# Evaluation of Satellite Imagery for Monitoring Pacific Walruses at a Large Coastal Haulout
## 5 Conclusions  
Both optical and radar satellite imagery with resolutions \(\leq\) 10 m were useful in detecting the presence, areal size, and geographic position of walrus aggregations at a terrestrial haulout near Point Lay, Alaska. Results of this study suggest that satellite reconnaissance could expand haulout monitoring tools in a cost-effective manner relative to on-site options. Satellite imagery clearly revealed large walrus aggregations and allowed for quantification of the area occupied by those aggregations. Although large aggregations were evident in satellite imagery at the Point Lay study site, further research is needed to evaluate the capability of satellite imagery to distinguish walrus aggregations across the Pacific walrus range, including sites with more complex beach substrates and local topography. Estimating the actual number of walruses present at a haulout might be possible using very high-resolution satellite imagery, but only after calibration studies with simultaneously collected aerial imagery are successful.  
The following is available online at [[https://www.mdpi.com/article/10.3390/rs13214266/s1](https://www.mdpi.com/article/10.3390/rs13214266/s1)]([https://www.mdpi.com/article/10.3390/rs13214266/s1](https://www.mdpi.com/article/10.3390/rs13214266/s1)), Table S1: Tabulation of satellite images matched to within 24 h of UAS survey.  
Conceptualization, A.S.F.; methodology, A.S.F. and D.C.D.; validation, A.S.F. and D.C.D.; formal analysis, A.S.F. and D.C.D.; investigation, A.S.F. and D.C.D.; data curation, A.S.F.; writing--original draft preparation, A.S.F.; writing--review and editing, A.S.F. and D.C.D.; visualization, A.S.F.; funding acquisition, D.C.D. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the U.S. Geological Survey.  
The study was conducted according to the fundamental science practices of the USGS and received bureau approval (information product documentation system number IP-131033 on 13 September 2021).  
This study was conducted with informed consent of the Eskimo Walrus Commission, an Alaska Native co-management group that represents Alaskan coastal communities that rely on walruses.  
All data derived and summarized by this study are available online. Fischbach, A.S., Douglas, D.C., Monette, C.J. 2020, Walrus haulout outlines apparent from satellite imagery near Point Lay Alaska, autumn 2018, 2019, and 2020: U.S. Geological Survey data release, [[https://doi.org/10.5066/P9S2](https://doi.org/10.5066/P9S2) UL7N]([https://doi.org/10.5066/P9S2](https://doi.org/10.5066/P9S2) UL7N) (accessed on 20 October 2021).  
We are grateful to the Eskimo Walrus Commission for consulting on the study design. [PERSON] served at the third visual interpreter and provided insightful adjustments to optical imagery visualization as well as technical reviews of manuscript drafts. [PERSON] and [PERSON] provided guidance on use of Google Earth Engine for access to Landsat and Sentinel data. [PERSON] provided guidance on TeraSAR-X imagery collection. [PERSON] provided guidance on PlanetLabs PlanetScope imagery. [PERSON], [PERSON], [PERSON], and [PERSON] reviewed drafts of the manuscript. [PERSON] of the ANUVA GmbH landscape planning firm facilitated acquisition of the TerraSAR-X imagery. Observations of walrus occurrence along the Chukchi Sea coast of Alaska were provided through the community of Point Lay by [PERSON] and [PERSON], and through NOAA's Aerial Surveys of Arctic Marine Mammals program. The European Space Agency and the German Aerospace Agency (DLR) kindly granted access to TerraSAR-X imagery archive and the DLR granted acquisition of new imagery for our science application. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.  
The authors declare no conflict of interest.