The effect of climate change on the growth of Japanese chum salmon (Oncorhynchus keta) using a bioenergetics model coupled with a three-dimensional lower trophic ecosystem model (NEMURO)

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From the 1970s to 1990s, a reduction in the body size of Japanese chum salmon(Oncorhynchus keta) was observed. To investigate this body size reduction in the NorthPacific, we developed a bioenergetics model for chum salmon coupled with the resultsfrom a lower trophic ecosystem model embedded into a three-dimensional global model.In the bioenergetics model, respiration and consumption terms are assumed to befunctions of water temperature and prey zooplankton density, which are the determiningfactors of the reduction of body size. The model reproduced the body size of the 1972and 1991 year classes of chum salmon. The reproduced body size of the 1972 year classwas larger than that of 1991 year class, and this result agrees with observations from theBering Sea. Our model also reproduced the body size trend from l970 to 2000. The preydensity, especially in the eastern North Pacific, had a greater influence on the change ofbody size than did the SST. This suggests that the size reduction of Japanese chumsalmon in the 1990s was partly affected by changes in prey zooplankton density. In thecontext of the global warming scenario, we discuss changes in the migration route ofchum salmon and predict that the population of Japanese chum salmon experiencesignificant declines over this century.