Biotopic and spatial distribution of krill Euphausia superba Dana (Crustacea, Euphausiacea) length groupings in the Atlantic sector of Antarctic in summer 1984 and 1988

Three basic length groupings of krill were identified with the clustering analysis on the basis of the data of two complex surveys carried out in the western Atlantic sector of Antarctic in summer 1984 and 1988. The large-length grouping is biotopically associated with the waters of the southern branch of the Antarctic Circumpolar Current (ACC). The middle-length grouping and the small-length grouping are associated with the Weddell Sea waters. Besides, the additional fourth grouping with bimodal length structure was revealed in the survey 1988. It is assumed that the first grouping is transported into the area from the Pacific sector, while the second and the third groupings are of local origin and the forth one is formed as a result of mixing of the groupings inhabiting different biotopes under the impact of the secondary frontal zone dynamic conditions. Hydrometeorological conditions in summer 1988 complied with the climatic norm and seemed to stipulate the typical pattern of krill spatial distribution. The different distribution pattern observed during the survey 1984 was related to intensification of ACC and reduction of the Weddell waters intrusion into the eastern Scotia Sea. The comparative analysis of the survey results in 1984, 1988 and CCMLR-2000 showed that krill population structure in the western Atlantic sector of Antarctic has not actually changed.