Radioactive bluefin tuna crossed the Pacific to US
Source: Agencies |
May 30, 2012, Wednesday
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ACROSS the vast Pacific, the mighty bluefin tuna carried radioactive contamination that leaked from Japan's crippled nuclear plant to the shores of the United States 9,650 kilometers away - the first time a huge migrating fish has been shown to carry radioactivity such a distance.
"We were frankly kind of startled," said Nicholas Fisher, a researcher reporting the findings online Monday in the Proceedings of the National Academy of Sciences.
The levels of radioactive cesium were 10 times higher than the amount measured in tuna off the California coast in previous years. Still, that's far below safe-to-eat limits set by the US and Japan.
Previously, smaller fish and plankton were found with elevated levels of radiation in Japanese waters after a magnitude-9 earthquake in March 2011 triggered a tsunami that badly damaged the Fukushima Dai-ichi reactors. But scientists did not expect the nuclear fallout to linger in huge fish because they can metabolize and shed radioactive substances.
One of the largest and speediest fish, Pacific bluefin tuna can grow to 3 meters and weigh more than 450 kilograms. They spawn off the Japanese coast and swim east at breakneck speed to school in waters off California and the tip of Baja California, Mexico.
Five months after the Fukushima disaster, Fisher of Stony Brook University in New York and a team decided to test Pacific bluefin that were caught off the coast of San Diego. To their surprise, tissue samples from all 15 tuna captured contained levels of two radioactive substances - ceisum-134 and cesium-137- that were higher than in previous catches.
To rule out the possibility that the radiation was carried by ocean currents or deposited in the sea through the atmosphere, the team also analyzed yellowfin tuna, found in the eastern Pacific, and bluefin that migrated to Southern California before the nuclear crisis. They found no trace of cesium-134 and only background levels of cesium-137.
The results "are unequivocal. Fukushima was the source," said Ken Buesseler of the Woods Hole Oceanographic Institution.
Now scientists want to track other migratory species including sea turtles, sharks and seabirds for radiation.
"We were frankly kind of startled," said Nicholas Fisher, a researcher reporting the findings online Monday in the Proceedings of the National Academy of Sciences.
The levels of radioactive cesium were 10 times higher than the amount measured in tuna off the California coast in previous years. Still, that's far below safe-to-eat limits set by the US and Japan.
Previously, smaller fish and plankton were found with elevated levels of radiation in Japanese waters after a magnitude-9 earthquake in March 2011 triggered a tsunami that badly damaged the Fukushima Dai-ichi reactors. But scientists did not expect the nuclear fallout to linger in huge fish because they can metabolize and shed radioactive substances.
One of the largest and speediest fish, Pacific bluefin tuna can grow to 3 meters and weigh more than 450 kilograms. They spawn off the Japanese coast and swim east at breakneck speed to school in waters off California and the tip of Baja California, Mexico.
Five months after the Fukushima disaster, Fisher of Stony Brook University in New York and a team decided to test Pacific bluefin that were caught off the coast of San Diego. To their surprise, tissue samples from all 15 tuna captured contained levels of two radioactive substances - ceisum-134 and cesium-137- that were higher than in previous catches.
To rule out the possibility that the radiation was carried by ocean currents or deposited in the sea through the atmosphere, the team also analyzed yellowfin tuna, found in the eastern Pacific, and bluefin that migrated to Southern California before the nuclear crisis. They found no trace of cesium-134 and only background levels of cesium-137.
The results "are unequivocal. Fukushima was the source," said Ken Buesseler of the Woods Hole Oceanographic Institution.
Now scientists want to track other migratory species including sea turtles, sharks and seabirds for radiation.
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