Population and Breeding of the Gentoo PenguinPygoscelis Papuaat Marion Island, 1994/95 – 2002/03

Abstract

The numbers of gentoo penguins Pygoscelis papua breeding at subantarctic Marion Island fell by 40% from 1994/95 to 2002/03, from 1 352 pairs to 806 pairs. Apart from a slight increase in 1998/99, there was a steady decrease in numbers breeding between 1995/96 and 2000/01, when the population stabilized. There is indication that in some years not all breeders nested and that some birds relocated to another colony after disturbance. From first clutches, pairs on average fledged between 0.01 chicks in 1997/98 and 0.58 chicks in 2002/03 (mean 0.38 ± 0.21). In 1994/95, replacement clutches increased the overall production of fledged chicks by 11%. Based on demographic parameters measured at other localities, the production of chicks at Marion Island was inadequate to maintain the population during the period 1995/96 -2000/01. Consistency in trends in breeding success at five colonies suggests that factors operating at a mesoscale, rather than those specific to particular colonies, often influenced breeding success. Laying was later than normal in 1997/98, when there was almost total breeding failure with large losses of eggs and small chicks to returning Subantarctic skuas Catharacta antarctica. Future research on this Near Threatened species at Marion Island must take full account of its susceptibility to human disturbance.

Conservation and management

“…The increase in sea-surface temperature may be related to a southerly shift in the mean position of the Sub-Antarctic Front, with the resultant advection of zooplankton and micronekton to the islands benefiting pelagic predators, but creating unfavourable feeding conditions for inshore feeders (Pakhomov & Chown 2003). Decreased food availability as a result of climate change has been implicated in the decline of three inshore-foraging species at the Prince Edward Islands: the Gentoo Penguin, Rockhopper Penguin E. chrysocome and Crozet Shag (Crawford et al 2003a(Crawford et al , 2003b(Crawford et al , 2004. Climatic perturbations on a global scale may also influence breeding by seabirds, as evidenced by a marked difference in the breeding success of inshore and offshore foragers in 1997/1998, a season coinciding with a major El Niño Southern Oscillation event (Crawford et al 2003c(Crawford et al , 2004.…”

“…Crawford, personal communication). Declines in some populations of Gentoo Penguins (Crawford et al 2003a) and Southern Giant Petrels on Marion Island have been associated with previous intrusive research programmes which were consequently discontinued. Removal of cats from Marion Island resulted in the accidental mortality of some seabirds but had no negative effects on population levels (Bloomer & Bester 1992;Bester et al 2002).…”

The Prince Edward Islands: Land-Sea Interactions in a Changing Ecosystem

“…Adult and subadult male Antarctic fur seals kill King Penguins Aptenodytes patagonicus and, to a lesser extent, Macaroni Penguins Eudyptes chrysolophus, mainly during August to October at Goodhope Bay, Marion Island (Hofmeyr & Bester 1993;Mammal Research Institute, unpublished data). It is possible that the decline in the small King Penguin colony at Goodhope Bay (Van Heezik et al 1995;Crawford et al 2003a) is due to seal predation.…”

“…At least King Penguins were exploited historically, but they have not been hunted since the 1930s , and the numbers taken were such that current populations probably show little if any impact of past exploitation (Crawford et al 2003a). Current populations are summarised in Table 6.2.…”

“…They are important in transporting penguin material away from the immediate coastal zone (Hunter 1995), and the islands support 11% of the world population (Crawford & Cooper 2003). Kelp Gulls and terns breed at scattered localities along the coast and inland, mainly along the more sheltered eastern coasts (Crawford et al 2003a;Ryan et al 2003a).…”