CCAMLR

Exploratory fishing for toothfish (Dissostichus spp.) 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 outlines the first multi-member toothfish exploratory fishery research plan for East Antarctica, including research objectives, methods and milestones in accordance with ANNEX 24-01/A. In 2016, the Scientific Committee agreed that the research plan was appropriate to achieve its objectives (SC-CAMLR-XXXV, para. 3.244). We present here a proposal for the continuation of the research plan as set out in WG-FSA-16/29. All significant changes to the plan since 2016 are outlined in Section A, and changes made following WG-SAM-17 are highlighted in blue. Issues arising from the 2016/17 season are also provided in Section B.

Robust stock assessments and catch limits according to CCAMLR decision rules remain to be determined for Divisions 58.4.1 and 58.4.2, and precautionary management arrangements are in place as set out in Conservation Measures 41-11 and 41-05. WG-FSA-16/29 outlined the first multi-member toothfish exploratory fishery research plan for these Divisions, including research objectives, methods and milestones in accordance with ANNEX 24-01/A. In this paper we report on exploratory fishing activities undertaken by Australia, France, Japan, Republic of Korea and Spain between the 2012 and 2017 fishing seasons; including the quantity of data and samples collected, and an overview of progress toward research milestones. The associated research plan and reports relating to specific research milestones were submitted as companion papers. The summaries provided herein were generated using an R-Markdown document which can be made available to Members to facilitate reporting on data collection in CCAMLR's Exploratory Fisheries.

We provide an update of the Bayesian sex and age structured population stock assessment for Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea region (Subareas 88.1 and SSRUs 88.2A–B), using catch, catch-at-age, and tag-recapture data from 1998 to 2017 and including the results from the Ross Sea Shelf survey from 2012 to 2017. The model estimates of unfished biomass and current status were higher than that from the 2015 assessment. This was likely driven by the revised estimates of the effective tagging survival and tag detection rates, both of which have decreased in the recent years. Sensitivity runs showed that the results were relatively insensitive to the use of a logistic ogive rather than a domed ogive for fishing selectivity.

Model runs showed that the data from the Ross Sea Shelf survey were required to reliably estimate relative year class strengths. Year class strengths were estimated from 2003 to 2011 and showed two strong year classes and two weak year classes.

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.

The precautionary yield, using the CCAMLR decision rules and two potential catch splits between the Shelf, Slope, and North areas of the Ross Sea region consistent with previous fishing activities and with the Ross Sea region MPA, was either 3234 t or 3258 t. This yield is higher than that specified for 2018 in CM 91-05, which states that “the total catch limit shall be fixed at a level within the range of 2583 to 3157 tonnes per fishing season, based on advice from the Scientific Committee in 2017, 2018 and 2019” (CM 91-05 paragraph 28 (i)).

As the precautionary yield estimate is higher than the range specified in CM 91-05 for 2018, we therefore recommend that the catch limit be set at 3 157 tonnes for the 2018 and 2019 fishing seasons as per CM 91-05.