Multi-decadal distribution changes of commercially important demersal species in the central-western Sea of Japan based on a multi-species spatiotemporal model

Understanding long-term changes in the distribution of commercially important species is a key first step for developing appropriate management plans. We estimated multi-decadal changes in the distributions of seven demersal fish species in the central-western Sea of Japan by fitting a multi-species spatiotemporal model to catch and effort data from a Japanese offshore trawl fishery from 1982 to 2020. We then identified any spatiotemporal patterns and discussed their relationship to oceanographic factors. Large distribution expansions were detected for Pacific cod (Gadus macrocephalus) and blackthroat seaperch (Doederleinia berycoides) in the southwestern region of the study area in the 2000s and 2010s. Combined with previous findings and an interannual trend of water temperature, it is thought that these changes could have been caused by expansions in the distribution of optimal thermal condition for stock-recruitment relationships. Species that did not experience large changes in distribution, such as cold-water flounders [the flathead flounder (Hippoglossoides dubius) and Korean flounder (Glyptocephalus stelleri)], mainly inhabit deep waters that are thought to be dominated by a colder and homogeneous water mass, meaning that their habitats were more likely to remain stable over time. Our results will contribute to improvement of adaptive stock managements for commercially important demersal species.