Japanese krill fishing operations were observed on board a commercial vessel and the actual operation described in detail. ‘Fish-finder’ was most useful in detecting swarms, while sonar was used to judge the towing direction. The size of fished swarms ranged from 100 m to 10 km with different distributions occurring in different fishing areas. While catch per towing time reflects within-swarm density, catch per day was thought to be a good index to measure abundance of a concentration. Comparison of such an index across time and space may prove difficult due to problems of standardization when data from different vessels are to be used.