Following the Spanish research plan approved by the SC-CCAMLR XXXII, during the third year of the multi-year research survey in the Division 58.4.1, as far as the ice condition allowed, the F/V Tronio has returned to the same places surveyed in the previous seasons and a prospection all along the area has been carried on.

Preliminary results of the last 2015/16 season survey are presented together with a comparative analysis of the three-seasons carried out in this division. A depletion experiment has been made in each of the prospected SSRUs. Results in SSRUs 5841H and G are not conclusive. Likewise tag-recapture results have been poorer than expected. Accessibility problems by the ice cover and traces of IUU fishing found in the proposed areas might have great influence in the results.

The IEO continues reading of otoliths for ageing Antarctic toothfish. These data will be added to the input data in the near future in order to carry out an integrated assessment of Dissostichus mawsoni stocks in this Division.   

Results of other data collected such as fish bycatch or incidental catch of benthic taxa are also presented.

The condition and survival of Antarctic krill (Euphausia superba) strongly depends on sea ice during winter. How krill utilize sea ice depends on several factors such as region and developmental stage. A comprehensive understanding of sea ice habitat use by krill, however, remains largely unknown. The aim of this study was to improve the understanding of the krill's interaction with the sea ice habitat during winter/early spring by conducting large-scale sampling of the ice-water interface (0-2 m) and comparing the size and developmental stage composition of krill with the pelagic population (0-500 m). Results show that the population in the Northern Weddell Sea consisted mainly of krill that were <1 year old (age class 0; AC0), and that it was comprised of multiple cohorts. Size per developmental stage differed spatially, indicating that the krill were likely advected from various origins. The size distribution of krill differed between the two depth strata sampled. Larval stages with a relatively small size (mean 7-8 mm) dominated the upper two meter layer of the water column, while larger larvae and ACO juveniles (mean 14-15) were proportionally more abundant in the o-500 m stratum. Our results show that, as krill mature, their vertical distribution and utilization of the sea ice appear to change gradually. This could be the result of changes in physiology and/or behaviour, as, e.g., the krill's energy demand and swimming capacity increase with size and age. The degree of sea ice association will have an effect on large-scale distribution patterns of AC0 krill and on predictions of the consequences of sea ice decline on their survival over winter.

In recent years there have been a number of changes in the criteria, metrics and application of methods used in setting research catch limits in research blocks as well as assessing progress in research plans. This has resulted in some confusion in the application of methods and the intended purpose of the metrics included in the summary table presented to the Scientific Committee that includes recommended research catch limits. Given the importance of this table, and the need to ensure clarity in the methods used to generate and update the data included therein, the Secretariat was requested to update the summary table using the most recent data available and to detail the methods used for local biomass estimation (SC-CAMLR-XXXIV, paragraph 3.232 (i)). This paper provides an updated summary table, with a full description of the methods used in that updated table, as well as some history of decisions made by WG-FSA in developing the overall approach. Challenges encountered when updating the metrics in the summary table are detailed along with points that might require further clarity and consideration by WG-SAM and WG-FSA. 

The most common and widespread salp in the Southern Ocean is Salpa thompsoni. It is characterized by a circumpolar distribution and its appearance is clearly associated with the occurrence of the Antarctic Circumpolar Current (ACC). This area of the Southern Ocean is characterized by a relatively low productivity and high water temperature. In recent years the expansion of distribution range of this invertebrate species has been observed. This process may be a result of the ACC southward movement, which is caused by ocean warming and variability in sea ice extent. The presented time series is based on samples collected between 1975 and 2001 in the region of Western Antarctic Peninsula. The results of laboratory analyses, coupled with environmental data, obtained both during sampling and from satellite data, allowed to prove that the distribution of salps was significantly correlated with water temperature and presence of sea-ice, while their abundance resulted from salinity and temperature. The results of our study suggest that with climatic changes, such as temperature increase and reduction of sea-ice cover, the distribution range and abundance of Salpa thompsoni is likely to increase in the Western Antarctic.

Feedback Management (FBM) requires adequate data that can be collected with a minimum of extra effort. Traditional survey practice requires a pre determined survey design that support statistical handling of the collected data into stock abundance information. Godø et al. (2015) (WG-EMM-15/13) show the inherent variability of catch and acoustic data collected during fishing operation. At the same time the data might inform about patterns in the ecosystem of importance to FBM. Similarly, Niklitschek and Skaret (2015) (EMM-16 doc) utilize spatial statistics to show that fisheries acoustic data recorded during regular fishing operations give consistent information about spatial and temporal distribution and abundance of krill in the South Orkney Islands. However, due to the lack of survey design there is an unknown impact/uncertainty of the effect of using data collected during aimed trawling at high krill concentrations.  It is suggested that combining their approach with a conventional design might inform about some of this uncertainties. In this paper we discuss how the information of these two papers can be used in an operational FBM.

There is a substantial harvestfor Antarctic krill in the Southern Ocean, butlittle regular scientific monitoring of the resource. Recently, however, the Commission for the Conservation of Marine Living Resources (CCAMLR) has initialised a process to make use of acoustic data from commercial fisheries to increase the amount of relevant information available for making management decisions. We here provide an example where 34 days of acoustic data, collected during commercial krill fishing operations on the vessel ‘Saga Sea’ were processed to produce probability of presence, conditional density and relative abundance estimates on monthly, weekly and daily basis. Data were analyzed using a maximum likelihood time-series and geostatistical approaches, selected to account for the lack of sampling design, and likely correlation in space and time. The applied method showed low sensitivity of monthly estimates to different repeated measure criteria and location sub-settings. Most weekly estimates, but the last one, were also consistent with the full data (monthly) estimate. Highly variable and lower estimates were obtained, however, from daily data sets. Although our results suggest the method had provided an adequate treatment for time and space correlation, we were not able to evaluate potential bias due to preferential sampling of high density krill aggregations and/or limited area coverage within short time periods. The results suggest that this method, combined with some additional design based coverage by the fishing vessels, can be useful to obtain quantitative evaluations of krill density and distribution for management purposes.

Weather extremes are one important element of ongoing climate change, but their impacts are poorly understood because they are, by definition, rare events. If the frequency and severity of extreme weather events increase, there is an urgent need to understand and predict the ecological consequences of such events. In this study, we aimed to quantify the effects of snow storms on nest survival in Antarctic petrels and assess whether snow storms are an important driver of annual breeding success and population growth rate. We used detailed data on daily individual nest survival in a year with frequent and heavy snow storms, and long term data on petrel productivity (i.e., number of chicks pro- duced) at the colony level. Our results indicated that snow storms are an important determinant of nest survival and overall productivity. Snow storm events explained 30% of the daily nest survival within the 2011/2012 season and nearly 30% of the interannual variation in colony productivity in period 1985–2014. Snow storms are a key driver of Antarctic petrel breeding success, and potentially population dynamics. We also found state-dependent effects of snow storms and chicks in poor condition were more likely to die during a snow storm than chicks in good condition. This stresses the importance of con- sidering interactions between individual heterogeneity and extreme weather events to understand both individual and population responses to climate change.