MEPS 375:247-261 (2009)  -  DOI:

Deep into the ice: over-wintering and habitat selection in male Atlantic walruses

Carla Freitas1,2,*, Kit M. Kovacs1, Rolf A. Ims2, Michael A. Fedak3, Christian Lydersen1

1Norwegian Polar Institute, Polar Environmental Centre, 9296 Tromsø, Norway
2Institute of Biology, University of Tromsø, 9037 Tromsø, Norway
3NERC Sea Mammal Research Unit, Gatty Marine Laboratory, School of Biology, University of St. Andrews, St. Andrews, Fife KY16 8LB, UK

ABSTRACT: New technological developments in animal-borne satellite-tracking devices in combination with increased access to satellite-based environmental data are creating new possibilities for studying movement patterns and habitat selection by animals in remote, logistically challenging environments. In the present study, we report the first year-round data on movement patterns of walruses in the High Arctic, including at-sea positions. Using first-passage times (FPT) to study habitat use and quantifying habitat selection using mixed-effects Cox proportional hazards models, we dispelled the conventional perception that seasonal movement patterns of Atlantic walruses are simply a result of them following the retraction and expansion of annually formed sea ice. Walruses in this study (n = 17 males) actively moved into areas of high ice concentration (>90%) during winter; travelling far into the ice pack, as far as 600 km from ice-free water. Additionally, high inter-annual, seasonal site fidelity was documented. Seasonal differences in habitat use patterns were also observed. In summer, when walruses feed intensively, FPTs were affected by water depth and distance to the coast (R2 = 0.571), but these variables had no effect on walrus habitat use in winter. Sea ice concentration was the most important environmental condition during the winter season (R2 = 0.162), though there are clearly other factors influencing where individuals occur in winter that are currently unaccounted for in these analyses. The male walruses in this study did not do much benthic diving during winter, suggesting that they did not feed often during the time that they are known to breed. Instead, they remained in areas with high ice coverage, far from their coastal summering areas, spending much of their time hauled out or in surface waters.

KEY WORDS: Cox proportional hazards models · First-passage time · Odobenus rosmarus rosmarus · Random-effects models · Satellite telemetry · Site fidelity

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Cite this article as: Freitas C, Kovacs KM, Ims RA, Fedak MA, Lydersen C (2009) Deep into the ice: over-wintering and habitat selection in male Atlantic walruses. Mar Ecol Prog Ser 375:247-261.

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