| Summary: | Japanese sardines (<i>Sardinops melanostictus</i>) are environmentally sensitive pelagic fish. We investigated the effects of environmental factors on the stock-recruitment (S-R) relationship of <i>S. melanostictus</i> in the Pacific Ocean from 1984 to 2018. We modeled and analyzed the recruitment of <i>S. melanostictus</i> using the Ricker model, the Ricker environment extension model (Ricker-E), and the generalized additive model (GAM). Different numbers of environmental factors were added to the models for fitting, and the Akaike information criterion (<i>AIC</i>) was used to select the optimal model. The results showed that the nonlinear GAM provided the best fit. The results of the GAM single factor and multifactor analysis showed that environmental factors were significantly correlated with recruitment in <i>S. melanostictus</i> (<i>p</i> < 0.05). The best fitting model was the GAM, with an <i>AIC</i> of 57.9 and a cumulative explanation rate of 95.7%. Sea surface temperature was the most dominant environmental factor and had a negative impact on R/S. Considering both spawning stock biomass (S) and the environmental factors in the S-R relationship is important for studying the mechanisms of complementary changes and population changes in <i>S. melanostictus</i> under the influence of the marine environment.
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