The annual Random Stratified Trawl Survey was undertaken in Division 58.5.2 in the vicinity of Heard Island during May 2015. This paper provides a preliminary assessment of mackerel icefish population structure, abundance and yield for the area of Division 58.5.2 to the west of 79o 20’ E using standard CCAMLR methods. A large 2+ cohort is dominating the population. These projections indicate that catches of 482 t in the 2015/16 season and 357 t in the 2016/17 season.

The current season (2014/15) is the final one of the first three-season research which began in 2013 in data-poor fisheries. In the present report, the next three-season (2016-18) research plan in Subarea 48.6 was revised using the updated CCAMLR C2 and Observer data.

The stock sizes for five research blocks (48.6_1, 48.6_2, 48.6_3, 48.6_4 and 48.6_5) were estimated by the Petersen estimator and the CPUE x seabed analogy method. The stock size estimate using the Petersen estimator was relatively consistent with that using the CPUE method (using Division 88.2H as a reference area) for Dissostichus mawsoni in block 48.6_2. However, the estimates using the Petersen estimator were two-three times larger than those using the CPUE method in the block 48.6_3 and 48.6_4. Predicted numbers of tag recaptures from the estimated stock sizes using the both Petersen and CPUE methods (using Division 88.2H as a reference area) were relatively consistent with the observed numbers for D. mawsoni in the block 48.6_2 for 2012/13 and 2013/14 seasons. The predicted and observed numbers using either method were generally inconsistent for Dissostichus spp. in other blocks.

In the current season three Dissostichus mawsoni tagged and released in the previous seasons in the ice shelf block 48.6_4 were recaptured in the same block, which made it possible to estimate the stock size using the Petersen method for the block for the first time.

Understanding of the resource structure through clarification of their life history is essential to establish stock assessment and robust stock/ fisheries management of Dissostichus spp. population(s) in data- poor exploratory fisheries. During the second three-season research, we will continue enhanced tagging program, and collection and analysis of biological data including otoliths and gonads to clarify migration route and associated life stages of the fish.

To this end, we propose to follow the current research style in the current research blocks for the second three-season research with the sample sizes re-estimated following the procedure recommended at the WG-FSA in 2013 in order to maximize the expectation of tag-recapture to the extent possible under the precautionary exploitation rate. We expect further progress of tagging research in the southern research blocks during the next three-season research because several fish tagged and released in the preceding seasons began to be recaptured.

In addition we propose the westward extension of the research block 48.6_4. The expanding the boundaries of the research block may promote sufficient utilization of the catch limit, which enables us to make more reliable stock estimation, and also be more likely to detect tagged fish that had moved off research block to the continual slope/shelf.