Abstract
Detailed knowledge of habitat use by marine megafauna is critical to understand their ecological roles and for the adequate management of marine resources. Antarctic fur seals (Arctocephalus gazella) inhabiting the Atlantic sector of the Southern Ocean prey largely on Antarctic krill (Euphausia superba) and play a central role in managing the krill fishery. Here, we assessed the demographic structure of three post-mating, early moult male haul-outs in the South Shetland Islands in early March and calculated the relative contribution of juveniles (1–4 years old) and sub-adult males (5–6 years) to the population remaining in maritime Antarctica after the breeding season. We also satellite tagged 11 juvenile males and four sub-adult males to analyze their movements and develop a species distribution model including both age classes. Our results highlighted the dominance of young individuals in the male population, revealed that they do not behave as central place foragers and identified key environmental drivers that affected their distribution at-sea throughout winter. Predicted potential foraging habitat overlapped highly with the known distribution of Antarctic krill, and identified the waters off the western Antarctic Peninsula and the Scotia Sea as the core of the distribution area of juvenile and sub-adult male Antarctic fur seals in winter. This pattern is similar to that of adult males but totally different from that of adult females, as the latter overwinter in areas at latitude 45–55° S. This segregation has implications for the ecology and management of the krill fishery.
Highlights
Polar marine ecosystems are unique because of their extremely high degree of seasonality, low temperatures, strong oceanic currents and extensive seasonal sea ice c over[1,2]
Antarctic fur seals are highly sexually d imorphic[26,27,28,29,30] and differences between sexes in winter habitat use could be related to differences in body mass, which in turn is a major determinant of their thermoregulatory skills and diving p erformance[31,32]
Using visual surveys and satellite telemetry we have assessed the demographic structure at haul-outs after the breeding season and analysed the habitat use of juvenile and sub-adult males present in maritime Antarctica in winter
Summary
Polar marine ecosystems are unique because of their extremely high degree of seasonality, low temperatures, strong oceanic currents and extensive seasonal sea ice c over[1,2]. Crabeater seals (Lobodon carcinophaga) and Antarctic fur seals (Arctocephalus gazella) remain in large numbers during winter in maritime Antarctica (i.e. the part of the Southern Ocean closer to the Antarctic continent and limited to the sea ice)[6,8,9,10,11]. Satellite tracking and stable isotope analysis demonstrated that the winter at-sea habitats of adult female Antarctic fur seals breeding both close to the Antarctic Polar Front and in the South Shetland Islands are usually located at latitude 45–55° S13–21. Ship surveys have identified sea ice concentration as one of the major determinants of male Antarctic fur seal distribution off the South Shetland Islands and the Bransfield strait in winter[6]. Juvenile and sub-adult males are the age classes with the highest krill consumption of the overall population[41] and are of particular interest for the management of the krill fishery
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