Pacific bluefin tuna transport Fukushima-derived radionuclides from Japan to California

Hopkins Marine Station, Stanford University, Pacific Grove, CA 93950; and b
School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook,
NY 11794

Daniel J. Madigana, Zofia Baumann, and Nicholas S. Fisher - approved April 25, 2012 (received for review March 22, 2012)

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. We measured γ-emitting radionuclides in California-caught tunas and found 134Cs
(4.0± 1.4 Bq kg−1) and elevated137Cs (6.3± 1.5 Bq kg-1) in 15 Pacific bluefin tuna sampled in August 2011. 

This paper goes into more detail, but that measurement of radiation is key.  The amount, 6.3 Bq per Kg is significantly higher than pre-Fukushima levels, yes.  HOWEVER, it is an insignificant amount of radiation.

It means that, yes, Bluefin Tuna is carrying radiation from Japan to the West Coast faster than ocean currents do the job.  But the resulting Cesium content is miniscule.

These fish were caught off San Diego in August 2011.

http://micheli.stanford.edu/pdf/Madiganetal_PNAS_2012.pdf