The behaviour patterns of Japanese krill fishery vessels in Area 48 were analysed using questionnaires on the reasons why the vessel changed their fishing grounds, which were sent out to of the Japanese fishing vessel since the 1989/90 fishing season. Among many reasons for changing fishing grounds, krill density, krill, size, ice condition, transshipment, and salp-by catch accounted for 95.6% of the changes. Although low krill density was the primary reason for changing fishing grounds, other seasonal factors such as greenness or ice condition could become important. A general picture of the seasonal succession of the Japanese krill fishing operation revealed that they tend to utilize fishing grounds close towards the southern limit within the ice free range. This pattern may well vary between nations, and it is essential to perform similar analyses for the other nation’s vessels. A conceptual model for Japanese krill fishing operation is proposed.