Changes in some seabird populations at Marion Island

Abstract

South Africa's Prince Edward Islands are important breeding localities for sub­ Antarctic seabirds, the conservation status of several of which is of concern1. At Marion Island, for some species, assessments of the numbers breeding and of breeding success have been made since 1994/95. Four penguin species breed at this island. For the far-ranging king penguin Aptenodytes patagonicus, the production of chicks fluctuated around a stable leveI2. Estimates of the population sizes of the other three penguins decreased, most severely for the two that feed closest to the island while breeding: gentoo Pygoscelis papua and rockhopper Eudyptes chrysocome penguins3 5. The two Eudyptes penguins (rockhopper and macaroni E. chrysolophus) leave the island during winter. For these two species, trends in the numbers breeding at specific colonies were well correlated6. The times of arrival of females for breeding, and for rockhopper penguins the mass of females on arrival, were significantly related to breeding success6. These results suggest that over-wintering conditions influence both the proportion of mature birds that breed and breeding success6; hence, attempts are being made to identify the winter feeding grounds. The Crozet shag Phalacrocorax melanogenis, another bird with a limited foraging range, also suffered a severe decrease7. The decreases of some of the seabirds are thought at least partially attributable to inadequate breeding success, suggesting poor feeding conditions around the island during the breeding season3 5 7. Long-term environmental change may be influencing prey availability near the island and at winter feeding grounds. To the north, off South Africa, an eastward displacement of sardine Sardinops sagax, an important forage fish for seabirds, has resulted in a mismatch in the distributions of the breeding localities and prey of seabirds, and recent large decreases of African penguins Spheniscus demersus8. At Marion Island, the populations of some species of albatross and petrel, which travel substantial distances away from the islands, have shown a long-term decrease1. These birds are at risk from mortality in high seas and continental fisheries9. As with penguins, it is necessary to establish the at-sea distributions of several of the albatrosses and petrels that breed at Marion Island.