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Open-File Report 2015-1119

National Park Service, Southeast Alaska Inventory and Monitoring Network

Monitoring Population Status of Sea Otters (Enhydra lutris) in Glacier Bay National Park and Preserve, Alaska—Options and Considerations

By G.G. Esslinger, D. Esler, S. Howlin, and L.A. Starcevich

Thumbnail of and link to report PDF (1.8 MB)Abstract

After many decades of absence from southeast Alaska, sea otters (Enhydra lutris) are recolonizing parts of their former range, including Glacier Bay, Alaska. Sea otters are well known for structuring nearshore ecosystems and causing community-level changes such as increases in kelp abundance and changes in the size and number of other consumers. Monitoring population status of sea otters in Glacier Bay will help park researchers and managers understand and interpret sea otter-induced ecosystem changes relative to other sources of variation, including potential human-induced impacts such as ocean acidification, vessel disturbance, and oil spills. This report was prepared for the National Park Service (NPS), Southeast Alaska Inventory and Monitoring Network following a request for evaluation of options for monitoring sea otter population status in Glacier Bay National Park and Preserve. To meet this request, we provide a detailed consideration of the primary method of assessment of abundance and distribution, aerial surveys, including analyses of power to detect interannual trends and designs to reduce variation around annual abundance estimates. We also describe two alternate techniques for evaluating sea otter population status—(1) quantifying sea otter diets and energy intake rates, and (2) detecting change in ages at death. In addition, we provide a brief section on directed research to identify studies that would further our understanding of sea otter population dynamics and effects on the Glacier Bay ecosystem, and provide context for interpreting results of monitoring activities.

First posted July 1, 2015

For additional information, contact:
Director, Alaska Science Center
U.S. Geological Survey
4210 University Dr
Anchorage, Alaska 99508-4560
http://alaska.usgs.gov

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Suggested citation:

Esslinger, G.G., Esler, D., Howlin, S., and Starcevich, L.A., 2015, Monitoring population status of sea otters (Enhydra lutris) in Glacier Bay National Park and Preserve, Alaska—Options and considerations: U.S. Geological Survey Open-File Report 2015-1119, 42 p., https://dx.doi.org/10.3133/ofr20151119.

ISSN 2331-1258 (online)



Contents

Abstract

Introduction

Chapter 1. Estimating Sea Otter Abundance and Distribution Using Aerial Surveys

Chapter 2. Estimating Sea Otter Diets and Energy Intake Rates

Chapter 3. Detecting Change in Population Status by Monitoring Ages at Death

Directed Research

Synthesis

Acknowledgments

References Cited

Appendix A. Simulation Plots


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