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Application of airborne thermal imagery to surveys of Pacific walrus

Wildlife Society Bulletin

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Abstract

We conducted tests of airborne thermal imagery of Pacific walrus to determine if this technology can be used to detect walrus groups on sea ice and estimate the number of walruses present in each group. In April 2002 we collected thermal imagery of 37 walrus groups in the Bering Sea at spatial resolutions ranging from 1-4 m. We also collected high-resolution digital aerial photographs of the same groups. Walruses were considerably warmer than the background environment of ice, snow, and seawater and were easily detected in thermal imagery. We found a significant linear relation between walrus group size and the amount of heat measured by the thermal sensor at all 4 spatial resolutions tested. This relation can be used in a double-sampling framework to estimate total walrus numbers from a thermal survey of a sample of units within an area and photographs from a subsample of the thermally detected groups. Previous methods used in visual aerial surveys of Pacific walrus have sampled only a small percentage of available habitat, resulting in population estimates with low precision. Results of this study indicate that an aerial survey using a thermal sensor can cover as much as 4 times the area per hour of flight time with greater reliability than visual observation.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Application of airborne thermal imagery to surveys of Pacific walrus
Series title:
Wildlife Society Bulletin
Volume
34
Issue:
1
Year Published:
2006
Language:
English
Publisher:
U.S. Fish and Wildlife Service
Contributing office(s):
Alaska Biological Science Center
Description:
pp. 51-58
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Wildlife Society Bulletin
First page:
51
Last page:
58
Number of Pages:
8