CCAMLR

Ten hauling for Dissostichus eleginoides were performed from the 11lth to the 21 of April 1994, wich were related between them, when they contact within a circle of 10 nm of diameter, whose center was at 55° 03’ S 36° 53’ W. Leslie Method was applied to the data. initial biomass was projected to 3244.8 nm2, obtaining an estimated biomass of 937.8 ton. Due to statistical limitations of these data, another analisis based in the density (Kg/nm2) on the fished area was used. The positions given by the vessel were confirmed with information obtained from an automatic position system (ARGOS).

A total of 63 hauls and 10 oceanographical legs were obtained. Of these, 44 hauls taken in Subarea 48.3 on a random stratified des n are used to estimate the standing stocks of the main commercial fish species along different methods, as well as their length frequency distributions. A change in surface water temperature of about -0.5 to -1.0 in a period of approximately 20 days was detected around South Georgia Islands. In the Scotia Sea the boundary of the Weddell-Scotia confluence was found within historical limits while surface water (down to 50/70 meters) was warmer than expected. It was also found that the spatial structure of fish populations significantly affects the results of biomass estimates.

A preliminary histological analysis on the ovarian development in Champsocephalus gunnari was carried out. Six stages of oocytary development were identified and are similar to those described for other species. A gonad maturation scale was elaborated and adapted to the macroscopic scale commonly used. Oocytary resorption processes were observed during ovarian maturation. In some cases the ovaries presented few atretic oocytes ; in others a generalized regression was found. In the southwest portion of the South Georgia shelf, 50 % of the ovaries exhibited a pre-reproductive regression stage similar to that reported for the same species in the 1991 summer season.

The diet composition of the icefish Champsocephalus gunnari caught in the Subarea 48.3 in February/March 1994 was analyzed using the frequency of occurrence (%) method. Krill (Euphausia superba) followed by the amphipod hyperiid Themisto gaudichaudii were the main prey items at South Georgia and Shag Rocks; fish were found in the stomachs more frequently than in past seasons around South Georgia, in parallel with the virtual absence of mysids and Thysanoessa spp.. Krill was available for fish in common levels, equivalent to those of previous years (e.g. 1985, 1992). However, high proportions of empty stomachs were found at South Georgia and Shag Rocks, close to the values reported for the 1991 year of krill "shortage". Besides, the tentative analysis of part of the samples using the coefficient Q (%) showed a greater importance of T. gaudichaudii with respect to krill. It is possible that the inconsistencies found between the results obtained by both methods are due to a particular spatial distribution of krill in the area in the period of study, but no previous data are available for comparison. No krill aggregations were found in the region by acoustic methods in the 1994 summer season; a fact that might be related with a significant change in surface temperature observed during the cruise.

At the 1993 meeting of the Working Group on Fish Stock Assessment, members requested that work be undertaken to evaluate certain aspects of the experimental management strategy for the Antarctic crab fishery. A simulation model is proposed for conducting this work. Length frequency and catch rate data from the 1991/92 crab fishery are used to motivate the construction of an ontogenetic migration model for describing crab distribution, movement, and recruitment during the simulation. The fishery simulation is spatially explicit, and the dynamics of crab abundance are described on a daily basis. The simulation includes advective and diffusive movement rates, a lagged Beverton-Holt stock recruitment relationship, and a model for catch that contains a random normal deviate. Finally, an algorithm is developed for describing the spatial and temporal distribution of fishing effort during the simulation. This algorithm is based on the idea that each fishing vessel constructs a map of expected catch rates across the fishing grounds. Each vessel updates this expectation map on a daily basis and uses it to determine the distribution of targeted fishing effort and searching effort.

From the end of March to the beginning of May. 1993, during fishing operations for krill conducted by the m/t Lepus on the fishing grounds off South Orkney Islands: and South Georgia, investigations were• carried out to determine biological/fisheries characteristics of the exploited stocks. One of their goals was to determine the proportion of juvenile fish forms in krill concentrations. The present study gives the results of these observations. It appears from the investigations that the by-catch of juvenile fish in the krill fishery was small. and off South Orkney Islands there was no such by-catch at all in the samples collected. In both areas a small by-catch from the family Myctophidae was observed.

Methods for the calculation of the horizontal opening (swept area) of a bottom trawl are discussed. Details of the Scanmar trawl monitoring equipment used for making in situ measurements of horizontal opening and headline height of the FP-1 20 trawl during the 1993/94 UK fish stock assessment survey around South Georgia on the MV Cordella are provided. Empirical equations are derived for the calculation of horizontal opening from other, more easily obtained measurements, such as tow speed and trawI depth. A new multiple regression equation is compared to that used previously for the estimation of biomass parameters of the major fish species around South Georgia. The resulting difference in biomass estimates is of the order of a 1% to 5% increase, depending upon species.