Differences in foraging strategy and maternal behaviour between two sympatric fur seal species at the Crozet Islands

Abstract

Marine top-predators such as marine mammals forage in a heterogeneous environment according to their energetic requirements and to the variation in environmental characteristics. In this study, the behaviour of breeding females in 2 sympatric fur seal species, Antarctic fur seal Arctocephalus gazella and Subantarctic fur seal A. tropicalis, was investigated in relation to foraging effort. Foraging effort was hypothesised to be greater in Antarctic fur seal than in Subantarctic fur seal due to their shorter lactation period. Using satellite telemetry, time-depth recorders and satellite images of sea-surface temperature and chlorophyll a concentration, the foraging grounds, the at-sea activity budgets and the environmental features were determined for both species breeding on the Crozet Archipelago. Foraging cycle duration was similar for the 2 species, and the seals exhibited similar at-sea activity budgets. Only the proportion of time spent at sea was higher in Antarctic fur seals. Separate foraging areas were identified for the 2 species. Antarctic fur seal distribution was related to bathymetric features, while we did not find any direct relationship between chlorophyll a concentration and seal foraging areas. Our results suggest that Antarctic fur seals tend to respond to the higher needs of their pups by having a higher foraging efficiency and concentrating their foraging activity in the most productive areas.

Bathymetry and frontal system interactions influence seasonal foraging movements of lactating subantarctic fur seals from Marion Island

“…These at-sea trip durations correspond more closely with those from Amsterdam Island (Beauplet et al 2004), than with those from the neighbouring Îles Crozet (Bailleul et al 2005, Luque et al 2007 or the more distant, but also within the PFZ, Macquarie Island (Robinson et al 2002). This apparently inconsistent association between the latitudinal position of Marion Island and the duration of time spent at sea forms a central issue in the present study.…”

“…The present study confirms that subantarctic fur seal females at Marion Island undertake equally lengthy foraging trips, as has been shown for Amsterdam Island fur seals (Beauplet et al 2004). The Marion Island fur seals do not feed inshore and do not make overnight foraging trips, in contrast to fur seal behaviour during summer at the neighbouring Îles Crozet (Bailleul et al 2005, Luque et al 2007) and at Macquarie Island, which is located at a comparable latitude (Robinson et al 2002).…”

“…Some studies have focused on comparative foraging ecology of subantarctic and Antarctic fur seals A. gazella at 2 of the 3 island groups where they breed sympatrically, namely Îles Crozet (Bailleul et al 2005, Luque et al 2007) and Macquarie Island (Robinson et al 2002). Both these island systems are situated within the Polar Frontal Zone (PFZ), a diverse and heterogeneous oceanscape in the path of the Antarctic Circumpolar Current (ACC) bounded to the north by the Subantarctic Front (SAF) and to the south by the Antarctic Polar Front (APF) (Lutjeharms & Valentine 1984).…”

“…Both these island systems are situated within the Polar Frontal Zone (PFZ), a diverse and heterogeneous oceanscape in the path of the Antarctic Circumpolar Current (ACC) bounded to the north by the Subantarctic Front (SAF) and to the south by the Antarctic Polar Front (APF) (Lutjeharms & Valentine 1984). At both these localities, overnight foraging trips comprise a large proportion (~40 to 50%) of the total number of trips during summer, with the longer trips rarely exceeding 10 d or 100 km from the particular island (Robinson et al 2002, Bailleul et al 2005, Luque et al 2007). The position of Îles Crozet and Macquarie Island within the productive PFZ is hypothesised as one explanation for the predominance of short overnight foraging trips by those seals.…”

Oxygen stores and foraging behavior of two sympatric, planktivorous alcids

“…In marine ecosystems, some sympatric large-bodied animals (penguins and seals) possess differences in O 2 stores and segregate based on dive depth, with one species feeding on high density prey at depth and another on low density prey nearer the surface (Trivelpiece et al 1987, Mori & Boyd 2004. Other sympatric large-bodied species show similar dive abilities but segregate based on foraging locations (Trivelpiece et al 1987, Hull 1999 or timing of foraging activities (Bailleul et al 2005, Luque et al 2007). In contrast, the mechanisms underlying the partitioning of aquatic resources among sympatric populations of small seabirds remain unclear.…”