Do inter-colony differences in Cape fur seal foraging behaviour reflect large-scale changes in the northern Benguela ecosystem?

  • M Skern-Mauritzen
  • SP Kirkman
  • E Olsen
  • A Bjørge
  • L Drapeau
  • MA Meÿer
  • J-P Roux
  • S Swanson
  • WH Oosthuizen

Abstract

The northern Benguela ecosystem adjoining Namibia has undergone considerable changes in recent decades, with reductions and northwards shifts of key prey species that have had severe implications for marine top predator populations. We investigated how such environmental variability may impact foraging behaviour of the Cape fur seal Arctocephalus pusillus pusillus, using satellite telemetry on animals in northern, central and southern Namibia. We expected that seal foraging behaviour would reflect a gradient of deteriorating feeding conditions from north to south. Results showed that foraging trips were shorter in the central region, where seals fed over the continental shelf, than in the north or south, where seals fed at the shelf edge. However, whereas seals in the north showed strong fidelity to the colony at which they were tagged and to persistent, clustered foraging areas, seals in the south showed weak fidelity both to the  colony at which they were tagged and to foraging areas, which were scattered and variable. Seals in the south also tended to migrate  northwards to other colonies while concurrently adapting their foraging behaviour to local conditions. Flexible use of foraging space and colonies of Cape fur seals during the three-year period (2002–2004) demonstrates that the species is adapted for variable environments over time and space.

Keywords: ecosystem shifts; foraging ecology; marine mammals; marine top predators; trophic interactions

African Journal of Marine Science 2009, 31(3): 399–408

Author Biographies

M Skern-Mauritzen
Institute of Marine Research, PO Box 1870, 5871 Bergen, Norway
SP Kirkman
Animal Demography Unit, Department of Zoology, University of Cape Town, Rondebosch 7701, South Africa; Marine and Coastal Management, Department of Environmental Affairs, Private Bag X2, Rogge Bay 8012, South Africa
E Olsen
Institute of Marine Research, PO Box 1870, 5871 Bergen, Norway
A Bjørge
Institute of Marine Research, PO Box 1870, 5871 Bergen, Norway
L Drapeau
Institut de Recherche pour le Développement, 213 Rue la Fayette, Paris, France
MA Meÿer
Marine and Coastal Management, Department of Environmental Affairs, Private Bag X2, Rogge Bay 8012, South Africa
J-P Roux
Lüderitz Marine Research, Ministry of Fisheries and Marine Resources, PO Box 394, Lüderitz, Namibia
S Swanson
Marine and Coastal Management, Department of Environmental Affairs, Private Bag X2, Rogge Bay 8012, South Africa; Current address: Ocean’s Research, Dias Museum, Private Bag X1, Mossel Bay 6500, South Africa
WH Oosthuizen
Marine and Coastal Management, Department of Environmental Affairs, Private Bag X2, Rogge Bay 8012, South Africa
Section
Articles

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