White Sturgeon Population Genetic Studies

For more information contact Andrea Schreier: amdrauch@ucdavis.edu

Background and Significance of Study

White sturgeon are large, diadromous fishes with a high dispersal capability that were presumed to exhibit some degree of spawning site fidelity. Spawning is known to occur in the Sacramento-San Joaquin, Columbia-Snake, and Fraser River drainages, although white sturgeon may be encountered in marine habitat or coastal streams outside of their natal drainage. Because of the complex nature of the duplicated white sturgeon genome, many questions regarding the population structure and dispersal behavior of white sturgeon remained unanswered. In this project, thirteen microsatellite loci were used to examine white sturgeon population structure both within and among drainages known to support spawning populations.

 

Results

I used the program Structure (Pritchard et al. 2000) to infer the number of populations both within each drainage (Sacramento-San Joaquin, Columbia-Snake, Fraser) and among drainages across the species range. Different patterns of population structure were revealed in each drainage. A single population was identified in the Sacramento-San Joaquin system despite that fact that spawning has been documented on both the Sacramento and San Joaquin Rivers. A complex isolation by distance pattern was observed in the Columbia-Snake drainage, with local gene flow among geographically proximate spawning sites but higher levels of genetic divergence among samples collected at opposite ends of the drainage. The genetic distinctness of the Kootenai River population within the Columbia-Snake was confirmed. Interestingly, the Fraser River system exhibited a hierarchical pattern of population structure, with strong levels of genetic divergence on either side of a putative barrier (Hells Gate) and additional substructure above that barrier. Distinct spawning populations in the Fraser River (above Hells Gate) exist in the absence of any physical barrier suggesting that white sturgeon exhibit stronger spawning site fidelity in that system. Additionally, we found that the federally listed Upper Fraser River population consisted of a mixture of individuals from the Middle Fraser and Nechako River populations.

Future Work

Population genetic analysis of white sturgeon samples collected in marine habitat or non-natal estuaries sought to elucidate marine migration behavior of white sturgeon. Although long-distance marine migrations of white sturgeon are known from mark-recapture data, it is unknown whether all populations with access to the ocean (Sacramento-San Joaquin, Lower Columbia, Lower Fraser) equally contribute marine migrants. More extensive analysis of marine migrants and potential source populations should better elucidate marine habitat use by this species.

Publications

Schreier, A.D., B. Mahardja, and B. May. 2012. Hierarchical patterns of population structure in the endangered Fraser River white sturgeon, Acipenser transmontanus, and implications for conservation. Can. J. Fish. & Aquat. Sci. 69:1968-1980. (pdf)

Drauch Schreier, A., B. Mahardja, and B. May. 2013. Variable patterns of population structure revealed across the range of the ancient octoploid white sturgeon, Acipenser transmontanus. Transactions of the American Fisheries Society 142(5):1273-1286. (pdf)