The annual random stratified trawl survey was undertaken in Division 58.5.2 in the vicinity of Heard Island and McDonald Islands during April 2018. This paper provides an updated growth model and a preliminary assessment for mackerel icefish (Champsocephalus gunnari) population structure, abundance and yield in Division 58.5.2 to the west of 79^o 20’ E using standard CCAMLR methods (CMIX and Generalized Yield Model).

The 2018 survey showed a large 2+ cohort in the population. Catches of 443 t in the 2018/19 season and 320 t in the 2019/20 season respectively satisfied the CCAMLR decision rules.

The annual random stratified trawl survey (RSTS) of 2018 around Heard Island and McDonald Island (HIMI) in Division 58.5.2 took place from the end of March to the end of April, with the completion of 163 stations plus eight extra fine mesh hauls. The survey was conducted on the FV Atlas Cove. Sampling protocols such as the design and the duration of the hauls were similar to recent surveys, but with a new set of randomly selected station points.

The catch of Dissostichus eleginoides (Patagonian toothfish) was twice that of 2017 while the catch of Champsocephalus gunnari (mackerel icefish) was two thirds of the 2017 survey catches. The catches of the other managed bycatch species, Channichthys rhinoceratus (unicorn icefish), Lepidonotothen squamifrons (grey rockcod) and Macrourus spp. (macrourids combined) were also two to three times greater than those of last year. Catches of skates were similar to those of 2017. Invertebrate catch (including jellyfish) in the 2018 survey was 1.5 times the low value of 2017.

The calculated biomass for 2018 of the target species D. eleginoides and C. gunnari in the survey area were close to the highest estimates for the past 10 years. For the managed by-catch species C. rhinoceratus and Macrourus spp. the biomass estimate was similarly high. Conversely, the estimate for L. squamifrons has been low for the past 4 years. The 2018 biomass estimates for each of the three Bathyraja spp. (skates) were the highest in the last 10 years.

Length measurements and sex were taken for nearly 22 000 fish and for more than half of those biological measurements were also recorded. Otoliths were collected from 656 D. eleginoides and 609 individuals were tagged and released.

During the 2017/18 season the Spanish F/V Tronio fished in Statistical Subarea 88.1 and Division 58.4.1 where the latter area required a tag rate of five fish per ton greenweight caught and also where the overall size of the fish exceeds 115cm. The tagging station on the FV Tronio is on the upper deck above the hauling station providing easy access to retrieve smaller fish directly from the hauling station and to operate the cradle over the side for landing larger fish. To optimise the use of the cradle a series of modifications were trialed to optimize the handling of the cradle, achieve rapid retrieval to minimize hauling downtime, minimize handling and time out of the water of the fish and use the cradle to release the fish. The modification achieved most of these objectives, with room for some further suggested alteration to further improve the system.

In the present study a comparative morphometric analysis of sagittal otoliths was performed in three Channichthyids (Pseudochaenichthys georgianus, Chaenocephalus aceratus and Chaenocephalus gunnari) collected during a research survey carried out between January 23 and February 13, 2016, along the continental shelf and slope around Elephant Island (Subarea 48.1) and the South Orkney Islands (Subarea 48.2). Morphometric analysis was addressed using Basic size descriptors (BSD; area & perimeter), shape indices (SI; circularity, squareness and roundness) and elliptical Fourier Descriptors (EFD) on 2D binarized images of left and right otoliths for fish ranging from 20 to 67 cm TL. To test for significant differences between the left and right sagittae in BSDs, a univariate and multivariate ANOVA and MANOVA were used, with BDSs as dependent variables and otolith type as fixed factor. ANOVA and MANOVA showed all standardized BSDs did not varied significantly between right and left sagittae (P>0.05). All EFDs derived from the 20 harmonics analyzed were homoscedastic and normal, and showed very low level of correlation among them. Hence, all coefficients were used in MANOVA and LFDA. MANOVA showed significant differences in the contour between both otolith pairs for each species (p<0.001). Similarly, EFS coefficients showed a high discriminatory power to distinguish the left and right otoliths, with a total percentage of correct classification of 76, 96, and 89% for P. georgeanus, C. gunnari and C. aceratus. A link between the extreme environmental conditions of Antarctic waters and the occurrence of the unusual high asymmetry in the otolith contour is proposed for Channichthyids and its implications are discussed.

In the present study we provide new insights on the spatial distribution and population structure of juvenile D. mawsoni caught during bottom trawl survey on the shelves around the South Shetland Islands (CCAMLR Subarea 48.1). Fish samples were collected during five summer cruises conducted from 2001 to 2007. Juveniles were relatively evenly distributed on the shelves around Elephant Island and northern lower South Shetland Islands. Although they were caught in all depth strata, they were most abundant between 100 and 300 m depth. The sampled population was composed of 150 specimens measuring between 22 and 78 cm TL, equally distributed between sexes, most of them with gonads at immature stage of maturity. Both males and females showed a positive allometric body growth, suggesting a good condition factor. Based on counts of annual growth increments from sagittal otolith sections, age estimates ranged between 2 and 7 years in males and between 2 and 8 years in females, respectively. Annual growth rate was estimated from the age-length keys, spanning from 10 to 5 cm TL. Present data have been discussed in comparison with the biological traits of adults reported elsewhere.

A research plan for this subarea was commenced by Korea in 2016 and a revised collaborative proposal was submitted to WG-FSA-17 by Korea and New Zealand. This joint research proposal was for an additional 3 years covering the period 2018, 2019 and 2020. It was designed to build on Korea’s previous research by continuing to focus on those research blocks where tagged fish have previously been released on the slope, whilst also prospecting two of the northern seamount complexes and two boxes on the southern shelf, where little or no fishing has occurred. The main objective of the proposal is to determine the abundance of Antarctic toothfish in Subarea 88.3. Secondary objectives are to improve understanding of stock structure of toothfish in this area, to carry out calibration trials between the two vessels, to collect data on the spatial and depth distributions of bycatch species, and to trial electronic monitoring using video cameras. This paper updates the proposal with an amendment to include a catch redistribution mechanism and to incorporate a milestone table as recommended by WG-SAM-18.

This paper proposes to continue the Ross Sea shelf toothfish survey for the next five years, 2018–2022. The first objective of the survey is to monitor toothfish recruitment in the southern Ross Sea (core strata). This is a continuation of the yearly time series of research surveys of these strata carried out since 2012. It is important to continue the time series as the data collected provide essential input to the stock assessment to estimate year class strength which is used to inform management decisions. The second objective is to monitor trends in larger (large sub-adult and adult) toothfish abundance in alternate years in McMurdo Sound and Terra Nova Bay where toothfish may form an important part of the diet of Type C killer whales and Weddell seals. The third objective is to collect and analyse a wide range of data and samples from these areas (e.g. benthic invertebrates, stomach and tissue samples, and acoustic data). Both objectives two and three are specified as high priority research topics in the research and monitoring plan for the Ross Sea region MPA. The survey design will remain consistent with previous years. Different catch limits are requested on alternate year to account for the different catch rates in McMurdo Sound and Terra Nova Bay. The results of each survey and trends in the time series will be presented to WG-FSA for review each year and the results included in the stock assessment. A full review will be completed and presented to WG-SAM, WG-EMM, and WG-FSA in 2022. This revised proposal incorporates the milestone tracking table recommended by WG-SAM-18.

We propose to test three hypotheses to describe the reproductive ecology of Antarctic toothfish (Dissostichus mawsoni):

1) Antarctic toothfish eggs are buoyant and accumulate under sea ice. If true, this would retain eggs near the spawning locations under the vast sea ice extent and once broken up in the spring, may provide access to a productive pagophilic ecosystem for feeding as well as a transport mechanism for subsequent advection patterns, all of which could be impacted by climate change. This would have implications on the understanding where recruiting fish originate and how those patterns may be influenced by changes in sea ice or circulation patterns that affect observed recruitment patterns.

2) Antarctic toothfish spawn throughout the Pacific Antarctic fracture zone. Evidence to date only exists from the west of the region (SSRU 881B), yet adult Antarctic toothfish are found much further east and north of the CCAMLR Convention Area, which is bounded by latitude 60°S. Obtaining a better understanding of the location and movement of adult spawning toothfish has direct implications on the understanding of those parts of the adult stock that contribute to recruitment, and hence the productivity of the stock assumed in the stock assessment.

3) Biological characteristics of the northern spawning population change as younger, fatter, female fish move to the north for spawning during winter. Evidence to date found no change in these characteristics in June, suggesting sampling later in the spawning season is needed.

We propose to conduct a scientific survey during the austral winter in the northern Ross Sea region to test these hypotheses. The longline and plankton survey is designed to cover key gaps in the knowledge of the life cycle of Antarctic toothfish in the Ross Sea by collecting biological samples from a range of locations in the northern regions of Subarea 88.1 and 88.2 and begin in September 2019. The survey will be coordinated with a corresponding survey targeting Antarctic toothfish spawning dynamics in the southern area of the South Pacific Regional Fisheries Management Organisation (SPRFMO) area at a similar time. This revised proposal details the catch accounting method proposed by WG-SAM-18 and incorporates the milestone tracking table.

The New Zealand vessel San Aspiring carried out an exploratory research program for toothfish in the South Pacific Regional Fisheries Management Organisation (SPRFMO) Convention Area during August 2016 (Fenaughty et al. 2016) and September 2017. Analysis of the information collected showed high catch rates of post-spawning Antarctic toothfish, similar in magnitude to catch rates in the north region of CCAMLR subareas 88.1 and 88.2. The toothfish catch was almost entirely Antarctic toothfish except for two juvenile Patagonian toothfish. Sex ratios showed a high proportion of males to females. Fish were in poor body condition as assessed using Fulton’s condition factor indicative of full or partial starvation which would be consistent with a spawning event prior to the sampling in 2016 and 2017. Body condition was slightly better in 2017 when sampling occurred about 5 weeks later than in 2016. Fish length and mass, body condition, sex ratio, and gonad condition were consistent with previous observations from the northern Ross Sea region in CCAMLR Subareas 88.1 and 88.2 (Fenaughty 2006, Fenaughty et al. 2008, Parker & Marriott 2012, Stevens et al. 2016).

These results give a strong indication that Antarctic toothfish also spawn north of 60° south latitude in the Southern Ocean. Biological measurements collected from fish sampled in this SPRFMO area of study are consistent with previous information and analyses from the northern regions of CCAMLR Subarea 88.1, indicative of spawning in that region suggesting that Antarctic toothfish spawning may extend over a wider geographic area than initially hypothesised.

This paper presents further progress towards an integrated stock assessment model for Antarctic toothfish (Dissostichus mawsoni) in the Amundsen Sea region, defined here as SSRUs 88.2C–H. The region is split into two areas: the North (SSRU 88.2H) comprising large mature fish, and the South (SSRUs 88.2C–G) comprising a mix of large mature fish and small immature fish.

Two-area stock assessment models were first developed for the region in 2014 and refined in 2015 and 2016. Results showed the need to collect mark-recapture data in the South to inform the estimation of biomass in the South. Simulation work undertaken in 2017 showed that if tag recaptures continued in the south, and were spread among research blocks, a model may be developed for management advice.

We present an update on these two-area stock models including data from four years of recapture data from the South. The assessment models were fit to the proportions-at-age in the catch, and the mark-recapture data from the two areas. The results suggest that data from the research plan are starting to inform the model, especially with respect to the size of the population in the south and migration rates between areas. Biomass estimates are in agreement with those calculated using local Chapman and CPUE by seabed area analogy methods. At this stage the model should only be used as indicative due to issues including poor fit to the age data in the south, the lack of year-specific age frequency data to inform these fits, and the limited spatial extent of the tag recaptures in the South (almost all recaptures in research block 882_2).

We recommend that the analyses be developed to incorporate the spatial distribution of the tagged fish and subsequent fishing effort, as well as further investigations of the distribution of fish in relation to their length. We also recommend that all Members contribute validated age data from otoliths collected in Subarea 88.2 to further inform the understanding of the stock, and that the research data from vessels that have lower effective tag survival and detection be significantly improved to ensure the best use of the available information.