A preliminary integrated stock assessment model was constructed for Dissostichus mawsoni at the Subarea 48.6, using the data collected from Research blocks 2 – 5. Our model showed some improvements, especially in the age/tagging related assumptions. On the other hands, we found some unexpected results on CPUE fits and MPD profiles, which should be carefully considered before we move on to the next step. Additional data or arrangement of parameters of CASAL model might help us to improve the model quality to conduct the future stock assessment of D. mawsoni in subarea 48.6.

We report the progress on the development of statistical modeling to estimate abundance trends of bycatch species (grenadiers) caught by longline fisheries in CCAMLR Subarea 48.6 using a spatial delta-GLMM implemented by the R package VAST. In response to the comments from WG-FSA-2020 e-group discussions, separate models were constructed for all research blocks within the subarea, and the residuals diagnostics were examined. Although we successfully estimated indices of abundance and the estimation was robust to the choice of covariates, further examinations and improvements are required, given the result of model diagnostics.

During three fishing seasons 2018/19, 2019/20 and 2020/21 Ukrainian vessel CALIPSO (shipowner FC NEPTUNO LLC, Ukraine) tried to perform the research survey in the statistical subarea 48.1 according to the research plans and annual management advices of the working groups FSA and Scientific Committee meetings. All three surveys were interrupted before the completion of research objectives. The first season of the research, the problem was concerned accessibility of fishing grounds due to sea-ice, the second and the third seasons of the research by-catch limit of Macrourus spp. was reached before the surveys were completed. Nevertheless, there were collected a large number of diverse scientific data on pelagic and benthic ecosystems, including high quality underwater footage, video monitoring of hauling lines and also photo and video fixation of tagged toothfish releasing.

Reducing fish and invertebrate by-catch in targeted fisheries is an element of a precautionary approach to the management of Antarctic living resources. At the same time establishing by-catch limits sometimes could block in fact the research activities in certain marine areas. It is  a reason to consider establishing by-catch limits for each separate research survey taking into account a research approach, abandoning the universal approach like reflected in the Conservation Measure 33-03.

The Scientific Committee considered the assessment of Dissostichus spp. in data-poor fisheries to be of a high priority (SC-CAMLR-XXIX, paragraphs 3.125 to 3.145). The use of different gear types for the implementation of a multi-Member research on Dissostichus spp. in East Antarctica (Divisions 58.4.1 and 58.4.2) in the seasons 2011/12 - 2017/18 is a critical factor for their   efficiency and reliability. In the context of the discussion of the Scientific Committee (SC-CAMLR-XXXVII p.3.338-3.144; SC-CAMLR-XXXVIII p. 318, 3.119; SC-CAMLR-XXXIX p.4.10) we propose the research program on Dissostichus spp by the  multi-vessels  in Divisions 58.4.1  for seasons 2021/22-2023/24 based on standardized   sampling longline gear  and survey stratified  design.  

Fishing for Patagonian toothfish (Dissostichus eleginoides) has been carried out  in Subarea 48.3  continually for more than 40 years, including more than 25 years under CCAMLR management. This paper reviews the long-term decline in the size structure of Patagonian toothfish (Dissostichus eleginoides) observed in longline catches taken in Subarea 48.3. It was noted  that from the start of the 2000s until now, longline fishing in Subarea 48.3  has targeted immature fish smaller than 100 cm. The issue of non-rational use of the Patagonian toothfish stock in Subarea 48.3 is examined

The SC-CAMLR last estimated a precautionary harvest rate (gamma) used for management advice in the Area 48 krill fisheries in 2007 (SC-CAMLR, 2007 Annex 4 paras. 2.38-2.39). Subsequently, a range of various methods have been tried, with limited success, to produce both input parameters and stock assessments which can be used for management advice. Following the work plan outlined by SC-CAMLR (2019, Annex 4 paras. 2.60 – 2.64) endorsed by the Commission (CCAMLR, 2019, para. 5.53) the Generalised Yield Model (GYM) software was reimplemented in R as the Grym package, with the intention of updating the previous krill assessment. However, the methods used to estimate some input parameters to the previous assessment were not documented in detail, and there remains considerable ambiguity as to how to compute these inputs, and how these inputs are used within the assessment simulations.

Here we aim to clarify what each parameter within the Grym models are used for, and where possible provide examples as to how they have been calculated.

WG-SAM-2021 and WG-EMM-2021 reviewed available information for krill assessment simulations in Subarea 48.1 using the Grym. Whilst no agreement on parameters was achieved at WG-SAM-2021, the Working Group agreed that an ensemble approach using multiple parameter value combinations could be used (WG-SAM-2021, paras 3.21-3.22.)

WG-EMM-2021 provided initial parameters for the assessment simulations noting that alternate parameters could be tested to compare (WG-EMM-2021, paras 2.32-2.33 and Table 1).

Here we present the results of model ensembles for values either provided directly to the CCAMLR e-group on ‘GYM/Grym assessment model development’, or calculated based upon data submitted to the e-group.  Code and outputs of the models are available on github (https://github.com/ccamlr/Grym_Base_Case /tree/Simulations).

A collaborative research program has been undertaken by Japan and South Africa since 2013 to enhance data collection and analysis in the subarea 48.6 under CM 21-02. Spain joined the proposal starting from 2018/19 fishing season in order to contribute to the data acquisition and to speed up the integrated assessments of the Antarctic toothfish (Dissostichus mawsoni) stock in this subarea (WG-FSA-18/34).

The continuation of the three-member research proposal for 2021/22 season is presented to ensure continuity of previous research activities. Data and investigations about the population structure and various demographic parameters of D. mawsoni using trotline (JPN and ZAF) and Spanish longline (ESP) gears, established tagging techniques, pop-up tags and genetic analysis will provide the basis for the development of spatial population models and assessments in support of management advice. An Integrated Stock Assessment (ISA) which takes into account the tag time series from southern research areas of Subarea 48.6 is going to be continually developed until the end of the 2023/24 season.

Based on suggestion from WG-SAM-2021 (report of WG-SAM-2021, para 8.4), the research plan have been revised as follows:

• Explaining the importance of understanding stock connectivity between research blocks in the area (seamounts versus continental shelf),
• indicating further details about how the stock structure will be represented in the planned CASAL assessment for the region,
• increasing the otolith sampling rate from “10 otoliths per 5 cm length bin” to “20 otolith per 5 cm length bin), and
• indicating minimum sampling requirements for by-catch species and designed to meet the research objectives.

The WG-SAM-2021 recalled that a structured fishing design was necessary to optimise tagging performance evaluation (report of WG-SAM-2021, para 8.4). However, as already described in 3(a) “Research survey/fishing design”, the area is not suitable to set a stratified sampling design as the fishing grounds with broad environmental characteristics such as a complex of seamounts, hills and ridges is expected to be small relative to the size of the research block. Therefore, no depth stratification is proposed in the current research plan.

The updated CCAMLR Research Plan – Research Proponent Self-Assessment can be found in Appendix 1.