Cephalopod predation by the king penguin Aptenodytes patagonicus from South Georgia

The king penguin Aptenodytes patagonicus is a sub-Antarctic species that feeds primarily on mesopelagic fish and cephalopods in the vicinity of the Antarctic Polar Front (APF). We examined the cephalopod prey of adult penguins at a breeding colony on South Georgia during 4 austral summers, 1990 to 1994. The most important prey (similar to 97 % by mass) of the king penguins was found, in a related study, to be mesopelagic fish, mainly myctophids. The penguins' cephalopod prey, which constituted the remaining 3%, was shown in this study to be dominated by the ommastrephid squid Martialia hyadesi, both in terms of numbers and biomass. Other squid species were typical of the South Georgia/Antarctic Polar Front (APF) area but only relatively small specimens were present and, apart from Gonatus antarcticus, the presence of flesh indicated that they were probably mostly caught close to the island. M. hyadesi generally fell in the same size range as M. hyadesi exploited by commercial fisheries in the South Atlantic. In the 1992/93 summer, when krill was abundant at South Georgia, the amount of squid consumed, especially M. hyadesi, was substantially less than in the other years. This coincided with a reduction in the amount of the myctophid Krefftichthys anderssoni, which is the major prey of M. hyadesi, in the penguin diet. The total consumption of cephalopods by the king penguin at South Georgia is estimated to be about 75 000 t yr(-1). Of this, some 3600 to 6000 t yr(-1) is estimated to be M. hyadesi. This might underestimate consumption if the penguins consume a greater proportion of squid in the winter, as they do in other sectors of the Southern Ocean.