A fish bioenergetics model of Japanese chum salmon (Oncorhynchus keta) for studying the infulence of environmental factor changes

Abstract

In the 1990s, a reduction of Japanese chum salmon (Oncorhynchus keta) body size was observed. In order to investigate this body size reduction of Japanese chum salmon in the North Pacific, we developed a bioenergetics model for chum salmon. Our model was based on NEMURO.FISH, using respiration and consumption terms and assumed that SST and prey zooplankton density are the determining factors of the reduction of body size. SST and prey zooplankton density are obtained from the result of NEMURO embedded in 3-D physical model, along the migration route of chum salmon. The period of foraging migration is supposed to be four years and the life stage of Japanese chum salmon is divided into eight stages, i.e. four stages for summer and the other four for winter. The model reproduced the body size of the 1972 and 1991 year classes of chum salmon, respectively. Reproduced body size of the 1972 year class was larger than that of 1991 year class. This result showed a good agreement with the observations in the Bering Sea. Moreover, our model reproduces the trend of observations in l970—2000 well. The prey density, especially in the Eastern North Pacific, had a larger influence on the change of body size than SST did. This suggested that the size reduction of Japanese chum salmon in the 1990s was partly affected by prey zooplankton density.