Stable carbon and nitrogen isotope ratios in whiskers and blood of young (2-3 years old) and sub-adult (4-7 years old) Antarctic fur seal males from the South Shetland Islands were used to assess the seasonal and interannual changes in the krill contribution to their diet. The dataset shows the stable isotope ratios revealing that krill dominated the diet of young and sub-adult male Antarctic fur seals year-round, with penguins, and not fish, as the second major prey, regardless of year and season. Whisker values are represented from the oldest part of the whisker (tip) to the newest one (root).