LOS ANGELES, CALIF.—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 kilometres 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, one of the researchers 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. But even so, that’s still far below safe-to-eat limits set by the U.S. and Japanese governments.
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 that sail the world because such fish can metabolize and shed radioactive substances.
One of the largest and speediest fish, Pacific bluefin tuna can grow to 3 metres and weigh more than 450 kilograms. They spawn off the Japan coast and swim east at breakneck speed to school in waters off California and the tip of Baja California, Mexico.