Catch rates or catch per unit of effort (CPUE) are used for data-poor exploratory fisheries without integrated assessments in the CPUE by seabed area method to estimate stock biomass in the interim of collecting sufficient tag recaptures. Here, we address the two questions: (1) which unit of effort should be used for catch rates in mixed longline fisheries, and (2) how do different parameters such as gear type, vessel, fishing season, month, bait, fishing depth and area affect estimates of trend and magnitude of catch rates.

Using data from the Ross Sea Antarctic toothfish fishery, we compared effort units including length of line (km), total number of hooks per line, and a combination of total number of hooks per line for autoline and Spanish line and total number of clusters for trotline (hooks/cluster) with Generalised Linear Models (GLMs). The model with total hook numbers was preferred with the lowest Akaike’s Information Criterion (AIC), however standardised catch rates over the fishing season differed little between the models with the three effort units, so the effect of the choice of effort unit on the estimated standardised catch rates is small.

The parameters with the largest effects in the catch rate models were vessel, gear and bait, with vessels showing by far the largest effect size. This confirms previous advice that research fishing is conducted with a high level of spatial and temporal overlap between vessels and gear types to allow for a meaningful standardisation of variables such as catch rates.

To assist in future quality checking of data, we also recommend a new reporting field in the C2 form for the number of droplines per line deployed.

Robust stock assessments and catch limits for Dissostichus mawsoni 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 and WG-FSA-18/59 outlined the multi-member toothfish exploratory fishery research plans 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 2011/12 and 2018/19 fishing seasons, including the quantity of data and samples collected, as per Milestone 1.1 of WG-FSA-18/59. Reports relating to other research milestones for 2019 will be submitted to WG-FSA-19. The summaries provided herein were generated using an R-Markdown document which is available to Members to facilitate reporting on data collection in CCAMLR's Exploratory Fisheries.

This paper describes some of the planned updates to the 2019 integrated stock assessment for the Heard Island and McDonald Islands Patagonian toothfish (Dissostichus eleginoides) fishery in Division 58.5.2. These updates will include, inter alia, the estimation and inclusion of fishing mortality caused by longline gear loss, and an adjustment to the maturity function to be used in the assessment.

A field study is planned to validate the thorn ageing method for Antarctic starry skate (Amblyraja georgiana). This study is a fast, simple ‘add-on’ that will complement the aims of the skate tagging programme. The antibiotic terramycin (oxytetracycline hydrochloride, OTC) will be injected into skates brought into the boat for tagging during the 2019-20 skate tagging programme in the Ross Sea. Injections will be made intra-muscularly in the wings and/or the lateral tail base using a 1 ml auto-injector gun at a dose rate of 25 mg per kg of skate (± 10 mg/kg). Recaptured skates should be frozen whole, or a selection of caudal thorns removed and frozen, and returned to Wellington for lab analysis. The injection equipment and materials can be readily sourced from manufacturers provided by participating members. If necessary, New Zealand can provide injection equipment and terramycin to vessels transiting New Zealand prior to the 2019 fishery to encourage participation in this programme.

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.