Competition between the krill fishery and penguins in the South Shetland Islands

Among the South Shetland Islands, the potential competition for krill (Euphausia superba) between the Japanese fishery and krill-eating breeding penguins was assessed. A low level of competition was apparent due to several factors. Spatial overlap between the main fishing and foraging areas was insignificant. Firstly, the large colonies of the dominant penguin (chinstrap penguins,Pygoscelis antarctica) occurred where sea ice disappears early in spring, and not necessarily where krill are abundant in summer, i.e. the area of krill fishery. Secondly, overlap between trawling depth and foraging dive depth of penguins was marginal, with the latter depth being shallower. Moreover, overlap in the size-frequency of krill caught by trawlers and those captured by penguins was not complete; the penguins took larger krill on average. Finally, the present small fishery is unlikely to impact upon local krill biomass in the region. Krill biomass was estimated to be 250–1500 × 10³ tonnes within the preferred fishing areas during summer. The present catch rate by the fishery (≤13 × 10³ tonnes/half-month period) is smaller by an order of magnitude, and the fishing area does not include the main foraging areas of breeding penguins.