Revised research plan for toothfish in Divisions 58.4.4 a and 58.4.4b by Shinsei maru No. 3 in 2012/13

A tagging survey in SSRUs B and C in Division 58.4.4 a & b was conducted in the 2011/12 fishing season with the aims of providing the data required for assessments of the population structure, size, movement and growth of Dissostichus spp. in the centred area of Division 58.4.4 a & b. An approximate stock biomass level of Dissostichus spp. in the survey area was tentatively estimated using Lincoln-Petersen and CPUE comparison methods. The medial estimate using Lincoln-Petersen (1 725 ton) was smaller than that 1 928 tonnes estimated in the WG-FSA meeting in 2011 (SC-CAMLR XXX, Annext 4, paragraphs 5.19-21).CVs of 20 % achievable from the biomass estimates may be achieved within three years with an annual research catch of approximately 50 tonnes. The estimate (976 tonnes) using CPUE comparison method was smaller than that using Lincoln- Petersen. We would continue the mark-recapture experiments in the 2012/13 season changing the targeted area from SSRUs B and C to SSRUs C and D due to avoid the huge loss of catch from killer whales in SSRU B. The catch biomass level in SSRUs B and C was calculated as 86 tonnes using Lincoln-Petersen and 54 tonnes using CPUE comparison at 5 % of exploitation rate. Because mean CPUE (67 kg /km) in SSRUs C and D was higher than that (62 kg /km) over the four year’s cruises (two year’s cruises for SSRU D), the proposed sample size as existing 70 tonnes for the next 2012/13 survey seems to be appropriate for the newly targeted area. To apply mark-and recapture studies, tagging rate of ≥ 5 fish / ton will be conducted. Only Trot line system will be used for all 71 hauls. However, if sufficient numbers of fish suitable for tagging are not captured using the normal trotline system, we would increase the comparison tests with trotline and Spanish line systems. We aimed the establishment of CASAL catch-at-age model for this Division by 2016/17.