Arctic | Mammals
Evaluation of satellite imagery for counting Pacific walrus carcasses at coastal haulouts Presenter: Anthony Fischbach , afischbach@usgs.gov, U.S. Geological Survey Alaska Science Center David Douglas , ddouglas@usgs.gov, U.S. Geological Survey Alaska Science Center Pacific walruses must rest out of water between foraging bouts. In the absence of sea ice, they rest on shore in dense aggregations at habitually used locations known as haulouts. When disturbed at coastal haulouts walruses may stampede. Some stampede events have resulted in the death of as many as one thousand individuals (typically calves) which is sufficient to impact population growth. Managers require an understanding of the frequency and magnitude of disturbance events at coastal haulouts, however, most are remote and difficult to access. Here we explore use of sub-meter resolution synthetic aperture radar (SAR) satellite imagery to detect and count walrus carcasses at two large coastal haulouts. One coastal haulout, in northwestern Alaska, was accessible to a ground survey team, and the other in northeastern Chukotka was not. We monitored haulout occupancy with C-band SAR imagery collected by the European Space Agency’s Sentinel-1 satellite (10-m resolution) as well as by the Canadian Radarsat-2 satellite (~1-meter imagery). That monitoring helped us target collections of sub-meter resolution X-band SAR imagery by the German Aerospace Agency’s TerraSAR-X satellite and the U.S. commercial Capella Space satellite constellation, prior to the formation of the haulout and shortly after it was abandoned for the season. Two observers independently examined satellite images to detect and digitized walrus carcasses using visual interpretation. We compared interpretations from satellite images between observers and, relative to the ground surveys at the Alaska study site. Here we report preliminary results and discus potentials for expanding these methods to monitor carcasses at Pacific walrus haulouts range wide.
Alaska Marine Science Symposium 2023 292
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