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Original data (Cs and Cs, and sampling location) of marine products in Fukushima Prefecture monitored during 2011-2015 (n = 32,492) were analyzed to present an updated detailed description of radiocesium contamination after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident and to examine taxon/habitat-specific decreasing trends in different areas. Furthermore, marine species data presented by the Tokyo Electric Power Company (TEPCO) during 2012-2015 (n = 5458) were analyzed to evaluate the decreasing trends ofCs inside and outside (within a 20 km radius) of the FDNPP port. Monitoring results by Fukushima Prefecture show that percentages of samples higher than the Japanese regulatory limit of 100 Bq kg-wet (>RL%) were higher, whereas those below the detection limit (RL% and

We estimated the radiocesium translation from contaminated sediments to benthic organisms off the coast of Fukushima. We conducted fi eld investigations and an experiment with a benthic polychaete ( Perinereis aibuhitensis ) reared on highly contaminated sediments collected from a station 1 km off the Fukushima Dai-ichi Nuclear Power Plant. Results of the fi eld investigations revealed that radiocesium contamination in benthic organisms depended on their feeding habitat. The radiocesium concentration in carnivore or herbivore feeder polychaetes was higher than that in deposit feeders. Radiocesium concentrations of all benthic organism specimens were lower than that in sediments collected from the same sampling point. Results of the rearing experiment showed that the concentration ratio (CR) of 137 Cs for P. aibuhitensis and contaminated sediments (wet/wet) was less than 0.10. Moreover, 4 days after separation from the contaminated sediments, the 137 Cs concentrations in P. aibuhitensis rapidly decreased. Based on the results of our fi eld investigations and rearing experiment, we conclude that the intake of radiocesium through the benthic food web is limited for benthic organisms, despite the high contamination of the surrounding sediments.

Although the number of marine protected areas (MPAs) for stock management has increased, movements or differences in population structure of a target species between an MPA and surrounding fishing areas have rarely been considered in stock biomass estimations. We developed a surplus production model considering seasonal movements between two areas; the model was applied to Sea Ravens Hemitripterus villosus off Fukushima, where almost all fishing has been prohibited since the 2011 accident at the Fukushima Dai‐ichi Nuclear Power Plant. We predicted future biomass by using CPUE data from coastal gill‐net fishing and offshore bottom trawl fishing in 2000 to 2009. The model reflected the seasonal coastal–offshore movements of Sea Ravens well, and it predicted increasing Sea Raven biomass in both areas, which was validated by the CPUEs observed after 2010—including those for trial bottom trawl fishing that occurred within limited offshore areas after the accident. Our results indicate that the newly developed model incorporating seasonal movements of Sea Ravens is feasible and that the waters off Fukushima have effectively been serving as an MPA since the nuclear accident. We also demonstrated the model's applicability for estimating the optimal fishing effort and designing a new MPA for stock management that considers seasonal movements. Received August 29, 2014; accepted May 4, 2015

We examined year-class-related differences in radiocesium concentrations in Pacifi c cod ( Gadus macrocephalus ) and evaluated the potential factors affecting the differences after the release of large amounts of radionuclides from Fukushima Dai-ichi Nuclear Power Plant (FNPP) in March 2011. The concentration of radiocesium was highest in the 2009 and earlier year-classes (yc) (≤2009 yc), followed by the 2010 yc, and was rarely detected in the 2011 yc. Trawl surveys throughout the year revealed that a proportion of Pacifi c cod born in or before 2009 and 2010 were distributed in the coastal area from winter to early summer, whereas all individuals were on the upper continental slope from early summer to winter. The concentration of radiocesium decreased more rapidly in the 2010 yc than in the ≤2009 yc. The diet of cod changed ontogenetically and spatiotemporally. The organisms preyed upon on the upper continental slope by cod of all year-classes and in the coastal area by the 2010 yc contained very low concentrations of radiocesium. However, some food items ingested in the coastal area by the ≤2009 yc had relatively

Monitoring and surveying of radioactivity in seawater and biota in the marine environment off the coast of Fukushima Prefecture in the Pacifi c Ocean are important for understanding the dispersion of artifi cial radionuclides after the TEPCO Fukushima Daiichi Nuclear Power Station (FD1NPS) accident. Marine biota were collected in the coastal area off Fukushima Prefecture after this accident to investigate the radioactivity of 134 Cs, 137 Cs, and 110m Ag in marine biota, including not only fi sh and shellfi sh but also benthos. It is well known that 108m Ag, one of the radioactive isotopes of Ag, was observed in some kinds of squid and octopus before this accident. As a result, 110m Ag was observed in many kinds of marine biota off the coastal area of Fukushima. It is suggested that rapid change in the radioactivity in seawater, resuspension of particles from sediments, and food chain effects led to high radionuclide activities in the marine biota after this accident. Keywords 110m Ag • 134 Cs • 137 Cs • Marine organisms

KEY WORDS: Japanese flounder, Kuroshio, larvae, transport-induced mortality.Japanese flounder Paralichthys olivaceus is a common flatfish of the coast of Japan that usually inhabits coastal waters at depths of <100 m, and spawn pelagic eggs at depths of <50 m. The larvae spend approximately 1 month in the pelagic phase, then metamorphosing larvae migrate into nearshore areas using tidal currents before settlement. 1-3 The nursery habitats of juvenile Japanese flounder are usually observed in nearshore sandy grounds at a depth of <15 m. 1