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    Penguins, fur seals, and fishing: prey requirements and potential competition in the South Shetland Islands, Antarctica

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    D.A. Croll and B.R. Tershy (USA)
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    Antarctic and sub-Antarctic seabirds, marine mammals, and human fisheries concentrate their foraging efforts on a single species, Antarctic krill (Euphausia superba). Because these predators may have a significant effect on krill abundance, we estimated the energy and prey requirements of Adelie (Pygoscelis adeliae), chinstrap (Pygoscelis antarctica), and gentoo (Pygoscelis papua) penguins and female Antarctic fur seals (Arctocephalus gazella) breeding on the South Shetland Islands, Antarctica and compared these estimates with catch statistics from the Antarctic krill fishery. Published data on field metabolic rate, population size, diet, prey energy content, and metabolic efficiency were used to estimate prey requirements of these breeding adult, land-based predators and their dependent offspring. Due to their large population size, chinstrap penguins were the most significant krill predators during the period examined, consuming an estimated 7.8 x 108 kg krill, followed by Adelie penguins (3.1 x 107 kg), gentoo penguins (1.2 x 107 kg), and Antarctic fur seals (3.6 x 106 kg). Total consumption of all land-based predators on the South Shetland Islands was estimated at 8.3 x 108 kg krill. The commercial krill fishery harvest m the South Shetland Island region (1.0 x 108 kg) was approximately 12% of this. Commercial harvest coincides seasonally and spatially with peak penguin and fur seal prey demands, and may affect prey availability to penguins and fur seals. This differs from the conclusions of Ichii et al. who asserted that the potential for competition between South Shetland predators and the commercial krill fishery is low.