The Weddell seal population in Erebus Bay, Antarctica, represents one of the best-studied marine mammal populations in the world, providing an ideal test for the efficacy of satellite imagery to inform about seal abundance and population trends. Using high-resolution (0. 6m) satellite imagery, we compared counts from imagery to ground counts of adult Weddell seals and determined temporal trends in Erebus Bay during November 2004-2006 and 2009, and December 2007. Seals were counted from QuickBird-2 and WorldView-1 images, and these counts were compared with ground counts at overlapping locations within Erebus Bay during the same time. Counts were compared across years and within individual haul-out locations. We counted a total of 1,000 adult Weddell seals from five images across all years (for a total of 21 satellite-to-ground count comparisons), approximately 72% of the total counted on the ground at overlapping locations. We accurately detected an increase in abundance during 2004-2009. There was a strong, positive correlation (r=0. 98, df=3, P<0. 003) between ground counts and counts derived from the imagery. The correlation between counts at individual haul-out locations was also strong (r=0. 80, df=19, P>0. 001). Detection rates ranged from 30 to 88%. Overall, our results showed the utility of high-resolution imagery to provide an accurate way to detect the presence and variation in abundance of Weddell seals. Our methods may be applied to other species in polar regions, such as walruses or polar bears, particularly in areas where little is known about population status.
Bibliographical noteFunding Information:
Acknowledgments This work was funded by National Science Foundation grants OPP-0753663, OPP-0944411 and OPP-0635739. Satellite imagery data were copyright of DigitalGlobe, Inc. and provided through the Commercial Imagery Program by the National Geo-spatial-Intelligence Agency. We thank the United States Air Force, Raytheon Polar Services Company, and Petroleum Helicopters International for assistance with Weld logistics. B. Herried provided consultation for Wgures and S. Barber-Meyer, C. Southwell, and M. Cameron provided valuable insight into a previous draft of the manuscript.
Copyright 2011 Elsevier B.V., All rights reserved.
- Erebus Bay
- Leptonychotes weddellii
- Remote sensing
- Satellite imagery
- Weddell seal