Abstract:
Interspecific competition is an important structuring element in marine ecosystems,
especially in the Southern Ocean which offers few prey choices to comparatively large predator
populations. We present the first simultaneous observations of at-sea behaviour and attendance
patterns of 3 synchronously breeding, central place, krill foragers at Bouvetøya—a small, isolated,
sub-Antarctic island in the South Atlantic. Time depth recorders and satellite transmitters were
deployed during the austral summer of 2007/2008 on 47 lactating Antarctic fur seals Arctocephalus
gazella (AFS) rearing pups and on 20 macaroni Eudyptes chrysolophus (MAC) and 30
chinstrap Pygoscelis antarctica penguins (CHIN) rearing chicks. All 3 species showed a strong
preference for the west side of the island, and their foraging ranges overlapped markedly. Solar
elevation influenced the timing of departures from, and arrivals to, the island with markedly different
patterns between the seals and the penguins. Diving patterns also showed significant differences
among the 3 species, with the frequency of diving being higher at night for the AFS,
while both penguin species dove more frequently during the day. But a common, vertical diel
pattern occurred in all 3 species, with shallow diving occurring at night and deep diving during
the day, consistent with the vertical migration of krill. MACs targeted 2 depth layers for feeding,
including a deep prey layer at ~70 m, which was not exploited by AFSs and CHINs. The results
suggest that there is potential for competitive overlap among these 3 krill predators at Bouvetøya,
but that it is reduced via both spatial (horizontal and vertical) and temporal partitioning of foraging
areas.
