Science News

Throwback: Tracking Pacific Bluefin Tuna

A couple of years ago I wrote a copy story for an internship about tracking Pacific bluefin tuna. As I moved on to other internships then eventually Shark University, the story got buried under a stack of new stories (figuratively, of course), remaining unpublished! So today I post it even though the news is terribly old:

This copy story was written May 2013 for an internship in science communication

Thousands of Pacific bluefin tuna journey to California from the Japanese coastal waters each year in search of food before returning to their birthplace to reproduce. But the actual path of this two-month trans-Pacific migration is a mystery to scientists.  It’s difficult to tag and track youth of the warm-blooded predator, but a recent disaster made it possible to trace them from birth – the Fukushima reactor incident of March 2011 that plunged radioactive elements into the Pacific Ocean.

Nearly two years after the Fukushimi Daiichi power plant suffered critical failure when a devastating tsunami hit the coast of Japan, scientists are still finding trace amounts of radioactive material in Japanese born fish that have migrated to California. While the materials – or radioisotopes – are nonthreatening to the consumers of the sushi-grade fish, they make the tuna easy to follow on their ways to California, similar to how doctors use radioactive dye to visualize nerve tissue and organs in nuclear medicine.

Pacific bluefin tuna are born in the Pacific Ocean surrounding Japan and other nearby islands. After a year of foraging these waters, some of the fish migrate eastward to California. Frequently, scientists tag adult tuna electronically to track their behaviors; however, adolescent tuna are more difficult to tag, leaving many of their habits to mystery. Researchers at Stanford’s Hopkins Marine Station in Pacific Grove, California believe the radioisotopes can provide reliable means of mapping tuna trans-Pacific migration patterns, providing new information to thwart overfishing of the industry-popular species.

Bluefin tuna are specifically sought by global commercial industries for sushi, worth up to $1.76 million per fish to interested buyers. While the species is not endangered, it is vastly overfished, and its worldwide numbers have depleted by up to 96 percent according to a December report. By enabling scientists to track the tuna more precisely, the trace amounts of nonthreatening radioisotopes left over from the Fukushima disaster will help legislators re-map regulations to thwart commercial overfishing.

For more information on the Pacific bluefin tuna, visit


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