Radiocesium concentration of small epipelagic fishes (Sardine and Japanese Anchovy) off the Kashima-Boso Area

Abstract

After the Fukushima Dai-ichi Nuclear Power Plant (FNPP) accident, which occurred in March of 2011, the National Research Institute of Fisheries Science (NRIFS) undertook emergent radioactivity monitoring of 63 samples of small epipelagic fishes (such as sardine and Japanese anchovy) collected by commercial fishery boats off the Kashima-Boso area (located to the south of the Fukushima coast) from 24 March 2011 to 21 March 2013. Fluctuations in the radiocesium concentration in fish muscles synchronized with the decreasing concentration from seawater near the fishing ground; the radiocesium concentration in fish muscles reached a maximum of 31 Bq/kg-wet in July 2011, after which it declined gradually. From 2012 to 2013, the radiocesium concentrations in fish muscles were low (0.58–0.63 Bq/kg-wet). Compared to the 137 Cs concentration before the FNPP accident, 137 Cs concentration in fish muscles in 2013 was still about 10 times higher, whereas it was about 4.5 times higher in seawater near the fishing ground in 2012.