Exploitation of mesoscale oceanographic features by grey-headed albatross Thalassarche chrysostoma in the southern Indian Ocean

Breeding grey-headed albatross Thalassarche chrysostoma, tracked from Mario n Island (Prince Edward Islands) during November-December 1997 and January- February 1998, showed a strong association with mesoscale oceanographic fea tures, as identified by sea surface height anomalies, in the southern India n Ocean. During incubation, most birds foraged to the north of the island, at the edges of anomalies created by the Agulhas Return Current in the Subt ropical Convergence and the Subantarctic zones. In contrast, during chick-r earing all tracked birds foraged to the southwest of the island, at the edg es of anomalies along the South-West Indian Ridge. Previous work in this ar ea has shown that these anomalies are in fact eddies that are created as th e Antarctic Circumpolar Current crosses the South-West Indian Ridge. Diet s amples taken during the chick-rearing period showed a predominance of fresh specimens of the predatory fish Magnisudis prionosa and the squid Martiali a hyadesi. Myctophid fish and amphipods Themisto gaudichaudii, both known p rey of M. hyadesi, were also well represented in our samples. Diet samples taken from tracked birds showed birds feeding at edges of positive anomalie s returning with fresh specimens of M. prionosa and M. hyadesi. Predatory f ish and squid are thus presumably concentrated at these features. Eddies fo rmed at the South-West Indian Ridge have also been shown to drift closer to Marion Island, within the foraging range of penguins and seals breeding on Marion Island. We therefore suggest that these mesoscale oceanographic fea tures may be an important component of the 'life-support' system enabling g lobally significant populations of seabirds and seals to breed at the Princ e Edward Islands.