Movements, at-sea distribution and behaviour of a tropical pelagic seabird: the wedge-tailed shearwater in the western Indian Ocean

This is the first study using geolocators (global location sensing, GLS) to track the movements of a pelagic tropical seabird. We used GLS to describe at-sea distribution and activity patterns of wedge-tailed shearwaters Puffinus pacificus breeding on Aride Island, Seychelles, in the late chick-rearing, non-breeding and pre-breeding periods. During late chick-rearing and pre-breeding periods, shearwaters foraged relatively close to the colony. In the non-breeding period, shearwaters; were found on a west-east gradient along the equator, between 5 degrees N and 10 degrees S. Some of the tracked individuals showed little dispersion, staying as close as 1000 km to Aride Island, while others travelled 3500 km to the Central Indian Ocean Basin. Individual core areas of activity showed little overlap. Overall, wedge-tailed shearwaters showed short-distance movements and exploited relatively unproductive oceanic waters. At-sea distribution largely matched that of yellowfin and skipjack tunas, emphasising the importance of the association with subsurface predators rather than associations with physical oceanographic features that enhance primary productivity. During the non-breeding period, the feeding activity of, shearwaters was mainly concentrated in the daylight period, when tunas also forage. A different behaviour, characterised by a much lower proportion of the night sitting on the sea surface, was recorded in the pre-laying exodus of 1 female to more productive waters, suggesting a different feeding strategy and/or targeting of different prey. Knowledge of the at-sea distribution of wedge-tailed shearwaters allows quantification of the overlap with industrial fisheries, which will be crucial to devise fisheries policies for the Indian Ocean with important implications for the conservation of this species.

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