Research-based New and Exploited fisheries have been conducted in order to collect information for the stock status and biology of toothfish in the Division 58.4.3b (Banzare Bank), using a Japanese commercial longline vessel Shinsei maru No. 3, during 2006/07 and 2011/12. Total number of hauls ranged from 22 to 148 during the six cruises. Total catch of Dissostichus spp. ranged from 9 to 108 ton. Predicted CPUE (catch/km) for D. eleginoides and D. mawsoni varied with years but showed no upward and downward tendencies with years. D. mawsoni mainly occurred in the shallower areas > 1 200 m but decreased in the CPUE as the depth decreased, while D. eleginoides mainly occurred in 600 – 1 000 m depths but rarely occurred in the deeper areas > 1 400 m. Progressed stages of GMI and high GSIs for D. mawsoni were observed in 2010/11 and 2011/12 when the researches were conducted in May and June, suggesting that Banzare Bank is one of important spawning grounds for D. mawsoni. On the other hand, such an apparent seasonal development of the maturity indices was not observed for D. eleginoides. Predicted trot line CPUE was significantly higher than Spanish line for D. eleginides, but no significant difference in the CPUE between gears was observed for D. mawsoni.
We would continue the survey focusing mark-recapture experiment in the 2012/13 season with a little modified spatial design. An approximate stock biomass level of Dissostichus spp. in the target stock area was estimated to be 8 444 tonnes, using CPUE comparison method. Applying a precautionary discount factor for biomass estimated of 0.3 and a precautionary exploitation rate of 0.01, catch biomass level was calculated as 84.4 ton. Thus the existing catch limit of 40 tonnes seems to be appropriate for the 2012/13 survey. We aimed the establishment of CASAL catch-at-age model for this Division by 2016/17.