SPATIAL PATTERNS IN MACKEREL ICEFISH DIET PROVIDES INSIGHTS INTO KRILL ABUNDANCE AND DISTRIBUTION

The diet of mackerel icefish was investigated from stomachs of 828 fish caught on the South Georgia and Shag Rocks shelves in January 2009. The results show that the diet of this normally krill-dependent species was dominated by the hyperiid amphipod Themisto gaudichaudii (92 % IRI) and was low in Antarctic krill (7 % IRI) compared with similar data for the same month in 2004-2006. The results are consistent with other indicators of krill availability on the South Georgia shelf, which indicate that the 2008/09 season was a particularly poor one for krill. Comparison of frequency of occurrence of krill in the diet with earlier data sets (1967-1992) show that 2009 is not unique, as similarly poor krill years occurred in 1969, 1978 and 1991. Spatial analysis of icefish diet indicates heterogeneity in the occurrence of prey, which is likely indicative of krill distribution. The utility of icefish diets as indicators of krill availability and distribution are considered.