Abstract
Two species, the Siberian sturgeon, Acipenser baerii , and stellate sturgeon, A. stellatus , were studied using mitochondrial DNA (mtDNA) (D‐loop, cytochrome b (cyt‐ b ) and ND5/6 genes) sequencing to determine whether traditionally defined subspecies correspond to taxonomic entities and conservation management units. Initially, several mtDNA regions for each taxon ( A. baerii : 737 bp D‐loop, 750 bp ND5, 200 bp ND6, and 790 bp cyt‐ b; A. stellatus : 737 bp D‐loop and 600 bp ND5) were examined. The D‐loop was the most variable region and was sequenced for 35 A. baerii and 82 A. stellatus individuals. No fixed, diagnostic differences were found between any of the subspecies. Geographical structuring of haplotypes was observed within A. baerii , and gene flow estimates suggest isolation of the A. baerii baicalensis subspecies and the Yenisie and Lena River populations. No intraspecific subdivisioning was found within the genetic data for A. stellatus . The use of the phylogenetic criterion (fixed diagnostic differences) for identifying conservation units is compared to the rationale and results of other methods. Overall, morphologically and geographically based subspecies designations within Acipenseridae may not directly correspond to the biological entities appropriate for management and should not be used for conservation programmes without genetic support.