Spatial and Temporal Changes in the Growth Patterns and Survival of Hokkaido Chum Salmon Populations in 1970-2001

摘要

The survival strategies of Pacific salmon (Oncorhynchus spp.) offer a useful framework for quantifying both inter- and intra-specific interactions and also climate-related risk factors around the North Pacific Rim. The annual growth patterns of adult chum salmon (O. keta) returning to the Ishikari River were estimated with the back-calculation method based on scale analysis. Their growth increased during the first year in the Okhotsk Sea in the 1990s. The growth in the first year was negatively correlated with the sea ice concentration in winter, and positively correlated with the sea surface temperature (SST) during summer and fall in the Okhotsk Sea, despite the lack of a relation between SST and zooplankton biomass. The positive correlation between the growth in the Okhotsk Sea and survival was also observed in Hokkaido chum salmon. In the Bering Sea, the relationship between residual carrying capacity and growth patterns of Hokkaido chum salmon indicated that the growth reduction is affected by changes in population density-dependence. Results of stepwise multiple regression analysis of the survival rate of Hokkaido chum salmon population on body size at release from the hatchery and growth in the Okhotsk Sea showed that chum salmon have periods of critical mortality in the early marine period and the first winter at sea.