An exploratory spatial data analysis-based investigation of the hot spots and variability of Ommastrephes bartramii fishery resources in the northwestern Pacific Ocean
The oceanic cephalopod Ommastrephes bartramii is widely distributed in the northwestern Pacific Ocean and is an important target species for the fishing industries of Japan, South Korea, China and Chinese Taiwan. Owing to the effects of global climate change and increased fishing activities, the spatial patterns and hot spot dynamics of O. bartramii resources are changing. This study focused on O. bartramii resources, especially within the boundaries of 150°E-160°E and 38°N- 45°N, in the northwestern Pacific Ocean. Based on original fishing data from Chinese boats, the study aimed to explore the spatial structure of O. bartramii resources using integrated methods of spatial statistics, global spatial autocorrelation, change detection and landscape metrics. Classical statistics and global spatial autocorrelation-based primary analysis showed that there were vast differences in the resource abundance of O. bartramii over the study area. A relatively strong aggregated distribution was observed for O. bartramii in the northwestern Pacific Ocean. In addition, spatial hot and cold spot maps were produced for the years of 2007 and 2010 using both a geographic information system and local spatial autocorrelation methods. The maps illustrated that there were three obvious hot spots and one cold spot for O. bartramii in the northwestern Pacific Ocean in 2007, whereas in 2010 there was one obvious hot spot and four cold spots. Change detection demonstrated that only one spatial hot spot remained unchanged between 2007 and 2010, while two areas showed a change in status from hot to cold spots. In addition, only one of the cold spots remained unchanged between 2007 and 2010. As a result, the non- hot and non-cold spots that showed non-aggregated or random distributions dominated the pattern of O. bartramii in the northwestern Pacific Ocean. Landscape metrics were also employed in this study to mine the implicit information and knowledge of hot/cold spots of O. bartramii resources. This research demonstrated that relatively low complexity and self- similarity were observed for the O. bartramii resource, while strong spatial heterogeneity and aggregation, as well as high integrity and cohesion, were detected for the same fishery resource. Finally, a sea surface temperature-based analysis revealed the marine environmental characteristics and dynamics of spatial hot/cold spots of O. bartramii in the northwestern Pacific Ocean in both 2007 and 2010. The results showed that, owing to the influence of sea surface temperature and currents within the fishing area of the northwestern Pacific Ocean, approximately half of the area has relatively high production. However, high production alone cannot account for the hot spot clustering within most of the study area. Hence, in 2007, only 7.0% of the study area was classified as hot spots, while most of the area comprised cold spots or areas that were not statistically significant. As a result of the Oyashio Current, the fishing grounds distributed at 40°-45°N and 154°-158°E during the best fishing period displayed relatively aggregated spatial hot spots in 2010, whereas the spatial cold spots were scattered across the northwestern Pacific Ocean.