Geographic patterns of genetic differentiation among collections of green sturgeon

The population structure of green sturgeon Acipenser medirostris has not previously been evaluated, although commercial and bycatch harvests may be impacting multiple populations of this species. Molecular markers were used to distinguish between green and white sturgeon A. transmontanus and to examine the genetic variation among green sturgeon collected from four locations along the West Coast of the United States between San Pablo Bay, California, and the Columbia River, Washington. Verification that putative green sturgeon samples were not white sturgeon was accomplished with a diagnostic restriction fragment length polymorphism in the mitochondrial cytochrome b locus. Genetic variation in green sturgeon was investigated using six microsatellite loci developed from published primers. Allele frequencies, the fixation index F-ST, and observed heterozygosities were determined at three disomic and three tetrasomic loci amplified from fin tissue samples. Pairwise FST values of 0.005 and -0.002 indicated no genetic differentiation between the Klamath and Rogue River collections or the Columbia River and San Pablo Bay collections. All other F-ST values among pairs of collections ranged between 0.06 and 0.08 and indicated a significant difference between collections from the Rogue and Klamath rivers and those from San Pablo Bay and the Columbia River. These results and highly significant G-tests of genotypic differences between these pairs of collections support the existence of genetic structuring in this species along the Pacific coast. These data suggest that not all spawning populations have been identified and that additional genetic research will be necessary to adequately describe the population structure of green sturgeon before effective management plans can be developed.