Modelling the spatio-temporal dynamics of Pacific saury in the Northwestern Pacific Ocean by using a Vector-Autoregressive Spatio-Temporal Model

We quantified the spatiotemporal dynamics of the Pacific saury (Cololabis saira) in the Northwestern Pacific Ocean between 2001 and 2017 by using the Vector-Autoregressive Spatio-Temporal Model. Results indicated that the high density area of the Pacific saury was located in the coastal and offshore waters off Japan (35-45 °N and 140-155 °E) during the studied period. There is evidence that the spatial distribution of the Pacific saury has gradually shifted eastward over time. We investigated whether the Pacific saury has shifted which can be attributed to changes in a single environmental variable or climatic index, the multiple environmental variables and climatic indices, and the unexplained spatio-temoporal factors. Results indicated neither a single environmental variable or climatic index nor the linear combination of them could explain the spatial distribution shift of the Pacific saury. Instead, the change in spatial distribution is the most strongly attributed to the ‘unexplained’ factors. We suggest that any studies regarding the likely impacts of future environmental changes on the Pacific saury should first quantify the proportion of historical variation that can be explained by the variables that are available for forecasting.