Spatial variability of fishing grounds in response to oceanic front changes detected by multiple satellite measurements in the East (Japan) sea

In the East (Japan) Sea, the ocean fronts resulting from coastal upwelling and eddies affect the formation of fishing grounds by creating an environment with abundant food resources. The aim of this study was to examine the relationship between fishing activities and the locations of these ocean fronts. To do this, Day/Night Band (DNB) images were used, and ocean fronts were detected based on satellite ocean colour data. It was found that the illuminated pixels on the DNB images were related to the number of sailed out boats (coefficient of determination, R-2 = 0.55) and so may represent the number of fishing activities. Consequently, a new index was developed to assess the spatial correlation between the locations of fishing activities and ocean fronts, referred to as the 'DNB score,' which combined the scientific method of determining the locations of regional ocean fronts with the social method of observing the locations of fishing activities based on fishermen's experiences. The DNB score was approximately 21% for the coastal upwelling front and 44% for the eddy front. Since most boats with lights in the East Sea are known to be fishing for Todarodes pacificus, the relationship between the DNB score and the catch of T. pacificus was also examined. This showed that the DNB score reflected the temporal catch variability and the catch per unit effort of T. pacificus, suggesting that it could be used as an index to evaluate the location of fishing grounds in association with fishing activities.