A noninvasive demographic assessment of sea lions based on stage-specific abundances

Jeffrey Wielgus, Manuela Gonzalez-Suarez, David Aurioles-Gamboa, Leah Gerber

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


A pressing need exists to develop new approaches for obtaining information on demographic rates without causing further threats to imperiled animal populations. In this paper, we illustrate and apply a data-fitting technique based on quadratic programming that uses stage-specific abundance data to estimate demographic rates and asymptotic population growth rates (λ). We used data from seven breeding colonies of California sea lions (Zalophus califomianus) in the Gulf of California, Mexico. Estimates of λ were similar to those from previous studies relying on a diffusion approximation using trends in total abundance. On average, predicted abundances were within 24% of the observed value for the inverse estimation method and within 29% of the observed value for the diffusion approximation. Our results suggest that three of the seven populations are declining (λ < 1), but as many as six may be at risk. Elasticity and sensitivity analyses suggest that population management in most sites should focus on the protection of adults, whose survival generally contributes the most to X. The quadratic programming approach is a promising noninvasive technique for estimating demographic rates and assessing the viability of populations of imperiled species.

Original languageEnglish (US)
Pages (from-to)1287-1296
Number of pages10
JournalEcological Applications
Issue number5
StatePublished - Jul 2008


  • Abundance
  • California sea lion
  • Demography
  • El Nino
  • Gulf of California
  • Inverse estimation
  • Marine mammals
  • Noninvasive techniques
  • Population viability analysis
  • Quadratic programming
  • Zalophus californianus

ASJC Scopus subject areas

  • Ecology


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