Revised reports on abundance and biological information of toothfish in Division 58.4.3b by Shinsei Maru No.3 in 2010/11 and proposal of the consecutive survey in 2011/12

A survey was conducted in order to collect information for the stock status and biology of toothfish in the southeast sector (24 allocated hauls) of Division 58.4.3b (BANZARE Bank), using a commercial bottom longline vessel Shinsei Maru No. 3, from May 7 to 16, 2011. Shinsei Maru Trot line system was used as fishing gear for 19 hauls. Comparison test using trotline and Spanish line systems were made for 5 hauls. Total catch (excluding fish released alive) of Dissostichus spp. and other bycatch species was 12.0 ton in the SE sector, where the catch limit of 15 ton was set. Mean CPUE of Dissostichus spp. was 58.8 kg / km (CV = 66.7%; 105.9 kg / 1,000 hooks) for the hauls where only trotline system was employed. This was lower than 69.6 kg / km (CV = 51.3%; 125.0 kg / 1,000 hooks) in the 2009/10 survey, although there was no significant difference. Total of 62 individuals of toothfish with good physical condition were tagged and released during the survey. No toothfish was recaptured. The overlap of size between the fish released with tag and that of overall catch was considerably high (85 % for D. mawsoni and 79 % for D. eleginoides). There was a significant difference in physical conditions of D. eleginoides between Spanish line and trotline (χ2 test, P < 0.05), with the higher percentage of bad condition (54.6 %) for trotline. It seems that smaller fish < 80 cm are more damaged than larger ones for trotline system in D. eleginoides.

An approximate stock biomass level of Dissostichus spp. in the survey area was estimated to be 174-175 ton, using CPUE x area and CPUE comparison methods. From this, the appropriate sample size in the next year survey was calculated to be 5.2 ton based on the criterion for the depleted stock shown in WG-FSA-10/42. However, the estimated biomasses using the two methods seem to be a quarter – a half underestimated compared to those using GYM at WG-FSA in 2010 in case of Ob-Lena Bank, and therefore we think that the total allowable size of 15 ton (ca. 3 times of 5.2 ton), along with the same survey designs as in the 2010/11, is appropriate for the next survey.