Global Warming Effect on Life History and Population Dynamics of Japanese Chum Salmon

We revealed the effects of long-term climatic/oceanic condition on growth, survival, production dynamics and distribution of chum salmon (Oncorhynchus keta) using path analysis and prediction method based on the SRES-A1B scenario of the IPCC. Variability in growth of chum salmon at age-1 to -4 was estimated based on the back-calculation method using scales of 4-year-old adults returning to the Ishikari River of Hokkaido Island in Japan during 1945-2005. Hokkaido chum salmon had higher growth rates at age-1 since the late 1980s. Path analysis indicated that the growth at age-1 in the Okhotsk Sea was directly impacted by warmer sea surface temperature (SST) associated with global warming. The increased growth at age-1 resulted in higher rates of survival and larger population sizes. In the Bering Sea, the large population sizes led to decreased growth at age-3 and indirectly smaller fork length of adults because of density-dependent effect. Prediction about the global warming effect on chum salmon based on the SRES-A1B scenario of the IPCC resulted that (1) the global warming will affect decrease in carrying capacity of chum salmon for reducing their distribution area, (2) strong density-dependent effect will occur in populations, and (3) Hokkaido chum salmon will lose migration route to the Sea of Okhotsk.