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Demography of the Pacific walrus (Odobenus rosmarus divergens) in a changing Arctic

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Full Publication: https://doi.org/10.1111/mms.12434

Product Type: Journal Article
Year: 2017

Authors: Taylor, R. L., M. S. Udevitz, C. V. Jay, J. J. Citta, L. T. Quakenbush, P. R. Lemons, and J. A. Snyder

Suggested Citation:
Taylor, R. L., M. S. Udevitz, C. V. Jay, J. J. Citta, L. T. Quakenbush, P. R. Lemons, and J. A. Snyder. 2017. Demography of the Pacific walrus (Odobenus rosmarus divergens) in a changing Arctic. Marine Mammal Science 34(1):54-86. doi:10.1111/mms.12434

Abstract


The Pacific walrus (Odobenus rosmarus divergens) is a candidate to be listed as an endangered species under United States law, in part, because of climate change-related concerns. While the population was known to be declining in the 1980s and 1990s, its recent status has not been determined. We developed Bayesian models of walrus population dynamics to assess the population by synthesizing information on population sizes, age structures, reproductive rates, and harvests for 1974–2015. Candidate models allowed for temporal variation in some or all vital rates, as well as density dependence or density independence in reproduction and calf survival. All selected models indicated that the population underwent a multidecade decline, which began moderating in the 1990s, and that annual reproductive rate and natural calf survival rates rose over time in a density-dependent manner. However, selected models were equivocal regarding whether the natural juvenile survival rate was constant or decreasing over time. Depending on whether juvenile survival decreased after 1998, the population growth rate either increased during 1999–2015 or stabilized at a lesser level of decline than seen in the 1980s. The probability that the population was still declining in 2015 ranged from 45% to 87%.

Keywords: Climate change, Pacific walrus, population dynamics

Annotation


The Pacific walrus (Odobenus rosmarus divergens) is a candidate to be listed as an endangered species under United States law, in part, because of climate change-related concerns. This study describes a population that underwent a multidecade decline, but also one in which the severity of the decline likely lessened over time. Continued study and monitoring is needed to examine juvenile survival rates and generate better estimates of population abundance. This information is important for effective management and to respond to human activities that may impact walrus populations.