The crabeater seal, Lobodon carcinophaqus, is a species which appears to be useful as an indicator of marine. community interactions. Crabeater seals eat krill almost exclusively, live up to 40 years of age, have a circumpolar distribution and a large standing stock. The age at which crabeater seals reach sexual maturity is a parameter which might reflect changes in krill availability. Abundant food and relatively faster growth rates may lead to attaining sexual maturity earlier, decreased food availability would presumably have an opposite effect. The data on age at maturity previously published are reviewed in the light of recent material from the Antarctic Peninsula and an expanded sample. from Marguerite Bay. A correlation is demonstrated between Baleen whale catch data and seal maturity data from the study area. The age of sexual maturity in crabeater seals apparently decreased as a result of whaling and subsequently increased when whaling ceased. The causes of observed changes are likely to be related to complex interactions within the marine ecosystem. This study demonstrated the value of one aspect of crabeater seals as an indicator species. It is important that sampling of crabeater seals continue for monitoring studies of the Antarctic marine ecosystem.