyt Peckham, another Stanford-affiliated marine biologist, who is based in Mexico, is sending to Fisher’s lab some samples from endangered loggerhead turtles that have died and washed up on the shores of Baja California Sur. Using the tracer to get a better idea of the timing of loggerhead migrations should help with his conservation work too.