Analysis of the diet of Champsocephalus gunnari in Subarea 48.3, in late summer of years 1994–97, Dr E. Holmberg surveys

The diet composition of mackerel icefish Champsocephalus gunnari caught in Subarea 48.3 in late summer of years 1994-97 was analysed using frequency of occurrence (F%) and coefficient "Q" (%) methods. Krill (Euphausia superba) followed by the amphipod hyperiid Themisto gaudichaudii was the main food item around South Georgia and Shag Rocks in the period investigated, except in 1994, when the order of importance of these two organisms in the diet was inverted. The consumption of other prey items such as mysids and Thysanoessa sp., which are known as important alternative food in years of krill scarcity and fish, was only occasional or in negligible amounts, showing interannual variation. The spatial distribution of the main preys in the diet as well as of the proportions of stomachs with/without food in the area of investigation didn't show a consistent pattern from year to year. Likewise, in the four Holmberg 1944-1997 surveys, high proportions of fish exhibited empty stomachs, phenomenon for which non consistent explanation was found. The variation of the diet with respect to the length of C. gunnari didn't show a selectivity pattern for any of the prey items. The availability of krill in the Statistical Subarea 48.3 in the period investigated can be defined as low in 1944, equivalent to those years of krill scarcity; intermediate in 1995, below the historical years of high abundance; and high in 1946 and 1997, in line with the years of krill richness. This information is well in accord with independent information from acoustic surveys and krill dependent species monitored in the CEMP.