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Under-yearling and yearling southern elephant seal (Mirounga leonina) movements at Marion Island: bathymetric relationships

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Citation:
Tosh, C. , Bester, M. N. , Bornemann, H. , Burton, H. R. , Pistorius, P. A. , Plötz, J. , Ramdohr, S. , Stewart, B. and van den Hoff, J. (2007): Under-yearling and yearling southern elephant seal (Mirounga leonina) movements at Marion Island: bathymetric relationships , 17th Biennial Conference on the Biology of Marine Mammals, 29 November - 3 December 2007, Cape Town, South Africa. .
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Abstract:

The existence of elephant seals (Mirounga leonina) is energetically demanding. Finding patchily distributed food throughout the Southern Ocean varies between populations and individuals. Uniquely marked (Pistorius et al. 1999) underyearling (n=4) and yearling (n=11) southern elephant seals were instrumented with satellite transmitters from 2001 2006. Their movements were analysed and overlaid onto bathymetric (GEBCO) maps of the surrounding regions. Both age groups displayed an east to west path of travel with small variance in latitudinal travel and high variance in longitudinal travel. Eight of the 15 tracks were of 200 days or more, describing the movements of these seals from their first winter haul-out to the moult. The remaining 8 tracks describe a dispersal phase from east to west and terminate just before the animals were due to return to the island. Under-yearling and yearling elephant seals from Marion Island are shown to make two mid-winter trips. The seals travel exclusively along the South-West Indian Ridge in a westerly direction, directing their movements over areas of high bathymetric heterogeneity. All the under-yearling seals travelled to and from the island along the Andrew Bain fracture zone, seldom passing 25ºE. Yearling elephant seals showed varied dispersal strategies. Four yearlings displayed similar movements to under-yearlings. Five yearlings showed a tendency to move along the South-West Indian ridge up to 10ºE, most animals spent extended periods in the vicinity of the Meteor Rise and Sea- Mounts. One individual went as far as 5ºW, following the South-West Indian ridge until reaching the mid-Atlantic ridge. The strong relationships between bathymetric features and dispersal of juvenile elephant seals from Marion Island may be due to the interaction of varied bottom topography with overlying water bodies to generate areas of high turbulence resulting in high primary productivity.

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