A survey was conducted in order to collect information for the stock status and various biological information on toothfish in Division 58.4.4a & b (Ob Lena Bank) by using a commercial bottom longline vessel, Shinsei Maru No. 3, from March 30 to May 2, 2011. The survey was undertaken according to the decision in the 29th CCAMLR Meeting of the Commission (CCAMLR-XXIX, 2010; paragraph 4.62). This report described the results during the survey in two SSRUs (B & C) of Ob Lena Bank. Total catch (excluding fish released alive) of Dissostichus eleginoides and other by-catch species was 37.8 tonnes in the survey area in 70 longline sets. D. eleginoides showed the highest catch of 35.4 tonnes, contributing 93.6 % to the total catch. CPUEs of D. eleginoides for 56 hauls where only trotline system was adopted in the SSRUs were 15.3 ± 1.1 indiv. / 1,000 hooks (mean ± SE) in terms of number and 111.2 ± 11.4 kg / 1,000 hooks in terms of weight. The CPUE in terms of weight in SSRU B (88.2 ± 13.5 kg / 1,000 hooks) was significantly lower than that (168.7 ± 22.2 kg / 1,000 hooks) in the same SSRU in the 2009/10 survey, although the CPUE in terms of number was same level between the years. This may be due to the catch of small fish in the shallow area < 500 m in the 2010/11. The smaller size of fish tended to be caught in the shallower area over the SSRUs. The operation was scarcely conducted in such shallow area and the average size of fish was larger in the 2009/10. The maturity index Stage I (immature) was dominant for both sexes of D. eleginoides during the 2010/11 survey. A total of 189 individuals of toothfish with good physical condition were tagged and released during the survey, and 4 D. eleginoides, which were tagged and released in SSRU C during the 2007/08 and 2009/10, were recaptured in the same SSRU. The overlap of size between the fish released with tag and that of overall catch was considerably high (θ=95 %).
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