Seasonal and inter-annual variability in the distribution of Electrona carlsbergi in the southern Polar Front area (the area to the north of South Georgia is used as an example)

摘要

From 1987 to 1989 VNIRO (USSR) conducted six trawl and acoustic surveys in the area to the north of South Georgia Is between 49° to 54°S and 25° to 40°W. The area is within the Polar Frontal Zone where mesopelagic fish from the family Myctophidae are found most frequently and regularly. Seasonal and inter-annual variability in distribution, density and biomass of the most abundant species of myctophids, Electrona carlsbergi, are analyzed and summarized in this paper. The species is also known to form large concentrations throughout the year. Results of surveys showed that the distribution and behaviour of E. carlsbergi are strongly related to environmental conditions in the area as well as to the availability and distribution of zooplankton. E. carlsbergi was found over the entire study area. The largest concentrations of the species, however, were found mainly along edges of the frontal zone where such fundamental environmental characteristics of water masses as currency dynamics, temperature and density, attain the highest level of variation. The most large-scale and dense concentrations of E. carlsbergi were observed in summer (December to February) when fish were distributed in the upper 50-100 m layer. The smallest and less dense concentrations were observed in the winter (June) at 200 m and deeper. The spring and autumn months were noted as transitional for parameters of vertical distribution and density of fish concentrations. Calculations of biomass of E. carlsbergi in the area indicated that its variability during the year is related to parameters of spatial and vertical distribution of fish. Interannual variability of E. carlsbergi biomass in the area was also observed.