The reconciliation of CDS data with monthly fine-scale catch and effort data has demonstrated the effectiveness of the CDS to trace the catch of toothfish caught in the CCAMLR Convention Area. Whilst some variability has been observed amongst vessels, members have been contacted and dialogue is ongoing.

We update the estimates of the growth and length-weight parameters for Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea region (Subareas 88.1 and SSRUs 88.2AB). We present revised estimates of the von Bertalanffy growth curves, estimates of mean length at age using maximum likelihood estimation (MLE), and the length-weight relationship based on available CCAMLR SISO data collected from fishing operations in the Ross Sea region.

Estimates of growth and length-weight were similar to those previously used, however there was some suggestion that the shape of the growth curve may be better approximated by the MLE mean length at age relationship rather than by the von Bertalanffy equation. Stock assessment model estimates of B₀ and 2017 spawning stock biomass (B₂₀₁₇) and stock status (%SSB₂₀₁₇) were lower than with the previous von Bertalanffy relationship. But estimates of %SSB₂₀₁₇ were very similar between the revised von Bertalanffy and the MLE mean length at age model. In this case, the model conclusions were very similar and either of the updated relationships may be adequate parameterisations in the Ross Sea region stock assessment model.

Investigation of residual patterns in the fits to the relationships showed no evidence of systematic change in these parameters over time.

We provide diagnostic plots for the 2019 base case model for Antarctic toothfish in the Ross Sea region presented in Dunn (2019a), following the recommendations of WG-SAM-2015 (SC-CAMLR-XXXIV 2015 Annex 5). The stock assessment is described in Dunn (2019a) and a detailed description of the stock area, stock assessment methods and the stock assessment parameters are given in Dunn & Parker (2019b). Model inputs and a summary for the fishery up to the 2019 season are given in Devine et al. (2019). Associated CASAL data input (.csl files) and summary model output files (MPD and MCMC output) are available from CCAMLR Secretariat on request.

Stock Annex for the stock assessment of Ross Sea region Antarctic toothfish (Dissostichus mawsoni)

Species:    Antarctic toothfish (Dissostichus mawsoni)

Area:        Ross Sea (CCAMLR Subareas 881 & 882A-B)

Created:    1 October 2019

Authors:   Alistair Dunn and Steve Parker

Updated: October 2019

A Bayesian sex- and age-structured integrated stock assessment for Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea region (Subareas 88.1 and SSRUs 88.2A-B) is updated and revised using the most recent available data for the fishery. The assessment uses reported catch (C2), and tag-recapture data for 1998–2019 and age and abundance data from the Ross Sea Shelf survey for 2012–2019. Tag releases for 2001–2018 and commercial fishery age frequencies for 1998–2018 are also included.

Models estimates using the updated data for 1998–2017, new data from 2018 and 2019, revised growth and length-weight parameters, and a similar model structure as in 2017 estimated the equilibrium pre-exploitation spawning stock biomass to be about 71 730 t (95% CIs 65 890–78 730 t) and the current stock status to be 66% B₀ (63–69% B₀).

Model estimates of the pre-exploitation mature (spawning) stock biomass and current spawning stock biomass was slightly lower than that from the 2017 assessment due (i) to increases in the number of tags recaptures in 2018 and 2019; (ii) two years of additional fishing as the population approaches the target of 50% _B0; and (iii) revised length-weight and growth parameters. Sensitivity runs showed that the results were robust to assumptions of fleets-as-areas structure, older fish ogive choices, and the choice of tag dispersion rates. We also consider the recommendations from the CCAMLR Independent Stock Assessment Review for Toothfish in 2018, using updated growth and length-weight parameters, and sensitivities to estimate natural mortality and evaluate the effect of alternative levels of tag over-dispersion.

Overall, model fits to the data were adequate, and, as in previous assessments, the mark-recapture data provided the most information on stock abundance. Markov chain Monte-Carlo (MCMC) diagnostics suggested no evidence of non-convergence in the key biomass parameters. Patterns of residuals in the age-frequency proportions suggested some evidence of either strong and weak year class strength patterns before the period where year classes are estimated in the base model (2003–2013) or changing fishing selectivity over the course of the fishery. While sensitivity analyses suggested that these did not adversely impact estimates of current status, they should be investigated in future work

The precautionary yield using the CCAMLR decision rules and the applying catch split under CM 91-05 between north of 70° S (19%), south of 70° S (66%), and the SRZ (15%) was 3140 t. Hence, we recommend that the catch limit be set at a total 3140 t for the Ross Sea region in the 2019/20 and 2020/21 fishing seasons, with a catch limit of 588 t for north of 70° S, 2042 t for south of 70° S, and 464 t for the SRZ.

This report summarises fishing catch and effort in the Ross Sea region (Subarea 88.1 and SSRUs 88.2AB) together with biological characteristics of the catch of Antarctic toothfish through the 2019 season. The implementation of the Ross Sea Region Marine Protected area in December of 2017, concentrated fishing on the slope south of 70° S on the traditional fishing grounds, with some expansion of effort extending into SSRUs 88.2A and 88.2B, which are now open to fishing. Data are now summarized with respect to the current management areas.

The median and 90^th percentile of the scaled length distributions showed no trends in the different management areas; interannual variability is likely driven by spatial patterns in fishing. The strongest time trend in the data is the change in the sex ratio over time in the north, becoming gradually more male. The number of fish recaptured in 2019 was greater than in previous years; some fish were recaptured after 16 years at liberty. Recaptures were higher in 2019, likely a result of more tagged fish in the population and greater concentration of fishing effort on traditional fishing grounds.

This paper contains the report on outcomes of the work carried out by France and, in part by the CCAMLR Secretariat, proposed by France at CCAMLR-XXXVII, as endorsed by the Commission. The satellite overwatch project involved the receipt of images from target surveillance areas within the Convention Area, which were provided from the European Space Agency to the French Fisheries Maritime Control Center (FMCC). Part A of the paper reports on images analysed by the French FMCC containing a geographical position which were provided to the CCAMLR Secretariat for comparison with CCAMLR VMS data. The Secretariat was provided with 44 operable images, which corresponded with two CCAMLR authorised vessels. Part B of the paper reports on the analysis of AIS data carried out by the French agency CEREMA.

This paper provides analysis on the data collated by GLOBEFISH from publicly released sources for the trade of toothfish products for the 2018 calendar year. The analysis has identified that in 2018 toothfish was most commonly traded as an unprocessed frozen product which could be in various forms with mean unit values of 24.03 US$/kg for imports and 23.40 US$/kg for exports. The data identified the largest importer was the United States of America (USA), accounting for 36.50% of the global import market. The largest exporter was Chile accounting for 17.90% of the global export market. Application of the Max Partner Pair (MPP) estimation methodology identified the USA again as the largest importer, with 28.33% of global imports. France was estimated to be the largest exporter, with 18.61% of global exports. A comparison of the total quantity of toothfish products traded for imports and exports between global trade data and the CDS found that they are similar for imports with a 4.43%, but vastly different for exports with a 32.34% difference.

Gear loss as reported by longline vessels from the 2018 and 2019 fishing seasons, including differences in line loss by gear type, is reviewed following recommendations made at WG-FSA-18. Vessels reported 1 632 km of line lost in the Convention Area, of which 27% were complete lines. There was no difference in the relative reporting of lost hooks by gear type, with rates of loss recorded at 0.3% for each gear type for the past two seasons. There was a significant difference in the frequency of complete line loss between gear types, with a higher rate of complete line loss for trotline than for Spanish or autoline. It is important to improve reporting in order to accurately quantify rates of gear loss, and the associated environmental impact. It is also important to identify differences in gear design and fishing techniques that might influence rates of gear loss in longline fisheries.

The Republic of Korea would like to provide CCAMLR Members with further information, following-up to SCIC's request made in 2018 (SCIC-2018 Report, paragraph 81).