Fishing patterns of Japanese krill trawlers

Log book data from Japanese Krill Trawlers were used to characterize their fishing strategies, especially focusing on their movement in time and space. The operations were grouped into ‘operation units’ which consists from a group of repeated operations within certain searching ranges (10nm, 30nm, and 60nm). Distribution of the operation units showed considerable variation in space and time.
CPUE based on 10 x 10 squares were also examined. CPUE by shots and towing time did not show good match with the plots of aggregated catch, suggesting these two kinds of CPUEs may not be good indices for expressing the status of krill in the fishing ground. Catch per fishing days maybe the reasonable index for expressing the status of krill in the fishing ground.