Species‐Specific Temporal Shifts in Distribution Patterns of Japanese Sardine and Japanese Anchovy in the Western North Pacific in Relation to the Pacific Decadal Oscillation

ABSTRACT The biomass of Japanese sardine and Japanese anchovy is generally considered to cyclically fluctuate in response to climate‐related oceanic changes such as Pacific decadal oscillation (PDO). However, little is known about how their spatial ecology changes in relation to the periodic oceanic changes. In particular, the spatial distributions and responses to changes in water temperature of both species, along with shifts in PDO and abundance, are unclear. To reveal the spatiotemporal dynamics in relation to biomass fluctuation and PDO, we estimated the densities, the spatial distributions and thermal niche of both species in the western North Pacific during autumn from 2005 to 2020, using spatiotemporal models. The results indicated that the sardine abundance increased, whereas their distribution pattern was relatively stable during the study period. In addition, their estimated thermal niche (the estimated temperatures associated with their distributions using spatiotemporal models) did not change across PDO phases. In contrast, Japanese anchovy exhibited a notable shift in its distribution pattern from offshore to coastal regions of the Japanese archipelago and a change in their thermal niche over the study period. The present study suggests that temporal variability in the thermal niche is key to explaining species‐specific differences in distribution shifts under environmental change. This insight will help improve the projection accuracy of distribution shifts and enhance assessments of climate change impacts on population dynamics of fish species.