CCAMLR

On the basis of analyses and review of published data on the biology and distribution of Electrona carlsbergi, as well as on the hydrological patterns of the Southern Ocean - especially concerning the structure and spatial variation of the Antarctic Circumpolar Current (ACC) - this paper describes possible ways and means (mechanisms) by which this species carries out meridional migration in various frontal zones. The yearly transport of E. carlsbergi into the waters of the Southern Polar Frontal Zone (SPFZ) occurs regularly although its intensity changes in time. The densest concentrations are observed here in the spring-summer period (November to February) when zooplankton. the main dietary component for E. carlsbergi, is undergoing rapid development. In various areas of the SPFZ and in all sectors of Antarctica E. carlsbergi is represented by immature specimens 7 to 8 cm in length and 2 years of age, indicating dominance by a single cohort. Moreover, a very similar size composition in the SPFZ is evident from both a seasonal and interannual point of view. The proportion of immature specimens in the Subantarctic zone, classified as a breeding area, decreases to 20-40%, while the number of mature specimens 8.5-11 cm in length and 3-5 years old increases. Based on the dynamic processes of the Southern Ocean and taking account of the locations of spawning areas and distribution of E. carlsbergi in the early stages of its life cycle, a theory has been put forward concerning the presence in the notal region and various sectors of Antarctica of several reproductive zones coinciding with areas of large scale disruptions to the zonality of transport by the ACC under the influence of topogenic factors. This paper examines the fate of large swarms (in terms of biomass) of E. carlsbergi transported beyond the notal region and the possibility of a part of the population returning to the reproductive zone. There is a strong likelihood that E. carlsbergi migrates from the SPFZ into the Subantarctic zone by means of eddy formations which occur periodically in the ACC system. These eddies play an important role in the meridional exchange of waters between frontal zones. The paper also discusses questions of the within-species structure of E. carlsbergi and an ecological assessment of the impact of fishing on the ecosystem of the open waters of Antarctica.

Analysis and synthesis of results of Russian and foreign research into the trophic relationships of myctophids demonstrate that this group of mesopelagic fish plays a significant role in the community of marine organisms of the Southern Ocean. The trophic status of myctophids has been determined - they are zooplankton-eaters who consume a considerable amount of meso and macroplankton which determines their high abundance and biomass. Thus, according to a preliminary estimate the yearly consumption of zooplankton by Electrona carlsbergi, the most numerous species of myctophid, ranges from 196 to 364 million tonnes. According to its position in the trophic system of the Southern Ocean, myctophids occupy the third trophic level and are consumers of the second order. Myctophids play a major role as producers, in turn guaranteeing the production of organisms at higher trophic levels (certain species of squid, notothenoids, sea birds and mammals). The large deepwater squid Mesonychoteuthis hamiltoni each year consumes approximately 48 to 57 million tonnes of myctophids. A summary table of the trophic relationships of myctophids is presented, based on general patterns of energy transformation from one trophic level to the next.

The Kerguelen fishery (trawlers and long-liners) of Dissostichus eleginoides is analyzed in the ligth of the knowledge of life cycle of the species. Catches reach a similar cumulative value that in South Georgia subarea (48-3). Fishing grounds and fishing methods have been separated and the tendancies from the LFD and an index of abundance compared.

Patagonian toothfish, Dissostichus eleginoides, spawn in July to September. Hatching is likely to occur in October/November. Scales do not start to form before the fish are 64-74 mm long. It is far from being resolved when the first 'winter ring' is formed. Available information suggests that the annulus may not be completed before spring. Length composition of fish

Samples of fish collected from 1983 to 1992 at Potter Cove, King George Island, South Shetland Islands, are used to study the decline in abundance previously reported fro fjord Notothenia rossii, in association with changes in the size and age structure of the juvenile population. Mean lengths increased in correlation with poor recruitment to inshore waters and sharply decreased as stronger year classes entered the cove. In comparison, Notothenia neglecta, a non commercially fished species with similar ecological habits in the fjords, showed little variations around the expected overall mean size, without any significant trend. Thus, the changes in the juvenile N. rossii population are not thought to be caused by local factors, but related with the operations of the commercial fishery during the late seventies in the area, mainly around Elephant Island. Data from 1991 and 1992 might be indicating the beginning of a recovery of the N. rossii population in Potter cove.

The paper presents calculations of water flow velocity through the codend under the assumption that the flow is uniform and equal on its entire surface. The calculations were made for different ratios of cod end length to its diameter, mesh bar length to mesh bar diameter, and for various mesh opening coefficients. The results obtained were analysed with regard to the impact of flow velocity on hydrodynamic forces opening the codend. These forces, different for different cod end constructions, have great impact on selection properties. The greater velocity of water outflow is effecting the wider opening of the codend meshes and a greater probability of undersized - juvenile fish escaping.
An idea of a new setup of meshes in the codend, changing the effect of operation of longitudinal forces (hydromechanical drag forces) was presented. Closing forces become mesh opening forces, which should ensure greater mesh opening coefficient and better selectivity of the codend of the trawl.

The Antarctic fish fauna is relatively impoverished with fewer than 300 species recorded from the whole Southern Ocean. Demersal forms predominate but many of these have extended early life histories as pelagic larval and juvenile phases. Only 30 larval stages of the 103 fish species occurring at South Georgia have been identified but these represent all of the dominant and economically important forms. The larval stages occur in succession throughout the year suggesting niche separation to avoid competition. The ichthyoplankton distribution exhibits a marked division between oceanic and neritic coincident with the continental shelf-break. The neritic larval assemblages are more diverse and abundant with greater proximity to the coast. Studies on ichthyoplankton temporal distribution in the fjord, East Cumberland Bay, and the adjacent shelf areas at South Georgia show both large seasonal variations and marked interannual variations in species composition and abundance. The mechanisms controlling the larval fish assemblages are not known but the observed interannual variations must reflect interactions within the neritic ecosystem and so have important implications for subsequent recruitment at South Georgia. By-catch of young fish during the krill fishery further perturbate recruitment success and may delay the recovery of fish populations from over-exploitation by commerical-scale fin-fisheries over the past 30 years.