An Ecopath model for the demersal marine ecosystem (46 functional groups) was constructed based on fisheries resources survey data and commercial fisheries catch statistics in the northern district of northeastern Japan. This is the first Ecopath model for demersal marine ecosystems in the sea area around Japan. We used outputs of the Ecopath model and network analysis tools to quantitatively describe the food web structure and examine the fisheries impacts on the ecosystem. Macrobenthos, mesopelagic fishes, and Pacific krill Euphausia pacifica were identified as important prey species, but prey selectivity of these species differed by predators. Keystone functional groups were demersal sharks, Pacific cod Gadus macrocephalus (2+years), and giant grenadier Coryphaenoides pectoralis. In primary production required (PPR%), Danish seine-trawl fishery was lower than pair-trawl fishery, whereas in relative loss in production (L-index), Danish seine-trawl fishery was higher than pair-trawl fishery.

We studied the variation of recruitment per spawning of the tiger puffer Takifugu rubripes in Ise and Mikawa Bays, Japan with special reference to temperature and salinity for clarifying the controlling factors of its interannual variation from 1993 to 2012. Interannual variation in the recruitment per spawning is positively correlated with the 10 m-depth temperature in the central area of Ise Bay in February, 5 m-depth salinity in the central area in March and 10 m-depth salinity in the bay head in April, and negatively correlated with the 30 m-depth temperature in the central area in July. On the basis of the results in a stepwise multiple linear regression analysis, we hindcast the recruitment per spawning from 1993 to 2012 using the temperature and salinity around Ise Bay.

Many studies reported that the catch of yellowtail species increased largely in the waters around northern Japan, particularly in the northern boundary of yellowtail distribution under the warm regime after 1990’s; whereas only a few studies focused on the catch in the water around Kagoshima, southwestern Japan and the southern boundary of the distribution. In this study, the catch fluctuations of yellowtail species in the water around Kagoshima have been analyzed and compared with those around Japan. We calculated the geographical center of yellowtail species catch and examined it’s relationships with regime shifts, sea surface temperature (SST) fluctuations, and catch fluctuations. The results indicate there was a significant negative correlation between the long-term fluctuations of catch in Kagoshima and Japan excluding Kagoshima (p<0.001), and the former increased (decreased) with the decrease (increase) in the latter with 4 years lag. It shows that the geographical center of the catch shifted northeastward with the increase in the SST in the mid latitudinal zone of Japan. The geographical center of the catch shifts southwestward (northeastward) in the cold (warm) regime, suggested that the fluctuations in the geographical center of the catch correspond well with regime shifts. Accordingly, the contrary trends in the catch between Japan and Kagoshima were interpreted as resulting from the changes in the distribution of yellowtail in responding to environmental SST fluctuations.