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

Abstract

Sixteen lactating subantarctic fur seals Arctocephalus tropicalis were satellite-tracked during the winter of 2006 (n = 6), summer of 2006/07 (n = 6) and autumn/winter (n = 4) of 2007, from Marion Island, Southern Ocean. Despite varied individual movement patterns, a favoured foraging area lay to the northeast of the island. In contrast to findings for populations at similar latitudes, seals from Marion Island did not undertake short overnight foraging trips, but trips consistently went beyond 300 km from the island. This aligns with the at-sea duration of lactating seals' foraging trips from temperate Amsterdam Island, but differs from subantarctic Crozet and Macquarie islands. Time spent at sea, maximum distances travelled and movement variation of tracks from the island varied seasonally. Faecal analysis suggests the diet comprised primarily myctophid fish with limited seasonal variation. Well-defined areas of restricted movement coincided with significant bathymetric features to the west/northwest of the Crozet Plateau, with the Del Caño Rise clearly being important. Positive and negative sea-surface height anomalies (compared to the mean) appeared to be preferred by most seals across seasons. Higher summer sea-surface temperatures correlated with the movements of some seals. Higher chlorophyll a concentrations dictated transit and foraging areas during summer. Bathymetrically influenced oceanographic variables likely explain these preferred long-distance eastward movements. The Îles Crozet and Marion Island subantarctic fur seals differ in their foraging ecology despite being neighbours. Conversely, the subantarctic fur seal populations from the distant Amsterdam and Marion islands appear to be similarly influenced by such environmental factors.

Movement and diving of killer whales ( Orcinus orca ) at a Southern Ocean archipelago

“…Seals and seabirds forage in diverse areas, often far from the PEIs, where they target frontal and bathymetric features at which their crustacean, fish and cephalopod prey are presumably concentrated (de Bruyn et al, 2009;Nel et al, 2001;Tosh et al, 2012). The shelf between the islands is somewhat enriched by topographic trapping of vertically migrating zooplankton and dense phytoplankton blooms (Perissinotto and Mcquaid, 1992) but the broad distribution pattern among seals and seabirds, however, reflects that macrozooplankton biomass over the inter-island shelf may be 3-8 times lower than in the offshore region.…”

Prevalence of allosuckling behaviour in Subantarctic fur seal pups

“…We used focal, low-density rookeries at Van den Boogaard (VdB) and Rockhopper Bay (RhB) to study at-sea movements and attendance cycles for another study (de Bruyn et al, 2009), at which time an opportunistic sustained allonursing/ milkstealing observation arose. These were augmented by opportunistic behavioural observations at Cape Davis (CD) (medium-density) and Mixed Pickle (MP) (highdensity) rookeries.…”

“…Additionally, the deployment of satellite linked tracking devices on several randomly selected healthy lactating females at the VdB or RhB colonies for a different study (see de Bruyn et al, 2009, for deployment and tracking analyses details) resulted in the fortuitous discovery of a sustained case of allosuckling.…”

The Marine Ecosystem of the Sub-Antarctic, Prince Edward Islands

“…Recent investigations have demonstrated conclusively that an extensive eddy train extends eastwards from the South-West Indian Ridge into the Prince Edward Island vicinity Durgadoo et al, 2010Durgadoo et al, , 2011. These eddies have a noticeable biological influence (Pakhomov et al, 2000;Bernard et al 2007; by transporting physical and biological characteristics typical of the Antarctic northwards into the island vicinity (Figure 4) thus the possibility of providing an important foraging grounds for grey-headed albatrosses (Nel et al, 2001) and elephant seals (de Bruyn et al, 2009). Based on the geographic distribution of these eddies it has been surmised that their origin is as a direct result of the interaction of the ACC with the South-West Indian Ridge and in particular the series of fractures; notably the Du Toit, Andrew Bain, Marion and Prince Edward, which intersect this ridge between 25° -35°E and 45° -55°S and divide the SouthWest Indian Ridge into two almost equally extensive sections (Sclater et al, 2005).…”