Genetic Tools Indicate Low Pallid Sturgeon Recruitment and High Rates of Hybridization in the Lower Missouri and Mississippi Rivers

The endangered Pallid Sturgeon (Scaphirhynchus albus) is native to the Missouri River and the Mississippi River below the confluence with the Missouri River.  Failed recruitment in the upper (UMO) and lower (LMO) Missouri River and hybridization with the Shovelnose Sturgeon (S. platorynchus) in the LMO and the middle (MMR) and lower (LMR) Mississippi River hamper recovery of the species. Recovery efforts include stocking pallid sturgeon using wild broodstock in the UMO and LMO, but not the MMR or LMR, where natural recruitment is presumed to occur.  Genetic tagging using genotypes of known broodstock parents and reconstructed genotypes of unsampled parents based on known offspring demonstrate that a large fraction of unmarked pallid sturgeon in the LMO and MMR are hatchery origin fish, especially in the MMR, where a single year class is dominant.  Genetic distinctiveness between presumably wild Pallid and Shovelnose Sturgeon morphotypes decreases from the UMO to the LMO and the species are difficult to discriminate in the MMR and LMR where they likely comprise a hybrid swarm.  We genotyped more than 2000 larvae and young of year Scaphirhynchus in the LOM and MMR and detected only two pallid sturgeon larvae in the MMR and none in the LMO.