Seasonal and Multidecadal Changes in the Distribution of Small Cetaceans Inhabiting the Western North Pacific Under a Changing Ocean Environment, Inferred From Species Distribution Models

ABSTRACT Aim For several decades, substantial efforts have monitored cetacean distribution and abundance in the western North Pacific. Large‐scale visual‐based line transect surveys have been conducted since the early 1980s, covering almost the entire western North Pacific. However, information on distribution patterns of cetacean species is concentrated in summer months when sighting conditions are preferred, while dolphin fisheries, one of the main threats to cetacean populations, are conducted mainly during winter months. Location The western North Pacific. Methods To fill information gaps between these seasons and improve conservation and management measures, we compiled long‐term sighting data. We constructed a simple species distribution model (SDM) to estimate the seasonal patterns for 14 delphinid and phocoenid species. Although the sighting data remained limited outside summer, the distribution probability was intra‐ and extrapolated to respective seasons using the constructed SDMs. Results Model fitting tended to be better for the species inhabiting higher latitudes than for those in lower latitudes. In addition, seasonal patterns observed in our habitat prediction maps roughly corresponded to those patterns previously reported from coastal fishers' logbooks and satellite‐tracking records. The model also estimated that some species distribution changes in response to long‐term warming in water temperature over the past 30 years. Main Conclusions The study addresses the seasonal gaps in conservation and management measures and improves understanding of population structures of the species targeted by dolphin fisheries. Our approach to predicting distribution patterns spatiotemporally is widely applicable to conservation systems for marine animals inhabiting dynamic ocean environments.