The South Georgia population of mackerel icefish (Champsocephalus gunnari) is exploited by both a fishery and predators, including gentoo penguins (Pygoscelis papua). Because considerable uncertainty surrounds recent estimates of stock size, there is a need to consider novel approaches that may give insight into the population dynamics of this species. We derive two indices of recruitment based on the occurrence of mackerel icefish in gentoo penguin diets, one of which is scaled by a survey estimate of the density of Antarctic krill (Euphausia superba), an alternative prey species for gentoo penguins. The closure of the fishery for much of the 1990s allowed the relationship between environmental conditions and recruitment to be studied without the confounding effects of fishing mortality. The recruitment indices were positively correlated with sea surface temperature with a lag time equal to the age of the fish. These results suggest strong links between mesoscale environmental processes and the smaller scale interaction between gentoo penguins and their mackerel icefish prey.