Aspects of the reproductive performance of Black-browed, Grey-headed and Wandering Albatrossess, Gentoo and Macaroni Penguins and Antarctic Fur Seals, recorded annually at Bird Island, South Georgia over the last decade (and similar data for Adelie and Chinstrap Penguins at Signy Island, South Orkney Islands) are summarised and reviewed. Breeding success of the Wandering Albatross, which breeds in winter and eats fish and squid, has remained constant, while population size has declined gradually but significantly. The other species at South Georgia, which breed in summer and for which krill forms a significant proportion of their diet, have shown major fluctuations in some or all of: breeding population size, breeding success, foraging trip duration and offspring growth rate. 1977-78 and 1983-84 were summers of particularly poor reproductive performance by almost all species. Difficulties in provisioning offspring were mainly responsible; circumstantial evidence relating this to reduced availability of krill is discussed. The fluctuations in reproductive performance of the krill-eating, summer-breeding penguins at Signy Island are not synchronised with those at South Georgia. They correlate best (and especially for Chinstraps, which suffered badly in 1980-81 and 1982-83) with the date of ice break-out in late spring. Detailed comparisons between normal and abnormal years are made of a range of parameters of albatross, penguin and fur seal biology. The results are reviewed in terms of their suitability for detecting changes in the marine environment that may relate to prey availability and thus be influenced by commercial harvesting.