Foraging zones of the two sibling species of giant petrels in the Indian Ocean throughout the annual cycle: implication for their conservation

We studied the annual distribution, activity and breeding foraging trips of the sibling species of giant petrels, Northern Giant Petrel Macronectes halli and Southern Giant Petrel Macronectes giganteus from the  Crozet Islands (46°25'S; 51°51'E) where the 2 species breed sympatrically and Kerguelen Island (49°19'S; 69°15'E where Northern Giant petrels breed). Distribution and activity data were provided by GLS loggers (Global Location Sensing), and detail of breeding foraging trips were provided by ARGOS PTT. In order to assess differences in bycatch susceptibility, comparisons were made between species, sexes, stages (adult breeding, adult non breeding and juveniles) and sites. Activity patterns were investigated using GLMM and distribution ranges were determined using kernels analysis.



Overall, in adults, all stages remained close to nesting sites, during and outside the breeding season, while juveniles dispersed throughout the southern ocean. In adults, the intersexual differences were higher than interspecific ones, with females showing a greater distribution range than males in both species. Females also spent more time sitting on the water than males, particularly during wintering months. These results have important conservation implications, with males and females facing different kinds of threat in relation to their at-sea behavior. Adults, especially males, are more likely to be threatened by toothfish longline fisheries on shelf area of EEZs, and adult females as well as juveniles, are more likely to overlap with high sea longlining such as tuna fisheries.