Revised research plan for toothfish in Division 58.4.4 a and b by Shinsei Maru No. 3 in 2011/12

A tagging survey in SSRUs B and C in Division 58.4.4 a & b was initiated in the 2010/11 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 (SSRUs B and C in Division 58.4.4 a & b) was estimated using simple Petersen, CPUE x area, and CPUE comparison methods. The medial estimates using simple Petersen (1583 and 2751 ton) were similar to those under the two scenarios analyzed at WG-FSA in 2010 (1580 and 3036 ton), although the 95 % confidence intervals were wide due to small numbers of recapture. The estimations using other two methods were a half to a quarter smaller than those using simple Petersen. The medial stock biomass estimated under the two scenarios at WG-FSA in 2010, which allowed determining the sample size as 53 tonnes for the 2010/11 survey, are identical with those estimated using the simple Petersen. Therefore we think that the result using the simple Petersen is more plausible and proposed sample size as 53 tonnes for the next 2011/12 survey is appropriate. We propose to continue the mark-recapture experiment in SSRUs B and C in the 2011/12 season, with nearly same survey design as in the 2010/11. A total of 71 research hauls will be allocated in the same locations on 7.5-minute latitude x 15-minute longitude grid points except one haul which are newly allocated in the northeast of SSRU B instead of an unconducted haul in the 2010/11. To apply mark-and recapture studies, tagging rate of 5 fish / ton will be conducted. The comparison test with the experimental gear, which consists of three segments of Trot line system and Spanish line system respectively, will be conducted at 14 hauls, due to understanding of differences in the physical conditions of tagged fish between those caught on Spanish lines and those caught on trotlines.