Influence of Behavioral Patterns of Several Fish Species on Their Radioactive Cesium Concentrations Revealed with a Biotelemetry System After the Nuclear Accident Caused by the 2011 Great East Japan Earthquake

The Great East Japan Earthquake and subsequent tsunami on March 2011 damaged Fukushima Daiichi Nuclear Power Plant (FDNPP), and a part of radioactive materials released from FDNPP entered in coastal waters of north–eastern Japan. Fisheries Cooperative of Fukushima Prefecture has autonomously banned coastal fisheries since 15 March 2011. Japanese Government restricts foods including fishes that contain radioactive cesium (Cs) above the maximum limit of 100 Bq kg−1. Given this serious situation, we have studied whether fishes can transfer radioactive materials to other areas. For this purpose, we selected seven target fish species containing relatively high concentrations of radioactive Cs measured by authorities and monitored their behaviors around rocky beds in the open sea and in a port near the coast off Fukushima Prefecture. The monitoring was performed by an ultrasonic biotelemetry system consisting of fixed receivers and pingers inserted in fish. The results revealed two types of behaviours: site fidelity and migration. Fish species with high concentrations of radioactive Cs preferentially indicated the site fidelity over the migration. A decline of radioactive Cs concentrations in fish may be attributed to a natural decrease overtime and a replacement of contaminated individuals by immigrant ones with a low concentration of radioactive Cs from less contaminated waters.