An ecosystem-based bioenergetics model was used to investigate the responses of Pacific saury (Cololabis saira) to global warming. The model was forced by the projected sea surface temperature (SST) generated by climate models that formed the bases for the Intergovernmental Panel on Climate Change fourth Assessment Report (IPCC-AR4). Twelve climate models, which reproduced the Pacific Decadal Oscillation well compared with observations, were selected and B1, A1B, and A2 emissions scenarios were used. In total, 33 ensemble simulations were conducted, of which 24 (73%) showed a decrease in wet weight of Pacific saury. The migration pattern was modified in 11 (33%) cases. In these cases, higher SST and size reduction under global warming prevented or delayed the southern migration of saury in winter. As a result, egg production was enhanced by the higher availability of prey plankton in the modified spawning region. A case study to separate the direct temperature effects was conducted, in which prey plankton density was assumed to be the same as the control run. The results suggest that an SST increase will directly reduce juvenile growth, whereas a prey plankton density decrease has an influence on the growth of adults and migration pattern, and hence egg production.