- Comparative ecology of latitudinal difference in population dynamics in clupeid fishes ?
Among 15 clupeid species distributed in the waters around Japan, the northern-most subarctic species herring Clupea pallasii was observed to have large fluctuations in recruitment within and between spawning seasons. In blue sprat Spratelloides gracilis, on the other hand, growth and recruitment were stable within a spawning season and between years. The large population fluctuation in herring and stable population in blue sprat are considered to stem from these latitudinal differences in recruitment dynamics.

Main carnivorous zooplankton living in the ocean, is chaetognatha, amphipoda and jellyfish. Especially, the role of chaetognaths and jellyfish having high biomass in the epipelagic ecosystem, are important as the predator of many commercial fish larvae. Distribution, life history and feeding of pelagic chaetognaths were studied in coastal waters of Japan, the Sea of Japan and Alaska Bay to establish the ecosystem model in the marine food web.

- Egg and Larval transport mechanism in the subtropical circulation -
Focusing on the Japanese eel, larval transport mechanism in the North Equatorial Current, and effect of global oceanic fluctuation with time-scale of a few years to ten few years on the glass eel abundance were clarified quantitatively on the basis of numerical simulations and statistic analyses.

- Human activities disturbed the marine environment -
We study marine pollution by hazardous chemicals such as organochlorine compounds (PCBs,DDTs, BHCs, etc.), organotin compounds (TBT, DBT, MBT) , heavy metals (Hg, Cd, Pb, etc.) and radionuclides (Pu, Cs, etc.), and their biological impact using several bio-indicators (dolphins, seals, caprellid species, etc.). We intend to make clear the present marine pollution in global scale, to investigate biological impact in the sea, and to elucidate mechanism of hazardous chemicals in the world.

Because the Japanese Archipelago covers sub-tropical to sub-arctic climate zones, coastal environments greatly change with latitude. Temperate coastal fish species, which are widely distributed from Kyushu to Hokkaido, may have diversified life patterns due to adaptation to different environmental conditions even in the same species. These eco-physiological differences in local populations of same species may result in differences in recruitment mechanisms between areas such as northern and southern Japan. We are studying latitudinal effects on the early life ecology and subsequent recruitment mechanism mainly focusing on the Japanese flounder Paralichthys olivaceus.

By employing field and laboratory studies, our laboratory is working on fish survival during early life history. Ecological approach to a population of Japanese seabass in Ariake Sea revealed the presence of “continental relict” ecosystem and its indispensable contribution to the survival of endemic species in this area. From laboratory study, the significance of developmental speed was pointed out for the metamorphic success of flatfishes, suggesting the possible modulation of survival rate in the sea by environmental fluctuations.

The goal of our “laboratory of fish psychology” is to scrutinize behavioral ontogeny in marine fishes with emphasis on their survival strategy. Chub mackerel Scomber japonicus, jack mackerel Trachurus japonicus and red sea bream Pagrus major are major target species. Interactions between fish larvae and jellyfish are also studied in the natural waters of Wakasa Bay off Kyoto as well as in the laboratory.