Evaluating the spatiotemporal dynamics of Pacific saury in the Northwestern Pacific Ocean by using a geostatistical modelling approach

Abstract

Pacific saury (Cololabis saira) is an important fisheries resource and an ecologically important fish in the Northwestern Pacific Ocean. Some evidence indicates that its distribution is affected by the environmental variability, but the relative importance of environmental effects versus those of other unmodelled spatiotemporal processes has not been investigated. For this reason, fisheries data from members of the North Pacific Fisheries Commission, were analyzed using a geostatistical modelling approach to examine interannual variation in the spatiotemporal distribution of Pacific saury in the Northwestern Pacific Ocean during the fishing season (May–December) from 2001–2017. The objectives were to investigate the extent to which this can be attributed to changes in the local (e.g., sea surface temperatures), regional environmental variables (e.g., Southern Oscillation Index), and the unmodelled spatiotemporal variables (e.g., species interaction). We found that the centroid of gravity of Pacific saury had an apparent eastward shifting after 2013, and a further shift with a lower relative abundance in 2017. We also found that neither a single local or regional environmental variable nor any combination of them could explain the distributional shift of Pacific saury. Instead, the change in spatial distribution is mostly attributed to the “unmodelled” spatiotemporal variables. We emphasize that developing a quantitative understanding of the underlying mechanisms is a critical area for future work. In the future, environmental data is expected to become increasingly available. However, we caution that before projecting the Pacific saury distribution resulting from climate change or other environmental phenomena, analysts should first determine whether the hypothesized driving variables account for a meaningful proportion of variability in the historical distribution data.