When Japan’s Fukushima Dai-ichi power plants were damaged by an earthquake and subsequent tsunami in 2011, it was considered historically the largest accidental release of radioactivity into global oceans1. After this disaster, speculation arose that radionuclides released into the pacific might be contaminating migratory marine mammals. Early in 2011, through funding from our Science and Environmental Conservation programs, we funded researchers who were focusing on what the Fukushima release might mean for marine life. Two pieces resulting from their investigations have just been published: a paper in Environmental Science & Technology showing the sharp decline over time in radioactive cesium levels in tuna and other marine organisms in the Pacific, and a Perspective in Science summarizing findings related to Pacific bluefin tuna migrations.
“This research answered two big questions we had set out to answer,” explained lead author Daniel Madigan, who is currently the Director of Research at the Vizcaino Research Laboratory in Santa Rosalia, Mexico. “First, would Fukushima radioactivity work as a way to trace migration patterns of species like Pacific bluefin tuna? Second, did the radioactivity in these species translate into dangerously high levels, or any levels at all, of contamination for human consumption?”
The answer to the former is yes; to the latter, no. The trace amounts of radioactive cesium in fish were effective for tracking the migration routes of Pacific bluefin tuna. However, those trace amounts did not make their way into tuna, sharks, dolphins or other big predators in the central and eastern Pacific. In other words, the radioactive cesium was not accumulating in marine species as a contaminant of concern for human consumption, but still proved to be a useful chemical tracer when applied to the right species.
The Fukushima radioactivity also worked as an effective chemical tracer over a short period of time, but by using it, the scientists were able to develop another similar tracer that will function for a longer period of time. The tracers revealed that more Pacific bluefin tuna migrate to the east than previously believed, providing important implications about how we should assess the regional impacts of fishing and make management recommendations.
As noted by the researchers, samples of 91 different animals in the waters off the coasts of Japan, Hawaii, California and Mexico uncovered no trace of Fukushima radioactivity. Ultimately, these chemical tracers – manmade contaminants – have been double-edged swords: they can cause valid public concern when levels are high, but they can also uncover new information about ocean ecosystems and life within them.
Find the abstracts: