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Testing the nutritional-limitation, predator-avoidance, and storm-avoidance hypotheses for restricted sea otter habitat use in the Aleutian Islands, Alaska

  • Behavioral ecology - Original research
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Abstract

Sea otters (Enhydra lutris) inhabiting the Aleutian Islands have stabilized at low abundance levels following a decline and currently exhibit restricted habitat-utilization patterns. Possible explanations for restricted habitat use by sea otters can be classified into two fundamentally different processes, bottom-up and top-down forcing. Bottom-up hypotheses argue that changes in the availability or nutritional quality of prey resources have led to the selective use of habitats that support the highest quality prey. In contrast, top-down hypotheses argue that increases in predation pressure from killer whales have led to the selective use of habitats that provide the most effective refuge from killer whale predation. A third hypothesis suggests that current restricted habitat use is based on a need for protection from storms. We tested all three hypotheses for restricted habitat use by comparing currently used and historically used sea otter foraging locations for: (1) prey availability and quality, (2) structural habitat complexity, and (3) exposure to prevailing storms. Our findings suggest that current use is based on physical habitat complexity and not on prey availability, prey quality, or protection from storms, providing further evidence for killer whale predation as a cause for restricted sea otter habitat use in the Aleutian Islands.

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Acknowledgments

We would like to thank J. A. Estes for valuable comments and logistical support during this study. Contributions from D. M. Thomas, B. P. Kelly, and M. J. Wooller contributed greatly to earlier drafts of this manuscript. Special thanks to T. Efird, M. Stewart, S. Beaudreault, and J. P. Smelter for their assistance in the field. This research was primarily funded by the National Science Foundation (to B. K., award no. 0647635). Other financial support (to N. S.) was provided by the Robert Byrd Research Award, the Frances and Alfred Baker Memorial Scholarship in Marine Biology, and the Ken Turner Memorial Research Grant. This work would not have been possible without the support of the Alaska Maritime Wildlife Refuge, the R/V Tiglax, and US Fish and Wildlife Service staff at the Adak field office. All work reported in this paper was done in compliance with US law. Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the US government.

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Authors and Affiliations

  1. School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, 245 O’Neill Building, Fairbanks, AK, 99775, USA

    Nathan L. Stewart

  2. School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, 217 O’Neill, P.O. Box 757220, Fairbanks, AK, 99775, USA

    Brenda Konar

  3. US Geological Survey Western Ecological Research Center, Long Marine Laboratory, 100 Shaffer Road, Santa Cruz, CA, 95060, USA

    M. Tim Tinker

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  1. Nathan L. Stewart
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Correspondence to Brenda Konar.

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Communicated by Helene Marsh.

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Stewart, N.L., Konar, B. & Tinker, M.T. Testing the nutritional-limitation, predator-avoidance, and storm-avoidance hypotheses for restricted sea otter habitat use in the Aleutian Islands, Alaska. Oecologia 177, 645–655 (2015). https://doi.org/10.1007/s00442-014-3149-6

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  • DOI: https://doi.org/10.1007/s00442-014-3149-6

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