CCAMLR

The current season (2015/16) is the first one of the second three-season research in data-poor fisheries. In the present report, the next season research plan in Division 58.4.1 was made using the updated CCAMLR C2 and Observer data.

The stock sizes for five research blocks (58.4.1_1, 58.4.1_2, 58.4.1_3, 58.4.1_4 and 58.4.1_5) were estimated by the Petersen estimator and the CPUE x seabed analogy method.

Understanding of the resource structure through clarification of their life history is essential to establish stock assessment and robust stock/ fisheries management of Dissostichus spp. population(s) in data- poor exploratory fisheries. During the second three-season research, we will continue enhanced tagging program, and collection and analysis of biological data including otoliths and gonads to clarify migration route and associated life stages of the fish.

To this end, we propose to follow the current research style in the current research blocks for the next season research with the sample sizes estimated following the procedure recommended at the WG-FSA in 2013 in order to maximize the expectation of tag-recapture to the extent possible under the precautionary exploitation rate.

The subarea 88.3 is a large area contained from 105° W to 70° W where has been closed to directed fishing following the results of a Chilean survey activities in 1998 (SC-CCAMLR-XVII/BG/7). Previous three research surveys conducted by the New Zealand and the Russian flagged vessels since 1998. It was noted that 8 D. Mawsoni were tagged by the New Zealand in the 2004/05 season and 123 D. Mawsoni were tagged by Russian flagged vessels in the 2010/11 and 2011/12 season (WG-FSA-05/53, WG-FSA-11/36 & WG-FSA-12/13). It was also noted that no tagged fishes were recaptured during the previous research activities. Considering this large region, the Republic of Korea notes that only 95 research hauls and 131 tagged fishes from three research activities (in total since 1998) were not enough likely to recapture. it was further noted that there was no research activities more than two consecutive years in the past despite the Scientific Committee has agreed that research fishing should be conducted such that it results in an assessment of a stock in 3-4 years time (SC-CAMLR XXVIII, paragraphs 4.165). During the 2015/16 season the Korean flagged vessel, Greenstar, conducted 1^st year research in this area. Total of 566 D. Mawsoni were tagged and released. Although the Greenstar set 108 research hauls in the Subarea 88.3 she did not find any recaptures of previous surveys. In second research year, the Greenstar is planning to revisit to the areas where the tagged fishes were released to further understand toothfish movement and migration with recapture data.

Most things related to Dissostichus spp. in the eastern side of Antarctic Ocean has not been known well as namely the area is data poor areas. In the Division 58.4.1 there are two stocks; one extends from the SSRU 58.4.1C to the SSRU 58.4.2A, and the other one to the SSRU 58.4.1H. The population sizes were vulnerable with a big range of about 1,000-2,000 t per SSRU in 58.4.1. During the 2004-2015 fishing seasons in Division 58.4.1, 6,813 Dissostichus spp. were tagged and released, but only 28 fishes among them have been recaptured which were not enough data to estimate stock biomass for considering the precautionary catch limit. Therefore, the catch limits that the meeting got in 2013 meetings increased to get more recapture. The food-web of Dissostichus spp. has started to be studied in the southern Ross Sea and 58.4.1C. Some studies on biology of the fish have been evaluated, but those are not enough to assess the stocks and consider proper management measures. Based on CCAMLR’s fishery report, the eastern area is still data-poor area showing low recapture rate. Consequently, providing catch and effort data from the area, analysing biological samples, and collecting recapture data focusing on SSRUs in Division 58.4.1is very important.

Korean research plans were endorsed by the Scientific Committee at SC-CAMLR-XXXIII. The Korean scientists collected and analysed the catch, effort, and biological data such as length, weight, gonadal development, and muscle by Kingstar in Divisions 58.4.1 and 58.4.2 in 2014/15-2015/16 season. Korea will also conduct the exploratory fishery with research plan for Dissostichus spp. in the SSRUs in Divisions 58.4.1 and 58.4.2 in 2016/17 using Korean commercial bottom longline vessel, Kingstar belonged to Sunwoo Company in accordance with paragraph of CM 24-01 and paragraph 6 (iii) of CM 21-02 to collect the catch and effort, CTD, tagged and released, recaptured data including archival tag, biological data for estimating biomass for Dissostichus spp. using CASAL and evaluating migration and distribution pattern by developmental maturity and size stages.

Here we propose the northeastward of research block of 48.6_2 along ridges to promote sufficient utilization of the catch limit, which enable us to complete planned research, evaluate the habitat model and elucidate stock structure. The distribution of densities (catch per haul in 20-minute grid) of Dissostichus mawsoni is shown in Figure 1. The research operation for the block 48.6_2 has been concentrated in its southeastern bank (south of ca. 55.2°S) with higher fish densities but scarce in the northern area with lower fish densities, and it has not taken approximately 50-70% of the annual catch limit (CL=170 tonnes) since the current research block was set in 2013. Thus, unutilized portions of catch limit were mainly attributed to low CPUE in the northern part of the block.

Meanwhile, the habitat model (WG-15/64, 2015) predicts the existence of dense population of D. mawsoni in area northeast of the research block 48.6_2 along the extended ridges. Moreover, the fishes tagged and released tended to move along the ridges running southwest and northeast in the block, which suggests the exchange of population between the research block and the northeastern area (Fig. 2).

Therefore, we propose the extension of this research block to its northeastward along ridges (Fig.2) under the current catch limits to promote completion of planned research and examination of the habitat model and the stock structure.

South Africa and Japan made the next season’s (2016/17) research plan in Subarea 48.6 using the updated CCAMLR C2 and Observer data.

We have firstly checked data quality and found some abnormal data for the two vessels in block 48.6_2, therefore we removed the data for the current analysis.

We investigated the biological features of D. mawsoni using Observer data. The geographical distribution of sizes, GSI and Fulton’s condition factors for D. mawsoni in Subarea 48.6 suggest that northward spawning migration and southward feeding migration as Ross Sea stock. Life history seems to be related to the Weddell gyre system from the location, but the larvae dispersion model previously reported shows that larvae are driven further eastward. We cannot identify an appropriate stock unit currently.

The stock sizes for five research blocks were estimated using the Chapman estimator, the CPUE analogy method and preliminary CASAL models. We divided the two areas for block 48.6_2 by latitude of 55.2°S to estimate the biomasses of D. mawsoni because the recaptures were concentrated in the southern area. In addition, we considered that only recaptures for 1 year at liberty is effective to estimate the precautionary biomass for D. mawsoni in block 48.6_2 and 48.6_3 because of recaptures with short period at liberty.

Predicted numbers of tag recaptures from the estimated stock sizes using Chapman were relatively consistent with the observed numbers for D. mawsoni in the southern area of block 48.6_2, and blocks 48.6_3 and 48.6_4. The predicted numbers were generally inconsistent for Dissostichus spp. in other blocks.

We estimated predicted numbers of recaptures in the next three years using present catch limit and precautionary exploit rate of 4 % based on Chapman estimator and CPUE analogy method.

Japan proposes the northeastward extension of the current research block 48.6_2 in order to elucidate the stock structure. Details are described in a separated document (Namba et al., WG-SAM-16xx, 2016).

Japan and France made the next season’s (2016/17) research plan in research blocks 58.4.4b_1 and 58.4.4b_2 using the updated CCAMLR C2 and Observer data.

The estimated median stock size in block 58.4.4b_1 and 58.4.4b_2 was 380, and 483 tonnes, respectively, in Chapman estimator using R-package tagr. The estimated median stock size in block 58.4.4b_1 and 58.4.4b_2 was 1 057, and 1 153 tonnes, respectively, in CPUE analogy method (reference area: northern area of Subarea 48.4) using the relevant information of reference area (recent median CPUE, estimated biomass and updated area size) recommended by CCAMLR Secretariat in May 2016.

Predicted numbers of tag recaptures from the estimated stock sizes using both Chapman and CPUE analogy methods were generally inconsistent with the observed numbers for each block. The numbers using CPUE analogy method were generally closer to the observed ones for both blocks.

We propose to continue the current research operation for the next fishing season with the same survey design and total sample size of 60 tonnes in order to further strengthen the stock assessments in the area.