Genetic Identification of Young-of-Year Reveals Low Reproduction of Endangered Pallid Sturgeon in the Middle Mississippi River

The range of the federally endangered pallid sturgeon (Scaphirhynchus albus) overlaps with the shovelnose sturgeon (S. platorynchus) with which it hybridizes. Young-of-year (YOY) pallid and shovelnose sturgeon and their hybrids are morphologically indistinguishable, thus accurate species identification depends on molecular markers. To estimate the relative abundances of YOY pallid, shovelnose, and hybrid sturgeon in the middle Mississippi River (MMR), larval trawls were conducted from April through October in 2008, 2009, 2010, and 2011. A total of 2694 sturgeon from 17 sites were collected. Individuals were measured to the nearest mm total length and preserved in ethanol. DNA was isolated from caudal fin tissue and amplified at 16 microsatellite loci via polymerase chain reaction. Fragments were analyzed by capillary electrophoresis. Species determinations were made employing Newhybrids software using baselines comprised of morphologically and genetically identified adult pallid and shovelnose sturgeon. Based on molecular markers, two YOY pallid and one YOY shovelnose/pallid hybrid were identified, while all other 2,691 were identified as shovelnose sturgeon. The estimated abundance of YOY pallid sturgeon is much lower than previously reported for the MMR and indicates low levels of pallid sturgeon reproduction.