Winter gut contents of the Antarctic krill (Euphausia superba Dana) collected in the South Georgia area

Foregut contents of the Antarctic krill Euphausia superba Dana which were collected in the South Georgia area in austral winter, 12 July ~ 4 August 1992 were observed. A total of 130 individuals (adults: 78, subadults: 49, juveniles: 3) which were caught by krill trawling from various depths were examined in this study. The foregut contents of the krill consisted of various fragments of crustacean zooplankton in 77 individuals out of 130 examined. Among the fragments a portion of the pereiopods of krill was found from all specimens examined. Although the obtained materials were geographically confined to the South Georgian waters, which was free from fast ice throughout the year, the results might imply that E. superba seemed to seasonally switch their food source: E. superba demonstrated herbivorous food habits during the rich phytoplankton bloom, but might change to carnivorous habits in the fall and winter. Strong cannibalistic food habits during austral winter as found in this study are considered to be important aspects for the population dynamics of krill.