Here we propose the northeastward of research block of 48.6_2 along ridges to promote sufficient utilization of the catch limit, which enable us to complete planned research, evaluate the habitat model and elucidate stock structure. The distribution of densities (catch per haul in 20-minute grid) of Dissostichus mawsoni is shown in Figure 1. The research operation for the block 48.6_2 has been concentrated in its southeastern bank (south of ca. 55.2°S) with higher fish densities but scarce in the northern area with lower fish densities, and it has not taken approximately 50-70% of the annual catch limit (CL=170 tonnes) since the current research block was set in 2013. Thus, unutilized portions of catch limit were mainly attributed to low CPUE in the northern part of the block.
Meanwhile, the habitat model (WG-15/64, 2015) predicts the existence of dense population of D. mawsoni in area northeast of the research block 48.6_2 along the extended ridges. Moreover, the fishes tagged and released tended to move along the ridges running southwest and northeast in the block, which suggests the exchange of population between the research block and the northeastern area (Fig. 2).
Therefore, we propose the extension of this research block to its northeastward along ridges (Fig.2) under the current catch limits to promote completion of planned research and examination of the habitat model and the stock structure.