Relative fisheries overlap of nonbreeding wandering albatrosses may explain colony-specific population trajectories at South Georgia

Bycatch in fisheries is one of the most serious threats to pelagic seabirds and is the cause of major population declines. Mitigation measures can reduce bycatch to negligible levels, but many fisheries fail to apply best practice and seabird mortality remains high. Seabirds often segregate at sea according to sex and life-history stage, and bycatch risk can vary accordingly. Few studies have tested whether spatial segregation among colonies in foraging areas affects bycatch risk. We tracked non-breeding wandering albatrosses Diomedea exulans from Bird Island and neighbouring Prion Island, South Georgia to investigate whether differences in at-sea distributions and overlap with fisheries might explain the contrasting population trends. Tracked individuals were of known status (immature or non-breeding adult) at Bird Island, and were mostly older immatures and potentially a few non-breeding adults at Prion Island. There was marked spatial segregation between age classes at Bird Island but the pattern was more complex between breeding sites. The differences in overlap with fisheries were more clear-cut; highest in non-breeding adults from Bird Island and lowest in birds from Prion Island. Overlap was highest with Chinese, South Korean and Taiwanese squid jiggers, Taiwanese pelagic longliners, and Argentinian and Spanish trawlers. Greater overlap with fisheries appears to be contributing to the faster rate of population decline at Bird Island than at Prion Island. By improving our knowledge of the spatio-temporal overlap of seabirds with fisheries, management initiatives can be directed at the fleets that represent the greatest threats to these iconic and threatened seabirds.