Revised research plan for toothfish in Divisions 58.4.4a and 58.4.4b by the Shinsei Maru No. 3 in 2010/11

In order to clarify the stock status and biological characteristics of Dissostichus spp. In Division 58.4.4 a & b, we proposed the research plan for toothfish in the Division by Shinsei Maru No. 3 to be conducted throughout the whole four SSRUs (A-D) in the Division in April-June 2011 in the WG-SAM 2010 meeting. However, during the first survey in 2009/10, when the research was surveyed throughout the whole SSRUS, evenly spaced 10 nautical miles apart, only one tagged fish was recaptured. Then, following advice taken in WG-SAM 2010 meeting that research should concentrate effort on a subset of the management area where the probability of recapture is low (WG-SAM 2010 report paragraph 3.21), we revised the research plan to be concentrated in the two centered SSRUs, B and C. These centered SSRUs were selected due to increasing possibility of recapture for tagged fishes released throughout the four SSRUs in 2007/08 and 2009/10. Mean CPUE in weight in the 2009/10 season was significantly higher than that in the 2007/08 season (p = 0.02). The research hauls are revised to be allocated on more concentrated 7.5-minute latitude x 15-minute longitude grid points, taking into account the increase of the recaptures. A Trot line system will be employed for all hauls. To apply the mark-and-recapture studies, sufficient tagging rate of 5 fish/ton will be conducted. We calculated 77 tonnes of total allowable sample size for the 2010/11 survey, taking into account the need for completion of the survey and impact on the fish stock. However, this calculation contains several implicit assumptions as pointed out in WG-SAM 2010 (WG-SAM 2010 report paragraph 3.24). Thus we will take advices for the appropriate methods of estimations to overcome these problems in the WG-FSA-2010 meeting.