Effects of Kuroshio Current Variability and Pacific Decadal Oscillation on Recent Decline in Chub Mackerel (Scomber japonicus) Catch in the Northwestern Pacific in the 2020s

Chub mackerel (Scomber japonicus), a key commercial species in the Northwestern Pacific, has experienced notable declines in catch since 2019, prompting an investigation into the environmental factors affecting its catch and abundance. This study explores the connections between Chub mackerel catch variability and ocean environmental changes, including upper-ocean temperature, sea level anomaly, net primary production, and influences from large-scale climate phenomena such as the Pacific Decadal Oscillation (PDO) and variations in the Kuroshio Current. Results indicate that variations in the path of the Kuroshio Current around southern Japan and its extension significantly correlate with Chub mackerel catch fluctuations, rather than upper-ocean temperature variability in the feeding and nursery grounds along the east coast of Japan. Additionally, the results underscore the influence of PDO-driven ocean processes on Kuroshio Meandering and its extension, which may establish biologically adverse conditions affecting spawning success and consequently, catch and abundance. These results provide insight into the recent declining trend of chub mackerel catches associated with the PDO-related Kuroshio Meander and its extension variability, provide a basis for estimating catch variability using the relationship between catch and climate variability, and contribute to the development of adaptive management and conservation strategies.