Isolation by distance among California sea lion populations in Mexico: Redefining management stocks

M. González-Suárez, R. Flatz, D. Aurioles-Gamboa, P. W. Hedrick, Leah Gerber

Research output: Contribution to journalArticlepeer-review

46 Scopus citations


Understanding the spatial structure of a population is critical for effective assessment and management. However, direct observation of spatial dynamics is generally difficult, particularly for marine mammals. California sea lions (Zalophus californianus) are polygynous pinnipeds distributed along the Pacific coast of North America. The species' range has been subdivided into three management stocks based on differences in mitochondrial DNA, but to date no studies have considered nuclear genetic variation, and thus we lack a comprehensive understanding of gene flow patterns among sea lion colonies. In light of recent population declines in the Gulf of California, Mexico, it is important to understand spatial structure to determine if declining sea lion colonies are genetically isolated from others. To define population subdivision and identify sex biases in gene flow, we analysed a 355-bp sequence of the mitochondrial DNA control region and 10 polymorphic microsatellite loci from 355 tissue samples collected from six colonies distributed along Mexican waters. Using a novel approach to estimate sex biases in gene flow, we found that male sea lions disperse on average 6.75 times more frequently than females. Analyses of population subdivision strongly suggest a pattern of isolation by distance among colonies and challenge current stock definitions. Based on these results, we propose an alternative classification that identifies three Mexican management units: Upper Gulf of California, Southern Baja Peninsula, and Upper Pacific Coast of Baja. This revised classification should be considered in future assessment and management of California sea lion populations in Mexican waters.

Original languageEnglish (US)
Pages (from-to)1088-1099
Number of pages12
JournalMolecular ecology
Issue number6
StatePublished - Mar 2009


  • Gulf of California
  • Microsatellites
  • Mitochondrial DNA
  • Pinniped
  • Population structure
  • Sex-biased dispersal
  • Zalophus californianus

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Genetics


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