Abstract: Antarctic krill (Euphausia superba Dana) were collected in the circumpolar region and in the Prydz Bay region of the Southern Ocean during the austral summer of 2007/2008 and 2008/2009, respectively, using a High Speed Collector and an IKMT net. The spatial distribution, population structure, and growing conditions of E. superba were studied with simultaneously measured environmental parameters. The abundance of E. superba was higher in the Weddell Sea than in Prydz Bay. The abundance of E. superba in both the Weddell Sea and Prydz Bay was lower than the abundance recorded in earlier surveys conducted during the same season (austral summer). Over the study area as a whole, E. superba showed normal growth during the two summer expeditions. However, at some stations, the growth of E. superba was limited, possibly as a result of delayed sea ice retreat or lower chlorophyll a concentrations. Analysis of the population structure of E. superba showed that juvenile krill accounted for a large proportion of the population at stations located near the edge of the sea ice, while adult krill predominated in stations in ice-free areas. This phenomenon reflects the different features of distribution between juvenile and adult krill. The population structure of E. superba varied among study areas, which may have affected the population recruitment.

Key words: Euphausia superba, population distribution, growing state, sea ice, Weddell Sea, Prydz Bay