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#           Regional walrus abundance estimate in the United States Chukchi Sea in autumn      

      June 6, 2022    

Human activities (e.g., shipping, tourism, oil, gas development) have increased in the Chukchi Sea because of declining sea ice. The declining sea ice itself and these activities may affect Pacific walrus (Odobenus rosmarus divergens) abundance; however, previous walrus abundance estimates have been notably imprecise. When sea ice is absent from the eastern Chukchi Sea, walruses in waters of the United States usually rest together onshore at a single Alaska coastal haulout, where they can be surveyed more easily than when they rest on dispersed offshore ice floes. We estimated the number of walruses on land (herd size) at this haulout from 13 unoccupied aircraft system (UAS) surveys flown within a 10-day period in each of 2018 and 2019. We estimated population size of walruses using the haulout over the course of the surveys by combining herd size data with data from satellite-linked transmitters that indicated whether tagged walruses were in or out of water during each survey. Our estimates of the population size of walruses using the haulout during each year's survey period were similar to each other and more precise than historical walrus abundance estimates: posterior means (95% credibility intervals) were 166,000 (133,000–201,000) for 2018 and 189,000 (135,000–251,000) for 2019. Auxiliary observations support using these estimates to represent the size of the population using the eastern Chukchi Sea in autumn during the surveyed years. Our study site was the only substantial Chukchi Sea coastal haulout in the United States during the survey periods and study-specific tracking data (consistent with known distribution and movement patterns) indicated tagged walruses remained in eastern Chukchi waters during the survey periods. In addition, the imagery, telemetry, and analytical methods developed for this study advance the prospect for precise range-wide walrus population size estimates.

## Citation Information

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#### Anthony Fischbach

##### Research Wildlife Biologist

Alaska Science Center

afischbach@usgs.gov

907-786-7145

#### Rebecca Taylor, Ph.D.

##### Research Statistician

Alaska Science Center

rebeccataylor@usgs.gov

907-786-7004

## Related Content

July 8, 2022

####                 Tracking Data for Pacific Walrus (Odobenus rosmarus divergens)              

Alaska Science Center

May 5, 2022

####                 Walrus Haulout Aerial Survey Data Near Point Lay Alaska, Autumn 2018 and 2019              

Alaska Science Center

January 13, 2022

####                 Behavior of Pacific Walruses (Odobenus rosmarus divergens) Hauled Out on Sea Ice During UAS Overflights, Eastern Chukchi Sea, 2015              

Alaska Science Center

#### Anthony Fischbach

##### Research Wildlife Biologist

Alaska Science Center

afischbach@usgs.gov

907-786-7145

#### Rebecca Taylor, Ph.D.

##### Research Statistician

Alaska Science Center

rebeccataylor@usgs.gov

907-786-7004

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####               Alaska Science Center          

4210 University DriveAnchorage, AK99508United States

(907) 786-7000

(907) 786-7020

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