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.
Abstract:
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.
