CCAMLR

We propose to conduct an exploratory satellite tagging campaign of Patagonian toothfish (Dissostichus eleginoides) in the Southwest Atlantic Ocean (FAO Area 41). Existing data on this species is extremely rare and incomplete in both study duration and geographic coverage. This proposal attempts to address this inadequacy by deploying a total of 50 popup satellite archival tags on mature, adult Patagonian toothfish over two fishing years. Since this work is highly exploratory and will represent one of the first dedicated research effort on this species, we have developed an adaptive experimental design in flexibly targeting specimens according to fish availability and fishing conditions. Our goal is to provide a first description of both short-term, and ideally, long-term horizontal movements of Patagonian toothfish. This work has the potential to reveal the possible connectivity among various parts of the Southern Ocean that has eluded all previous work.

The scientific survey was conducted by the Greenstar (KOR) in the research block 883_1–883_P9. Due to extreme ice conditions covering the southern part of 88.3, Janas (NZL) was not able to conduct its part of the survey. The total catch of D. mawsoni was 63,840 kg comprising 2,526 individuals. The CPUE for Dissostichus mawsoni indicated regional differences among the research blocks. CPUE was similar in research blocks 883_1, 883_3 and 883_4 with the range of 0.1110–0.1571, but much lower in research block 883_5, 883_P8, 883_P9 with the range of 0–0.0185. Tagging rate and tag overlap in Subarea 88.3 were 5.4 fish per tonne and 87%. The length frequency of D. mawsoni exhibited a bimodal distribution with modes near 70 cm and 150–160cm. Proportions for female maturity stages 1, 2, and 3 were similar, showing 33.3%, 37.1%, and 29.4%, respectively, whereas proportions for male maturity stages 1 and 2 accounted for 42.2% and 55.9%, respectively. Regional differences in female and male maturities were observed with stage 1 and 2. Otolith, stomach contents, gonad, fin and muscle samples were collected to obtain biological information of D. mawsoni.

We report a preliminary result of statistical modeling of grenadier bycatch pattern by bottom longline research fisheries in CCAMLR Subarea 48.6, using generalized linear mixed models with zero-inflation. The result contains several issues including the failure of estimation in considerable number of candidate models, overdispersion and insufficient prediction of zero-catch, suggesting that further improvement is required.

Division 58.4.4b has been a closed area since 2002 (CM 32-02) and scientific research has been conducted with a research plan submitted under CM 24-01 since 2008 by Japan. France joined this research plan in 2015 and a joint proposal was submitted for the first time in 2016 (WG-SAM-16/06 and WG-FSA-16/33 Rev. 1) for a period of 5 years.

The proposal submitted here has been substantially revised to address the concerns expressed at WG-FSA 2019 and SC-CAMLR-XXXVII (para. 3.158). We followed and improved the revised research plan presented in SC-CAMLR-XXXVII Annex 12 and redefined slightly the research objectives. The survey design has been amended to avoid sea pen hotspots in the eastern part of 58.4.4b_2 (WG-FSA-18/23) and a new French vessel has joined the research plan to increase research survey capacity.

Toothfish population structure and bycatch analyses will be presented at WG-FSA-19, while the main concerns regarding objective 2 (“Provide an assessment of the status and productivity of Patagonian toothfish stock”) and 5 (“Contribute to scientific research programs on killer whales (O. orca) ecology and depredation”) are addressed in two documents submitted at WG-SAM-19.

We updated toothfish biological parameters (growth curve, maturity ogive, ALK) using >2000 age readings and incorporated estimations of depredation rate and IUU into an integrated stock assessment model. We built up the CASAL model developed in WG-FSA-15/23 by Taki et al. (2015). Different scenarios of depredation and IUU were tested to account for uncertainties associated with these processes in the model. In parallel, we standardized toothfish CPUE to explore temporal trends.

Results on killer whales depredation revealed a lower effect than previously estimated due to the absence of interaction in recent years and the low historical interaction and depredation rates in the research blocks b_1 and b_2. Analyses of killer whales photo-identification provided new insights on movements and population dynamics in the South Indian Ocean.

We made significant progress on the stock assessment and clarified objectives and milestones to facilitate the reviewing process of this research plan. A list of dates by which specific milestones will be completed and reported to CCAMLR working groups was provided and a final report will be provided at WG-FSA in 2021.

The introduction of the Ross Sea region Marine Protected Area has elevated the need for research (including fisheries research) to inform the Research and Monitoring Plan and to evaluate the effectiveness of the Marine Protected Area. All research should be based on a robust experimental design, and in particular, fisheries research within the Ross Sea region should:

1. meet a high standard of experimental design;
2. derive the maximum scientific outcomes from proposed activities; and
3. ensure that robust scientific conclusions can be drawn from the outcomes.

To meet this challenge, we provide a guide for the preparation and evaluation of fisheries research that will interact with the Ross Sea region Marine Protected Area. These include design aspects such as strata definition, catch rate standardisation, vessel calibration, station randomisation, and power analyses, as well as implementation aspects such as data collection requirements. These aspects of design are critical to ensure robust scientific conclusions concerning, for example, local area fish abundance, life history attributes, and ecosystem structure and function.

The CCAMLR Tagging Programme is a key part of CCAMLR’s management of toothfish fisheries and linking the details of recaptured fish to that of tagged fish is a key element of the programme. The CCAMLR Secretariat has developed a new tag linking approach that is designed to provide greater flexibility in linking recaptures to releases, including where a recapture is linked with equal probability to multiple releases. This new approach uses more of the available data to increase the level of transparency and provides an index of the level of confidence in all linked mark-recapture data.

The Secretariat requests advice from the Members on processes for deprecating the existing tag-linking approach and transitioning to the new routine as the default tag linking method used by the Secretariat. In particular, the Secretariat seeks guidance from Members that use toothfish tagging data on any additional descriptions and diagnostics that could be provided to facilitate the adoption of this change in tag-linking approach.

Exploratory fishing for toothfish (Dissostichus mawsoni) in East Antarctica (Divisions 58.4.1 and 58.4.2) began in 2003. Robust stock assessments and catch limits according to CCAMLR decision rules remain to be determined for these Divisions. WG-FSA-16/29 outlined the first multi-member toothfish exploratory fishery research plan up to 2017/18 for East Antarctica, which the Scientific Committee agreed was appropriate to achieve the research objectives (SC-CAMLR 2016, para. 3.244). Subsequent research progress including the evaluation of standard approaches to identify precautionary catch limits (WG-FSA-17 para. 4.28-4.38) and bycatch mitigation (Maschette et al. 2017), suggests a low risk profile for this fishery. Furthermore, examination of bycatch data and underwater video footage have not led to the identification of vulnerable marine ecosystem (VME) indicator species (Maschette et al. 2017, Eléaume et al. 2018). Here, we update the research plan for 2018/19 to 2021/22 (WG-FSA-18/59), in accordance with ANNEX 24-01/A, Format 2. This plan has been designed as a 4-year plan, based on the low risk profile of this fishery and to allow more time for review by Working Groups of major reporting and review years in non-stock-assessment years.

Compared to last year (WG-FSA-18/59), this research plan has been updated with 2019/20 operating details, the inclusion of modelling work under Objective 2, and a re-ordering of milestones under Objective 4.

Natural mortality (M) is a key parameter in fisheries stock assessments, relating directly to the productivity of a stock, stock status, and estimated precautionary yields. In the Ross Sea region stock assessment for Antarctic toothfish (Dissostichus mawsoni), M is assumed to be 0.13 y^-1 and constant across age and sex.

In 2018, the independent review of the Ross Sea region D. mawsoni stock assessment recommended that CCAMLR consider the robustness and reliability of estimating natural mortality in the stock assessment model. We undertake a preliminary investigation of estimating natural mortality using the assessment model from the Ross Sea region from 2017.

We estimated natural mortality as a single value for males and females combined, with a uniform prior within the base model used in 2017 for Antarctic toothfish in the Ross Sea region. The model MCMCs estimated M=0.11 y^-1 (0.09–0.13 y^-1) with B0 estimated to be 92 140 t (70 330–121 950 t); a higher B0 72 620 t (65 040–81 050 t) when compared to the 2017 base case where M=0.13 y^-1. The precision of the estimate of B₀ when estimating natural mortality was lower and estimated the precautionary yield higher (3419 t compared with 3258 t). MPD simulations suggested that when the rate of natural mortality was assumed in an operating model, it was estimated with relatively high precision and with no bias.

Further investigations will need to be carried out to consider the effect on model fits and residuals and if robust estimates of the rate of natural mortality can be achieved using MCMC simulations. We recommend that analyses exploring the effect of the model-based estimate of M, including values of natural mortality that vary by age and sex, should be considered in future stock assessment sensitivity analyses