This study tested hypotheses relating the foraging trip durations of lactating female Antarctic fur seals, to the abundance and availability of Antarctic krill, where the mean length of krill consumed is used a proxy of krill availability. Over six years, 1568 foraging trips were measured for 178 individual seals, foraging from Bird Island, South Georgia. The relationships between the duration of these trips and the mean length of krill, derived from scat samples, was then investigated. This study has shown large-scale changes in the krill population around South Georgia are easily detected in the foraging trip duration of female lactating Antarctic fur seals. The study found a positive correlation between foraging trip duration and the krill length, suggesting that longer trips, reflecting lower krill availability, are associated with a greater mean size of krill. This study illustrates the important potential for predators, specifically female Antarctic fur seals, as samplers of a highly variable marine environment.