Foraging ecology and interactions with fisheries of wandering albatrosses (Diomedea exulans) breeding at South Georgia
Knowledge about the areas used by the foraging wandering albatross, Diomedea exulans, its prey and overlap with longline fisheries is important information not only for the conservation of this species but also for furthering our understanding of the ecology of its prey. We attached satellite-tracking devices and activity recorders to wandering albatrosses between May and July of 1999 and 2000 (years of differing food availability around South Georgia) in order to assess inter-annual variation in the main foraging areas, association with oceanographic features (i.e. fronts, bathymetry), diet and interactions with fisheries. The overall foraging patterns of the tracked birds were similar in 1999 and 2000, ranging between southern Brazil (28degreesS) and the Antarctic Peninsula (63degreesS) and between the waters off Tristan da Cunha (19degreesW) and the Patagonian Shelf and oceanic waters south of Cape Horn (68degreesW) in the South Atlantic. In 1999, wandering albatrosses spent most time in sub-Antarctic oceanic waters, their trip durations were significantly longer and they fed on fish and cephalopods (53 and 42% by mass, respectively). In contrast, in 2000, they spent more time in Antarctic waters, foraging trips were shorter and the diet was predominantly fish (84% by mass). Wandering albatrosses were associated with the sub-Antarctic Front (SAF; both years), Subtropical Front (STF; in 1999) and the Tropical Front (TF; in 2000) suggesting that this species exploits prey concentrated at oceanic fronts. Fisheries discards also seemed to provide a very good source of food. Several fish species that are targeted (e.g. Patagonian toothfish, Dissostichus eleginoides) or are available as offal/discards from commercial fisheries (e.g. the macrourids, Antimora rostrata and Macrourus holotrachys) were mainly associated with the South Georgia shelf and the Patagonian Shelf, respectively. Wandering albatross foraging areas overlapped with longline fisheries in three different regions: around South Georgia, at the Patagonian Shelf and in oceanic waters north of 40degreesS. Females commuted more frequently to the Patagonian Shelf and to oceanic areas where longline fisheries were operating. Males, on the other hand, spent more time on the shelf/shelf slope of South Georgia where they were more at risk from the local Patagonian toothfish fishery, particularly in 2000. These results emphasize that inter-annual variation in foraging preferences could lead to increased incidental mortality of this vulnerable species. Potential evidence for this is provided by a satellite-tracked wandering albatross (male; 1.8-day trip), whose diet contained a Patagonian toothfish head and a longline hook, and who spent extensive time in the water (44% of the time wet; 0.3 days of the trip) where a Patagonian toothfish longline fishing vessel was operating.