Variations in food composition and feeding intensity of mackerel icefish (Champsocephalus gunnari) at South Georgia

The diet composition and feeding intensity of mackerel icefish (Champsocephalus gunnari) around Shag Rocks and the mainland of South Georgia was investigated in January/February 1985, January/February 1991 and January 1992 by analyzing appr. 9,000 stomachs. Main prey items were krill (Euphausia superba), the hyperiid Themisto gaudichaudii, mysids and in 1985 also Thysanoessa species. The proportion of krill and Themisto in the diet items varied considerably between the three seasons, whereas the proportion of mysids in the diet remained fairly constant. krill is obviously the prefered diet. In years of krill shortage, such as in 1991, krill is replaced by Themisto gaudichaudii and sometimes Thysanoessa. Variation in food composition between sampling sites was high. This high variation can be primarily attributed to differences in prey availability, but appears to be much less influenced by differences in length composition of the fish between sampling stations. Feeding intensity varied also considerably between seasons. It was highest in 1992.