Researchers have found radioactive bluefin tuna off the coast of California that were contaminated by last year’s Fukushima Daiichi nuclear plant disaster in Japan. The discovery marks the first time radiation from the disaster has been found in fish that migrated into California waters. Researchers say the levels of radioactive cesium in the tuna are 10 times higher than normal, but they said the amounts are still below levels considered unsafe for humans. The ocean off Japan was contaminated last year after thousands of tons of seawater were used to cool reactors in an attempt to prevent a total nuclear meltdown following an earthquake and tsunami.