Analysis of the diet of Champsocephalus gunnari at South Georgia in late summer from 1994 to 1997, Dr Eduardo L. Holmberg surveys
The diet composition of the mackerel icefish (Champsocephalus gunnari) caught in CCAMLR Subarea 48.3 in late summer from 1994 to 1997 was analysed using frequency of occurrence (F%) and dietary 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 species in the diet of C. gunnari was reversed. The consumption of other prey items such as mysids and Thysanoessa sp., which are known to be important alternative food in years of krill scarcity, as well as fish, was only occasional or negligible and varied from year to year. The spatial distribution of the main prey items in the diet of C. gunnari, as well as of the proportions of stomachs with/without food in Subarea 48.3, did not show a consistent pattern from year to year. Likewise, in the four surveys by the Dr Eduardo L. Holinberg from 1994 to 1997, high proportions of fish had empty stomachs, a phenomenon which could be caused by several concurrent factors. The variation of the diet according to the length of C. gunnari did not reveal any selectivity pattern for any of the prey items. The availability of krill in Subarea 48.3 during the period investigated can be defined as low in 1994 (equivalent to years of krill scarcity), intermediate in 1995 (below years of historically high abundance), and high in 1996 and 1997 (in line with years of high krill abundance). This information is well in accord with independent information from acoustic surveys and krill-dependent species monitored under the CCAMLR Ecosystem Monitoring Program (CEMP).