Demography of the Pacific walrus (Odobenus rosmarus divergens): 1974-2006

Marine Mammal Science
By:  and 



Global climate change may fundamentally alter population dynamics of many species for which baseline population parameter estimates are imprecise or lacking. Historically, the Pacific walrus is thought to have been limited by harvest, but it may become limited by global warming-induced reductions in sea ice. Loss of sea ice, on which walruses rest between foraging bouts, may reduce access to food, thus lowering vital rates. Rigorous walrus survival rate estimates do not exist, and other population parameter estimates are out of date or have well-documented bias and imprecision. To provide useful population parameter estimates we developed a Bayesian, hidden process demographic model of walrus population dynamics from 1974 through 2006 that combined annual age-specific harvest estimates with five population size estimates, six standing age structure estimates, and two reproductive rate estimates. Median density independent natural survival was high for juveniles (0.97) and adults (0.99), and annual density dependent vital rates rose from 0.06 to 0.11 for reproduction, 0.31 to 0.59 for survival of neonatal calves, and 0.39 to 0.85 for survival of older calves, concomitant with a population decline. This integrated population model provides a baseline for estimating changing population dynamics resulting from changing harvests or sea ice.

Publication type Article
Publication Subtype Journal Article
Title Demography of the Pacific walrus (Odobenus rosmarus divergens): 1974-2006
Series title Marine Mammal Science
DOI 10.1111/mms.12156
Volume 31
Issue 1
Year Published 2015
Language English
Publisher Wiley
Contributing office(s) Alaska Science Center Biology MFEB
Description 24 p.
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Marine Mammal Science
First page 231
Last page 254
Online Only (Y/N) N
Additional Online Files (Y/N) N
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