Use of nighttime visible images to detect Japanese common squid Todarodes pacificus fishing areas and potential migration routes in the Sea of Japan

Abstract

This study used Defense Meteorological Satellite Program (DMSP)/Operational Line- scan System (OLS) satellite images to classify and analyze the spatial and temporal variability of nighttime fishing vessel lights in the Sea of Japan. OLS images can detect the powerful lights used to attract squid. We examined DMSP/OLS nighttime visible images from 1994 to 1999. Fishing areas of the Japanese common squid Todarodes pacificus were defined as the bright areas created by 2-level slicing methods on DMSP/OLS images. T. pacificus fishing areas were mainly found along the east coast of Korea, between Cheju and Tsushima Islands, around the Yamato Rise, along the coast of Honshu, and in northern areas of the Sea of Japan. Using image classification and separability analy- sis, we divided the Sea of Japan into 7 areas based on different temporal variability in squid fishing area characteristics. The classification takes the potential northern and southern squid migration pat- terns into account. One of the potential northern migration patterns formed along Honshu Island to the north; another appeared along the east coast of Korea, northward through Yamato Rise. Southern migration patterns were almost the reverse of northern migration patterns. These 7 classified areas also correspond to the oceanographic characteristics of the Sea of Japan, i.e. a polar front at latitude 40°N, the inflow of the Tsushima Warm Current (TWC), and warm eddies. The use of remotely- sensed data demonstrated in this study offers a powerful and innovative way in which to determine the migration and ecology of the Japanese common squid.