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

Abstract

Antarctic and sub-Antarctic seabirds, marine mammals, and human fisheries concentrate their forag- ing eAorts on a single species, Antarctic krill (Euphausia superba). Because these predators may have a significant eAect on krill abundance, we estimated the energy and prey requirements of Adelie (Pygoscelis adeliae), chin- strap (Pygoscelis antarctica), and gentoo (Pygoscelis papua) penguins and female Antarctic fur seals (Arc- tocephalus gazella) breeding on the South Shetland Is- lands, 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 eAciency were used to estimate prey requirements of these breeding, adult, land-based predators and their dependent oAspring. Due to their large population size, chinstrap penguins were the most significant krill predators during the period examined, consuming an estimated 7.8 · 10 8 kg krill, followed by Adelie penguins (3.1 · 10 7 kg), gentoo penguins (1.2 · 10 7 kg), and Antarctic fur seals (3.6 · 10 6 kg). Total consumption of all land-based predators on the South Shetland Islands was estimated at 8.3 · 10 8 kg krill. The commercial krill fishery harvest in the South Shetland Island region (1.0 · 10 8 kg) was approximately 12% of this. Commercial harvest coin- cides seasonally and spatially with peak penguin and fur seal prey demands, and may aAect prey availability to penguins and fur seals. This diAers from the conclusions of Ichii et al. who asserted that the potential for com- petition between South Shetland predators and the commercial krill fishery is low.