Schools of Pacific bluefin tuna (Thunnus orientalis) that swam through radioactive waters off Fukushima, Japan, have made it to the coast of California, demonstrating the importance of these migratory animals as transport vectors of radionuclides. These tuna have detectable levels of the radioactive isotope cesium that scientists deem as safe for human consumption. The tuna, according to the scientists were contaminated with radiation stemming from the nuclear plant meltdown that occurred after Japan was struck by a tsunami last year following the March 11, 2011, Tohoku earthquake. The detection of radiation in 15 tuna occurred as scientists were studying migratory patterns of bluefin tuna.
According to a study published in the May 29, 2012, Proceedings of the National Academy of Sciences, recreational anglers in San Diego gave marine ecologist Daniel J. Madigan 15 tuna that were caught off San Diego, California, in August 2011. Madigan, the lead author of the study, tested a single specimen that turned out to be positive for radioactivity. Madigan then sent the 15 fish to Nicholas Fisher, a Stony Brook University marine scientist known as a specialist in radiation hazards, who tested all 15 fish. The tests revealed that the tuna were positive for two types of radioactive cesium: cesium-134 and cesium-137. These radioactive isotopes, the study said, do not occur in nature. They occur after a nuclear explosion or similar event. Cesium-137 becomes harmless after 1,000 years, while cesium-134 is a shorter-lived isotope, which bolstered the scientists’ claim that the tuna were indeed exposed to radiation from the Fukushima Nuclear Plant.
The Pacific bluefin tuna is a pelagic, fast-swimming fish that can be found in the western and eastern North Pacific Ocean. They can grow to 10 feet in length and weigh up to 1,200 pounds. An overfished species, the Pacific bluefin tuna spawn in the western Pacific off Okinawa and the Philippines, as well as in the Sea of Japan, with some staying in Japanese waters while others migrate east to the California Current. An unusual fact about this species is that it is warm-blooded. They are known to heat their bodies as much as 11 degrees Fahrenheit warmer than the waters in which they swim.
The complete study, which was funded by The Gordon and Betty Moore foundation, can be found in PDF format here.