After the devastating earthquake that caused a nuclear disaster at Japan’s Fukushima Daiichi nuclear power plant in March 2011, traces of radiation are now being found in the muscle tissues of Bluefin tuna near off the coast of California. Usually such a discovery would be alarming; however, the levels that are established are too low to harm the fish or the humans consuming the fish. Consequently, the levels of radiation are high enough to allow scientists and conservationists to track and protect this species that is currently being overfished.
In the spring of 2012, Dan Madigan from Stanford University, along with his colleagues found traces of Cesium isotopes 137 and 134 in Bluefin tuna captured near San Diego. The fish most likely picked up this radiation by feeding on plankton and other small fish near the coast of Japan. Using the half-life of these radioactive isotopes, they devised a way of studying the tuna fish. Cesium 134 having a half-life of 2.1 years and Cesium 137 one of 30.1 years, allows the scientists to calculate the ratio of the two isotopes in the fish and to see how recently they have migrated to the waters near the US. In essence, the higher the ratio of two isotopes, the more recently the immigrant fish, migrated to the area it was found.
Scientists already knew that the Pacific blue-fin spawn in Japanese waters and spend their first life year foraging [searching for food] in these waters and later either staying put or migrating to Californian waters to fatten up before mating. With the help of the radioactive isotopes, Madigan and company were able to find that the fish aged 1.6 years and younger were migrants from Japan and that the trip for there to the West took them two months. This agreed with what they already knew and validated it.
Tracking Fukushima’s radioisotopes in Fish has potential in being a good tracking technology for the movement of other migratory species in the Pacific Ocean, like whales, turtles, sharks and other fish. Though Cesium 134 levels are soon going to become too little to provide accurate and sufficient information, by correlating Cesium 137 levels with other longer lived and stable isotopes such as Carbon and Nitrogen, Madigan and team created an alternative method for other scientists to use. Essentially, they found a relationship between Cesium and other radioisotopes that can be easily used in the future. His findings also proved that even the worst of situations and occurrences, can have some positive results.
Scientific American Article May 2013 : “Tailing Tuna” by Marissa Fessenden
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