Climate change and interspecific interactions drive species alternations between anchovy and sardine in the western North Pacific: Detection of causality by convergent cross mapping

The abundance and recruitment of anchovy Engraulis spp. and sardine Sardinops spp. alternate in a synchronized way across the Pacific. Convergent cross mapping (CCM) indicated that climate change drives the alternation of the two species in the California Current System. However, climate indices patterns in the western North Pacific contrast with those in the eastern North Pacific, despite synchronous species alternations occurring. Therefore, it is of great interest to clarify whether climate change, or any other factors, affects the population dynamics of Japanese anchovy and Japanese sardine in the western North Pacific. Using CCM, we tested whether climate change and interspecific interactions affect the population dynamics of these two species. We found that climate change affected recruitment, and we clarified the spatiotemporal pattern of this effect. This result supports the existing hypotheses that population dynamics are regulated by climate change in the western North Pacific. The present study also detected interspecific interactions between sardine and anchovy, which might promote the alternation of the two species, and has not been reported in other regions.