UNUSUAL BREEDING BY SEABIRDS AT MARION ISLAND DURING 1997/98

In 1997/98, breeding at subantarctic Marion Island was exceptionally good for five species of seabirds capable of foraging over wide areas and for a tern. The number of king penguin Aptenodytes patagonicus chicks surviving to the start of spring in 1997 was considerably more than previously recorded. Greater numbers of wandering Diomedea exulans and grey-headed Thalassarche chrysostoma albatrosses, northern giant petrels Macronectes halli and Kerguelen terns Sterna virgata bred than previously recorded, and more southern giant petrels M. giganteus did so than in any other year since 1994. For southern giant petrels, reproductive success was higher than in any other year, as was survival of chicks of northern giant petrels. Conversely, for two seabirds that feed close to the island, gentoo penguin Pygoscelis papua and Crozet shag Phalacrocorax [atriceps] melanogenis, 1997/98 was a particularly poor breeding season. Gentoo penguins initiated breeding later than usual and fledged few chicks. The number of Crozet shags that bred decreased; probably about 25% of the adult population did not breed. For two species with an intermediate foraging range that eat mainly crustaceans, macaroni Eudyptes chrysolophus and eastern rockhopper E. chrysocome filholi penguins, breeding was not noticeably different from normal except that chicks of rockhopper penguins fledged with a slightly heavier mass than in other years. However, for both these penguins, the mass of adults on arrival at colonies decreased substantially in the following (1998/99) breeding season. The unusual breeding by most of the seabirds coincided with the El Niño Southern Oscillation (ENSO) event of 1997/98. This synchrony contrasts with lagged responses to ENSO events of seabirds that breed farther south in the Southern Ocean. Continued monitoring of seabirds over well-separated sites in the Southern Ocean may elucidate how climatic perturbations operating at a global scale impact seabirds in the region.Afr. J. mar. Sci. 25: 453–46