Japan and France revised the next season’s (2017/18) research plan in research blocks 58.4.4b_1 and 58.4.4b_2 using the latest CCAMLR C2 and Observer data, following several advices during WG-SAM meeting in 2017. We have used extracted data provided by the CCAMLR Secretariat on 27th July, 2017.

The estimated median stock size in block 58.4.4b_1 and 58.4.4b_2 was 1452.03 and 921.91, tonnes respectively, in Chapman method considering tags released in the last three years as effective for the biomass estimation. The estimated median stock size in block 58.4.4b_1 and 58.4.4b_2 was 484.51 and 498.76 tonnes, respectively, in CPUE analogy method (reference area: HIMI) using the relevant information of reference area (recent median CPUE, estimated biomass and updated area size) recommended in the WG-SAM-16/18 Rev.1.

We propose to continue the current research operation for the next fishing season with the same survey design and total catch limit of 70 tonnes to further strengthen the stock assessments in the area.

The ratio of female among the 600 specimens of Antarctic toothfish collected from the 58.4.1 area and 88.3 area within the CCAMLR Conservation Zone during February through March, 2013 was found to be 0.50, and displayed the tendency of increase with increase in the total length 140 cm. The gonadosomatic index of the fish was 2.5 for the female, and 1.7 for male.  The hepatosomatic index of female (2.5) and male (2.7) were similar. The type of ovarian development of Antarctic toothfish was group-synchronous type. In the ovaries of growing stage, initial vitellogenic oocytes with approximately 150 ㎛ of egg size was observed mainly. The egg size of mature oocytes presented approximately 800 ㎛e. As the result of H-E staining, eosinophilic yolk materials and vacuolar oil droplets were interspersed within the cytoplasm. The egg size of ripe oocytes were approximately 1,000 ㎛. Eosinophilic yolk materials are distributed within the medulla of cytoplasm, and combined multiple vacuolar oil droplets were existed in the cortical section of the cytoplasm. Histological testicular type of Antarctic toothfish was testicular lobule type, and the testicular lobule was composed of numerous testicular cysts. In the testis of growing stage the cysts became more definite gradually, and spermatogonia and spermatocytes occupied most of the cortex of the testicular lobule. It was possible to observe spermatids that illustrated basophilic reaction in H-E staining within the expanded testicular cysts in the mature stage. In the ripe stage, inner cavity of testicular lobules was occupied by spermatozoa of basophilic in H-E stain. Frequency of ovarian development stages of Antarctic toothfish showed the highest proportion with 45.4% at the ripe stage, and followed by the growing stage with 25.9% and mature stage with 28.7%. Frequency of testicular developmental stages demonstrated the highest proportion with 67.0% for the matuer stage, and followed by growing stage with 24.2% and ripe stage with 9.9%. The group maturity in accordance with the total length (TL) categories of Antarctic toothfish displayed 80% for female in larger than TL 100 cm categories and almost 100% for male in larger than TL 150 cm categories.

South Africa and Japan revised the next season’s (2017/18) research plan in Subarea 48.6 using the latest CCAMLR C2 and Observer data, following the recommendations and notification from WG-SAM meeting in 2017 (e.g., WG-SAM-17 report, paragraph 4.4, 4.10, and 4.18, 2017) and data extracts provided by the CCAMLR Secretariat on the 27th of July, 2017 were used.

The estimated median stock sizes in research blocks 48.6_2E (southeast part of 48.6_2), 48.6_3, and 48.6_4 are 4864.30, 3132.55, and 8044.33 tonnes, respectively, when applying the Chapman method. Chapman method considers tags that were released in the most recent year as effective for the biomass estimation, except for 48.6_4 which considered the last three years when estimating biomass. The estimated median stock sizes in blocks 48.6_2W, 48.6_2E, 48.6_3, and 48.6_4 were 189.56, 306.31, 125.05, and 969.14 tonnes, respectively, when CPUE by sea bed area methods are used considering the relevant information of reference area (recent median CPUE, estimated biomass and updated area size) recommended in the WG-SAM-16/18 Rev.1.

We propose to continue the current research operation in Subarea 48.6 for the next fishing season with the same survey design. 

Following the note by the Working Group in paragraph 4.21 in WG-SAM-17 report on the ice concentration analysis by Namba et al. (WG-SAM-17/10), the further analyses for the ice concentration was conducted to investigate correlations between sea-ice coverage and wider global weather phenomena such as El Niño/El Niño Southern Oscillation or rising temperatures/increased variability in the sea surface temperature (SST) anomaly (variance from average) of ERDDAP of NOAA.

Stomach contents of the Antarctic toothfish, Dissostichus mawsoni, collected from Subareas 58.4 and 88.3 were analyzed using next generation sequencing (NGS) technology. After processing the raw reads generated by the MiSeq platform, a total of 131,233 contigs (130 operational taxonomic units [OTUs]) were obtained from 163 individuals in subarea 58.4, and 75,961 contigs (105 OTUs) from 164 fish in subarea 88.3. At 98 % sequence identity, species names were assigned to most OTUs in this study, indicating the quality of the DNA barcode database for the Antarctic Ocean was sufficient for molecular analysis, especially for fish species. A total of 19 species was identified from the stomach of D. mawsoni in this study, which included 14 fish species and 5 mollusks. More than 90 % of contigs belonged to fish species, supporting the postulate that the major prey of D. mawsoni are fish. Two fish species, Macrourus whitsoni and Chionobathyscus dewitti, were the most important prey items (a finding similar to that of previous studies). We also obtained genotypes of prey items by NGS analysis, identifying an additional 17 representative haplotypes in this study. Comparison with three previous morphological studies and the NGS-based molecular identification in this study extended our knowledge regarding the prey of D. mawsoni, which previously was not possible. These results suggested that NGS-based diet studies are possible, if several current technical limitations, including the quality of the barcode database or the development of precise molecular quantification techniques to link them with morphological values, are overcome. To achieve this, additional studies should be conducted on various marine organisms.

In the present study, the concentrations of total mercury in different organs of the Antarctic toothfish (Dissostichus mawsoni) collected from CCAMLR research blocks in Subarea 88.3 and Division 58.4.1 off the coast of Antarctica were determined. The results revealed total mercury concentrations of 0.165 ± 0.095 mg/kg (0.023–0.454 mg/kg) in the Antarctic toothfish. In fish muscle, methylmercury accounted for approximately 40% of the total mercury. In a comparison analysis, muscle and liver tended to bioaccumulate the highest levels of total mercury, and both total mercury and methylmercury contents showed correlations with fish length and weight. Compared with international guidelines, fish contained 2.5–6.4% and 4.0–10.3% of the provisional tolerable weekly intake for total mercury recommended by the Joint FAO/WHO Expert Committee on Food Additives and the tolerable weekly intake for methylmercury proposed by the European Food Safety Authority, respectively. These results suggest that consumption of the Antarctic toothfish presents no health risk to humans.

This report summarises fishing catch and effort in the Ross Sea region (Subarea 88.1 and SSRUs 882AB) together with biological characteristics of the catch of Antarctic toothfish through the 2017 season. In 2017, sea ice constraints were minimal and catch rates were the second highest on record, resulting in the shortest season to since the fishery started.

Median and 90%ile scaled lengths show no trend on the Shelf, Slope or North. Age frequencies show no uniform trend and are probably driven by location of fishing. The strongest time trend in the data is the change in the sex ratio over time in all three locations.

The catch limits for macrourid and skates are dictated by CM 41-09. Because the areas open to fishing will change in 2018, with the implementation of the Ross Sea region Marine Protected Area (CM 91-05), we recommend catch limit for bycatch species for the North, Slope and SRZ areas based on methods used to set those limits in the past.