Pacific bluefin tuna have transported radioactivity released by the nuclear plant damaged by the tsunami in Japanlast year to the coast of California, 6,000 miles away, according to a report just released.
In an article published this week in “Proceedings of the National Academy of Sciences,” Daniel J. Madigan, Zofia Baumann, and Nicholas S. Fisher report that traces of cesium-137 and cesium-134 found in the flesh of 15 tuna near San Diego in August 2011 can have no other source than the Fukushima Dai-ichi reactors that were damaged in March, 2011 by the tsunami.
In the Abstract the researchersstate: “ The Fukushima Dai-ichi release of radionuclides into ocean waters caused significant local and global concern regarding the spread of radioactive material. We report unequivocal evidence that Pacific bluefin tuna, Thunnus orientalis, transported Fukushima-derived radionuclides across the entire North Pacific Ocean.”
The fish,15 tuna averaging about 15 pounds each, were of a size that would have left Japanese waters about a month before their capture. Bluefin tuna spawn in the Western Pacific, then travel east where they feed and fatten in the nutrient-rich upwellings that occur along the California coast.
According to lead-researcher Madigan, the levels measured in the fish were about 3 percent higher than naturally occurring levels of radioactivity in tuna. Hefurther speculated that much higher levels of cesium 134 were likely present in the bluefin tuna immediately following the reactor failure, perhaps as much as 40 to 50 percent higher. Cesium 134 decays quickly, with a half-life of twoyears. The level of radioactive material detected was far less than the Japanese safety limit. What came as a surprise is the nuclear material remained in the fish’s bodies, as they are known to metabolize radioactivity and shed it as they grow.
The study in far from over, and will continue with additional tuna sampling as well as the monitoring and testing of other migratory animals and fish.