CCAMLR

This document is based on the Research proposal for Dissostichus spp. in Subarea 48.1 by the Ukraine (WG-SAM-2019/28), which was presented and discussed at the meeting of the Working Group on Statistics on Statistics, Assessments and Modelling (Concarneau, France, 17 to 21 June 2019).

One of the outcomes of the Capacity-Building Workshop hosted by South Africa was the development of the applicable pro-forma and draft Deed of Funding. These documents are attached.

Information available in the CCEP on incidents of non-compliance with CM 26-01 paragraph 6, that prohibits dumping or discharging offal and discards south of 60°S, appear to be the result of mechanical failure. The information on offal management practices from other organisations relate to how and when offal should be discharged and largely reflects the provisions of CCAMLR’s CM 25-02, CM 25-03. The lack of a common theme in the relatively small (and declining) number of such reports do not indicate a specific action required to improve the implementation of CM 26-01 paragraph 6.

Electronic Monitoring on fishing vessels is increasing globally and is seen as an efficient method of assisting reliable reporting in commercial fisheries. These systems have been traditionally focused on the need to independently meet regulatory and market demands for transparency and accountability, but an increasingly important consideration is the contribution such systems can make to effective management by increasing the amount and quality of scientific research data that can be supplied from commercial fishing vessels.

This paper describes initial development work and presents several examples demonstrating the use of EM to collect research data in the CCAMLR managed Ross Sea toothfish fishery by New Zealand. Following the success of this work and other trials undertaken by other New Zealand vessels, we suggest that EM is further used to help provide better scientific research and monitoring data.

The Amundsen Sea region toothfish fishery has been operating since 2003. The biological characterisation of the fishery showed a truncation of the right-hand limb of the age distribution between 2004 and 2014. Few age data are currently available after 2014. We recommend that further ageing of toothfish in the ASR be made a priority to develop annual age-length keys and age frequencies. We further recommend that catch limits in the ASR be calculated following the trend analysis rules developed by WG-FSA for research blocks (CAMLR-XXXVI 2017, Annex 7 paragraph 4.33). The estimated catch limits, based on the one-year Chapman estimates and allowing a maximum of 20% in the catch limit for 88.2H and research block 882_2 are:

• 882H: 240 t catch and allowing a maximum of 20% change in the catch limit from 200 t.
• Research block 882_2: 288 t catch and allowing a maximum of 20% change in the catch limit from 240 t.

We note that research blocks 882_1, 3 and 4 used the CPUE by seabed area analogy in the past, which has been calculated by the CCAMLR Secretariat previously using the agreed method for research blocks in other areas. We have not updated the calculations in this report.

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.