Long-term variability analysis of the habitat suitability index for Todarodes pacificus (Japanese common squid) using MODIS-Aqua dataset in the East/Japan Sea, South Korea.

The marine fishery resources in South Korea, including Todarodes pacificus (Japanese Common Squid), have experienced significant changes, prompting concern and investigation. This study aimed to develop a habitat suitability index (HSI) model for T. pacificus around South Korea using remote sensing datasets and to analyze its long-term variability. The HSI model was constructed based on the fishing efforts, offering a more accurate representation of habitat distribution for this short-lived species. Key environmental variables-sea surface temperature (SST), sea surface height anomaly (SSHA), chlorophyll-a (Chl-a), and primary productivity (PP)-were identified as critical for the habitat distribution of T. pacificus. The preferred environmental conditions for T. pacificus were found to be 14.64-27.81 °C for SST, 0.32-1.28 mg m for Chl-a, -0.04 to 0.2 m for SSHA, and 346-616 mg C m d for PP. Seasonal HSI models empirically derived demonstrating a strong positive correlation with fishery landings (r = 0.8921). Long-term analysis from 2002 to 2020, using Empirical Mode Decomposition (EEMD), revealed a significant decline in HSI in the East/Japan Sea, which corresponded with a decrease in the annual catch of T. pacificus. This decline in HSI and fishery production is likely influenced by long-term environmental changes, such as ocean warming and declining PP, which may alter habitat conditions and resource availability. These findings highlight the importance of sustained ecosystem monitoring and adaptive management strategies for the conservation of T. pacificus. Further studies focusing on the detailed interactions between climate change-induced environmental changes and the physiological and phenological responses of T. pacificus are crucial to fully understand and address its ongoing population shifts.