A multi-year, multi-Member research program was established to map and sample the fishable areas of SSRUs 88.2 A–B north of 66° S latitude. During the 6^th - 10^th February 2015, the UK fishing vessel Argos Froyanes surveyed SSRU 88.2 A research block 4 defined in the multi-Member 88.2 offshore research survey. Bathymetric data was collected and longline fishing conducted to release tagged fish and collect information on the characteristics of the toothfish inhabiting the region. The vessel set 7 longline sets with all vessel operations conforming to the required research criteria. A catch of 49 tonnes of D mawsoni and small catch of 29 kg of two D eleginoides was taken; 150 tagged fish were released at 3.1 fish tagged per tonne and a tag overlap statistic of 85%.

A link between D. eleginoides stocks in Subareas 48.3 and 48.4 has been speculated for some time. Different growth rates and maturity suggest that there is no regular exchange between the two areas, but tag recapture data clearly show a small number of toothfish moving between them, while genetic analysis also indicates that both stocks belong mostly to the same genetic population. Here we examine the information currently available. 

Characterisation of fishery selection is key to reducing uncertainty in the assessment and management advice provided for CCAMLR toothfish stocks. Toothfish migrate towards deeper waters as they age and increase in size and, in combination with the practical difficulties associated with deploying fishing gear at increasing depths, there is the potential for a dome shaped selection with age and size to arise. However this type of selection pattern is associated with the estimation of highly uncertain quantities of cryptic biomass. A review of the fishery and tagging data from the Patagonian toothfish (D. eleginoides) in Subarea 48.3 is used to determine whether there is sufficient information to determine the most likely fishery selection profile. A simple metric, the distribution of tag age with depth, is suggested as an indicator that a dome selection pattern is unlikely in the 48.3 fishery.   

Marine depredation (removal of fish from longline hooks by marine predators) is a growing issue in fisheries around the world. Within the CCAMLR management killer whales and to a lesser extent sperm whales cause greatest disruption to longline fishing activities for toothfish (Dissostichus sp.). Several measures have been developed and tested over the years to mitigate depredation by toothed whales, which include devices such as acoustic harassment devices (AHDs) emitting a deterring sound, the physical protection of the catch by nets, hooks or wires or changes in fishing practise such as moving to a different area when orcas are present, changing offal dumping practises or using lines of different length. However, deterrents and in particular acoustic deterrents have the potential to also affect non-target species such as fish, diving birds or pinnipeds. The different mitigation measures employed in the CCAMLR management area and their potential for disruption both in target and non-target species are reviewed below.

Depredation, the removal of fish from longlines by large marine predators, has been observed throughout the CCAMLR management area. Loss of fish through depredation can cause financial loss to the toothfish fishing industry and if not considered appropriately may lead to a bias in stock assessments through the underestimation of total mortality resulting from fishing and depredation combined. In some CCAMLR subareas this occurrence is well studied and included into stock assessments, while in other subareas the problem is known but not currently addressed. The areas in which the establishment of depredation has been studied have trialled a range of mitigation methods and developed approaches to minimize fishery-mammal interactions. This review summarises the current state of knowledge on depredation development and its impact on stock assessment, and concentrates on the four subareas that have either depredation occurring regularly or only sporadically but have the potential for development of a depredation situation, and could thus benefit of the methods and approaches tested in other subareas.

We made five sensitive runs of single-sex age-structured CASAL models for stock status assessments of Dissostichus eleginoides in the research block 58.4.4b_1 following the recommendation of the WG-FSA-2014 meeting. IUU catch was estimated within the models using disease mortality functionality. Firstly four sensitive runs were made as follows: 1) inclusion of all observations and estimate of same double normal selectivity for disease mortality and fishery (OB_1a model), 2) removal of tag and CPUE observations in 2008 from OB_1a model (OB_1b model), and 3) modified OB_1b model as fix of fishing selectivity at the estimates of OB_1b model, use of knife edge selectivity at fixed 8 year for disease mortality assuming IUU operations using gillnets, and weighting for tag and CPUE observations as per OB_1b model (OB_2b model). Next, further two sensitive runs based on OB_1b were made as follows: 4) removal of all tagging data (OB_1b_notag model) and 5) removal of age observations, and fix of both selectivitties at the estimates of OB_1b model (OB_1b_noage model).

The fits to CPUE in 2008 and MPD profiles for tags in the same year in OB_1a model were spurious. This suggests that Shinsei-maru No. 3 was learning operation in its first research in 2008. The removal of 2008 CPUE data improved the CPUE fits in OB_1b model. The fix of knife edge selectivity at 8 year for disease mortality in OB_2b model did not reduce the total objective function values compared to the original OB_1b model. The selectivity for IUU fishery likely represents the size of fish available for catches in this area.

The OB_1b_notag model did not improve any fits of observations. Although the CPUE fitted better than other models, the fits to tag data did not improve in OB_1b_noage model. The IUU estimate in 2013 for this model was unrealistically high.

From the results on MPD fits to observations, OB_1b model was considered as the most plausible model among five models. This model generally showed well convergence for each MCMC estimate.

The median MCMC estimates of the initial and current biomass were 1060 and 570 tonnes in OB_1b model. The CCAMLR yield was calculated at 51 tonnes. We recommend this model be used as management advice.

We made two sensitivity runs of age-structured and two fisheries (≥1300 m and < 1300 m) CASAL models for stock status assessments of Dissostichus eleginoides in the research block 58.4.3a_1 following the recommendations of the WG-FSA-2014 meeting. Two runs were carried out: including or excluding the data from fish tagged in 2012.

The likelihood profiles for tagged fish released in 2012 for ELAN_1 model reflected a large number of recaptures of the tags released concentrated in the western area of research block. This is why the removal of 2012 tag release data boosted the MPD estimate of B0 in ELAN_2 model. The selectivity of the shallow fishery is poorly estimated in MCMC runs for ELAN_1 model. This is unsurprising as the length frequency of the shallow fishery presents two shifting modes in most years, and therefore cannot be fully fitted.

We recommend that the more conservative model (including the 2012 tag data) be used for management purposes. The median MCMC estimates of the initial and current biomass were 560 and 420 tonnes and the CCMLR yield for this stock was calculated at 27t.

Following the recommendation of WG-FSA in 2014 the Secretariat has undertaken an analysis of by-catch in CCAMLR longline fisheries. The numerical target catch ratio (the number of target fish as a proportion of the total number of fish caught), using haul by haul data from the Ross Sea toothfish fishery from 2008–2014, was used as a single metric to examine the amount of by-catch reported by vessels. This analysis indicated that, as expected, differences in this index arose due to gear and location of fishing. However, there was also evidence of distinct differences in the mean (and distribution) in the index from two groups of Members flagged vessels, that together contribute 84% of the haul by haul data. These differences do not appear to be explained by differences in gear or location and are also apparent in the data reported by observers. However, the way in which observer sampling of by-catch is reported requires clarification. In order to further develop the analysis of by-catch it is essential to consider what additional factors need to be included in that analysis. This consideration should also review whether there have been any misinterpretations of the data, or the assumptions underlying the analysis, that may have led to errors in the results and subsequent interpretation.

Result of the Russian research program in the Subarea 48.5 (Weddell Sea) in season 2012-2013 were analysed in accordance with the Scientific Committee recommendations (CAMLR-SC-XXXIII, par. 3.230 – 3.234).

Russian Federation is going to continue investigation for toothfish in Ross Sea in fishing seasons 2015-2018. The present program aims to recapture tagged fishes released during the implementation of the previous research program took place in 2010-2012 fishing seasons and investigate resource potential and life cycle of Dissostichus species within the eastern part of the Ross Sea over shelf and continental slope within the Subarea 88.2 A.