SPATIAL VARIABILITY OF ANTARCTIC KRILL IN RELATION TO MESOSCALE HYDROGRAPHY

To examine the mesoscale distribution of Antarctic krill Euphausia sup erba Dana, length frequency and maturity stage data were subjected to multivariate analysis. The results showed that the population was hete rogeneous with respect to size and maturity, with small immature krill found primarily inside the Bransfield Strait and large mature krill m ainly north of the South Shetland Islands. Multivariate analysis of hy drographic data collected at the same stations revealed that the ocean ography corresponded to previous classifications of the area, with Wed dell Sea water in the southeast and east and South East Pacific water in the northwest. Further multivariate analysis using both krill varia bility and hydrographic data showed that a strong correlation existed between the krill distribution and the oceanography. Several hypothese s to explain the observed distribution of krill are discussed. It is j udged that neither simple processes, such as growth during the samplin g period, nor processes whereby krill are advected passively through t he area by water movement, can completely explain the observed distrib ution. Instead, it is concluded that the observed gradient of krill si ze and maturity probably arises, at least in part, from an active onto genetic migration.