batch_auto_20260713 202607131256465730 BOEM ESP geoESPIS ESPIS@boem.gov Bureau of Ocean Energy Management Estimation of Abundance and Demographic Rates of Pacific Walruses Using a Genetics-based Mark-Recapture Approach Marine Mammals Management U.S. Fish and Wildlife Service The U.S. Fish and Wildlife Service initiated a Pacific walrus genetic mark-recapture project in 2013 to estimate abundance, survival, and reproductive rates. We conducted research cruises in June of each year from 2013–2016 in the Bering and Chukchi Seas to sample juveniles and adult females, and this award partially funded the research cruise in 2017. We used a Horvitz-Thompson-type estimator to estimate the abundance of calves, juveniles, and adult females. We used age structure surveys to adjust this estimate for the estimated proportion of the population that were adult males. Addition of data from 2016 and 2017 did not substantially improve recapture rates. Thus, we only report preliminary results from 2013–2015. We estimated total population abundance as 283,213 with 95% credible interval 93,000 – 478,975. We are exploring alternative approaches such as integrated population models and close-kin mark-recapture to increase precision of parameter estimates. 250000 U.S. Department of the Interior, Bureau of Ocean Energy Management, Environmental Studies Program https://doi.org/10.13039/100012475 M16PG00034 10.67297/9A1D91 https://boem.gov/awardpages/100113