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MEPS 697:167-182 (2022)  -  DOI: https://doi.org/10.3354/meps14131

Estimating Pacific walrus abundance and survival with multievent mark-recapture models

William S. Beatty1,2,*, Patrick R. Lemons2, Jason P. Everett3, Cara J. Lewis3, Rebecca L. Taylor4, Robert J. Lynn2, Suresh A. Sethi5, Lori Quakenbush6, John J. Citta6, Michelle L. Kissling2,7, Natalia Kryukova8, John K. Wenburg3

1US Geological Survey, Upper Midwest Environmental Sciences Center, La Crosse, Wisconsin 54603, USA
2US Fish and Wildlife Service, Marine Mammals Management, Anchorage, Alaska 99503, USA
3US Fish and Wildlife Service, Conservation Genetics Laboratory, Anchorage, Alaska 99503, USA
4US Geological Survey, Alaska Science Center, Anchorage, Alaska 99508, USA
5US Geological Survey, New York Cooperative Fish and Wildlife Research Unit, Ithaca, New York 14853, USA
6Alaska Department of Fish and Game, Marine Mammal Program, Fairbanks, Alaska 99701, USA
7University of Montana, College of Forestry and Conservation, Missoula, Montana 59812, USA
8Kamchatka Branch of the Pacific Geographical Institute of Far Eastern Branch of Russian Academy of Sciences, 683000 Petropavlovsk-Kamchatsky, Russia
*Corresponding author:

ABSTRACT: Arctic marine ecosystems are undergoing rapid physical and biological change associated with climate warming and loss of sea ice. Sea ice loss will impact many species through altered spatial and temporal availability of resources. In the Bering and Chukchi Seas, the Pacific walrus Odobenus rosmarus divergens is one species that could be impacted by rapid environmental change, and thus, population assessments are needed to monitor changes in the status of this ecologically and culturally important marine mammal. We conducted a 5 yr genetic mark-recapture study to estimate demographic parameters for the Pacific walrus. We developed a Bayesian multievent mark-recapture model to estimate walrus survival and abundance while accounting for age misclassification. We estimated the probability of juvenile annual survival as 0.63 (95% credible interval [CrI]: 0.39-0.87) and adult female annual survival as 0.90 (95% CrI: 0.74-1.00). We estimated total abundance as 257 193 (95% CrI: 171 138-366 366). We provide the first estimate of total Pacific walrus abundance since an aerial survey in 2006, which generated a substantially less precise total population size estimate (129 000; 95% CI: 55 000-507 000). The emerging ecosystem state in the northern Bering and Chukchi Seas will likely result in a decline in Pacific walrus abundance, but there is substantial uncertainty regarding the magnitude of the anticipated decline. Our demographic estimates provide critical information to evaluate future population trends of this subsistence resource vital to communities that border the Bering and Chukchi Seas in the USA and Russia.


KEY WORDS: State misclassification · Horvitz-Thompson estimator · Age structure · Ratio estimator · Population monitoring


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Cite this article as: Beatty WS, Lemons PR, Everett JP, Lewis CJ and others (2022) Estimating Pacific walrus abundance and survival with multievent mark-recapture models. Mar Ecol Prog Ser 697:167-182. https://doi.org/10.3354/meps14131

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Published in MEPS Vol. 697. Online publication date: September 22, 2022
Print ISSN: 0171-8630; Online ISSN: 1616-1599
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