Revised reports on abundance and biological information on toothfish in Divisions 58.4.4 a and 58.4.4b by Shinsei maru No. 3 in 2011/12

A survey was conducted in order to collect information for the stock status and various biological information on toothfish in SSRU B and C of Division 58.4.4a & b (Ob Lena Banks) from April 15 to May 19, 2012. Total catch (excluding tagged and released fish) of Dissostichus eleginoides was 28.3 tonnes in the survey area in 70 longline sets. Mean CPUEs of D. eleginoides was 48.3 kg / km (CV = 79.1%) in terms of weight. The mean CPUE in terms of weight in SSRU B (32.1 kg / km) was rather lower than that (50.5 kg / km) in the same SSRU in 2010/11. A total of 172 individuals of toothfish with good physical condition and single-hooked were tagged and released during the survey, and 3 D. eleginoides, which were tagged and released in SSRUs B and C from the 2007/08 to 2010/11, were recaptured in the same SSRUs, respectively. Fish with good physical condition and single-hooked contributed 50 % to the total among fish caught by Spanish line system, while this kind of fish contributed 14 % to the total among fish caught by trotline system. A total of 133 killer whales（Orcinus orca）were observed at the 30 hauls. All of whales occurred in SSRU B. The vessel tried to avoid killer whales as in the previous surveys but could not escape from them effectively in SSRU B. Seventy-nine % of sets to the total were affected by killer whales in SSRU B in 2010/11 and 2011/12. On the other hand, no set was affected by killer whales in SSRU D in 2007/08 and 2009/10. Generalized additive model analysis indicated that the presence of killer whales leads to huge loss (ca. 40 %) of catch of D. eleginoides in SSRUs B and C.