Climate forcing and the Kuroshio/Oyashio ecosystem

Abstract Yatsu, A., Chiba, S., Yamanaka, Y., Ito, S-I., Shimizu, Y., Kaeriyama, M., and Watanabe, Y. 2013. Climate forcing and the Kuroshio/Oyashio ecosystem. – ICES Journal of Marine Science, 70: 922–933. The Kuroshio and Oyashio, western boundary currents in the North Pacific, greatly influence climate, ecosystems, and fisheries in the western North Pacific and its adjacent waters. The Kuroshio/Oyashio ecosystem (KOE) shows interannual and decadal variability including regime shifts. Under a collaboration of the Climate Forcing and Marine Ecosystem Response (CFAME) Task Team and Working Group 20 (Evaluations of Climate Change Projections) of PICES, we analysed the observed time-series of physics, nutrients, chlorophyll, zooplankton abundance and phenology, and productivity, biomass, and catch of commercially important species to assess the impacts of Intergovernmental Panel on Climate Change's global change scenarios on KOE. Mechanistic linkages from climate forcing to fish population dynamics were explored for the Japanese common squid (Todarodes pacificus), Japanese sardine (Sardinops melanostictus), walleye pollock (Theragra chalcogramma), and chum salmon (Oncorhynchus keta). Future scenarios of zooplankton, commercial species, and ecosystem changes were presented based on the empirical mechanistic linkages and results of projections for physical conditions and primary production in KOE derived from both empirical knowledge and three-dimensional ecosystem-biogeochemical models. Associated data gaps, uncertainties, and implications for managers were also discussed.