Home-range overlap and site fidelity in the winter foraging movements of Antarctic fur seals
Benjamin Arthur

Authors

BT Arthur
Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia

MA Hindell
Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia

MN Bester
Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa

ME Goebel
NOAA South West Fisheries Science Centre, La Jolla, USA

ID Jonsen
Ocean Tracking Network, Department of Biology, Dalhousie University, Halifax, Canada

WC Oosthuizen
Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa

MD Sumner
Australian Antarctic Division, Channel Highway, Kingston, TAS 7050, Australia

PN Trathan
British Antarctic Survey, Cambridge, United Kingdom

M-A Lea
Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia

Abstract

The Antarctic fur seal (Arctocephalus gazella) is a numerous and key Southern Ocean predator yet little is understood regarding foraging site fidelity in this species. During the non-breeding austral winter, female Antarctic fur seals undertake long-distance migrations, which were studied at three circum-polar breeding colonies (Marion Island, South Georgia and the Antarctic Peninsula) in 2008-2011. During the latter part of the lactation period in March/April of each year, animals were equipped with miniaturised geolocation tags (GLS) to track at-sea movements. Since 2008, winter tracks of ~8 months duration have been collected for 139 adult females. State-space modeling was employed to identify regions of area-restricted search behaviour, indicating areas of large-scale foraging activity. Kernel-based home range analyses were undertaken to identify home range size and overlap to quantify site fidelity. This was done at three scales: within trip, between successive trips across a year, and between years for animals tracked over multiple winters (n=6); a rare data set in marine biotelemetry studies. The long-term variability (10 plus years) of key environmental parameters including sea-surface temperature, sea-surface height, chlorophyll- a concentration, as well as bathymetric features, were assessed and compared between areas of high and low home-range overlap. There was a higher degree of home-range overlap between years (64 ± 16%) than within years (49 ± 15%), whilst overlap within trips was relatively low (24 ± 3%). Initial results suggest a range of winter foraging areas in female Antarctic fur seals and strong site fidelity both within and between years. Such strong foraging site fidelity has a number of ecological, evolutionary and conservation implications for competition, net long-term energy gain, niche specialization and the ability of individuals to respond to environmental change.