Population Genetics of Steelhead in the

Navarro River Drainage 

For more information contact: jfcordes@ucdavis.edu  

Collaborators

    This genetic study is part of a larger project conducted by Dr. Michael Johnson's group at UC Davis' John Muir Institute of the Environment (JMIE) investigating the ecology and life history of steelhead in the Navarro River watershed. Funding is provided by CALTRANS. 

Background and Significance of Study   

   Steelhead, the anadromous form of rainbow trout Oncorhynchus mykiss, once ranged along the eastern Pacific coast from Alaska to Baja California.  Currently all three recognized forms of steelhead in California are considered to be in decline (winter steelhead) or qualify as threatened (summer steelhead) or endangered (southern steelhead) under the federal Endangered Species Act (Moyle et al. 1995).  Significant threats to the continued survival of genetically distinct California steelhead populations include habitat degradation and loss, competition with and predation by introduced fishes, and introgressive hybridization with hatchery rainbow trout (Williams et al. 1989, Moyle et al. 1995).  

  The purpose of this study is to develop a database characterizing the genetic variation within and between steelhead populations utilizing different streams within the Navarro River drainage on the northern California coast. In addition to characterizing population structure within the basin, this data would have a number of other uses. First, baseline data could be used to monitor the genetic health of specific populations by identifying genetic bottlenecks that often occur in populations with small or widely fluctuating numbers of individuals. Second, genetic comparisons with introduced fishes suspected of hybridizing with native steelhead could help to identify instances of introgressive hybridization, which can weaken and eventually destroy the genetic distinctiveness of the native population. Third, in cases were transplantation of fish from other streams or hatcheries is necessary to promote recovery of a particular population, knowledge of the genetic make up of the source candidates would help in maintaining the genetic integrity of the population to be restored by identifying those sources most closely related to the recipient population. Finally, the results of such a survey could be used to investigate the relationship of steelhead to other Oncorhynchus lineages now being studied by members of the Genomic Variation Laboratory. 

  The objectives of the proposed study are to use a combination of rapidly evolving and relatively conserved nuclear and mitochondrial markers to 1) characterize genetic partitioning in Navarro River steelhead populations, 2) look for evidence of steelhead/ rainbow trout introgression in the watershed, and 3) assess the relationship of these steelhead populations to other steelhead and western trout lineages.     

Materials and Methods

   Sample Collection. Steelhead fin clip samples are being collected from numerous streams within the Navarro River drainage by Dr. Mike Johnson's group.

   Genetic Analysis. Whole genomic DNA will be isolated from fin clip samples using standard protocols. Microsatellite loci previously shown to differentiate between various lineages of the rainbow trout (O. mykiss spp.) complex will then be amplified from the isolated DNA samples via the polymerase chain reaction (PCR). Differences in the presence/ absence and frequencies of alleles will be used to characterize the population structure of steelhead within the Navarro River Drainage.         

Literature Cited

Moyle, P.B., R.M. Yoshiyama, J.E. Williams, and E.D. Wikramanayake .1995. Fish species of special concern in California. 2^nd ed. Final report prepared for the State of California, the Resource Agency, Department of Fish and Game, Inland Fisheries Division. 

Williams, J.E., et al. 1989. Fishes of North America endangered, threatened, or of special concern: 1989. Fisheries 14(6): 2-20.

Last Updated: 11/04/02