A survey was conducted in order to collect information for the stock status and biology of toothfish in the Division 58.4.3b (BANZARE Bank), using a commercial bottom longline vessel Shinsei Maru No. 3, from 24th May to 5th June, 2012. Due to unexpected bad weather and sea condition, the vessel and some equipments on board were frozen, the operations were delayed and the fuel oil for the stability of the vessel was wasted. Unexpected low fish catches in the preceding survey in Ob-Lena Bank during the same cruise and the wasteful use of baits also lead to the decline of the stability of the vessel. The above mentioned situation forced the vessel to interrupt the survey halfway to ensure the safety of voyage. Shinsei Maru Trot line system with modified configurations was used as fishing gear for 16 hauls. Mean CPUE of Dissostichus spp. was 52.2 kg / km (CV = 107 %). This was identical with the mean CPUE of 51.8 kg / km in the 2010/11 survey. Total of 51 individuals of toothfish with good physical condition and single-hooked were tagged and released during the survey. No toothfish was recaptured. Fish with good physical condition and single-hooked contributed 26-39 % to the total fish caught by the two kinds of modified trotline configurations recommended by WG-FSA in 2011.
We propose to continue the survey focusing mark-recapture experiment in the 2012/13 season with slightly modified spatial designs. An approximate stock biomass level of Dissostichus spp. in the target stock area was estimated to be 8 444 tonnes, using CPUE comparison method. This was lower than the estimate of 13 592 tonnes using the mean CPUE from 2007/08 to 2009/10. However, the survey area in 2011/12 overlapped well with that in the 2010/11 and the CPUE was identical between the two years nevertheless the numbers of hooks for the trotline configuration for the 2011/12 survey were reduced to 60 % of normal configuration. Thus the existing catch limit of 40 tonnes seems to be appropriate for the 2012/13 survey. We would examine the appropriate scheme to complete the survey in 2012/13 such as changing the survey season, separating the cruise between the surveys in Ob-Lena Bank and BANZARE Bank for securing enough ship-time, etc.