Emigration of Hatchery-Reared Pallid Sturgeon through Gavins Point Dam

The endangered Pallid Sturgeon (Scaphirhynchus albus) population in the Missouri River is maintained by stocking hatchery-reared fish.  Due to genetic differences among Pallid Sturgeon throughout their range, locally-collected broodstock are used for propagation, with the exception being the Missouri River between Fort Randall Dam (SD) and Gavins Point Dam (NE-SD).  Pallid Sturgeon stocked in this reach are progeny from broodstock collected in Montana and North Dakota.  Downstream emigration of these fish maintains gene flow that likely occurred before impoundment, but emigration of these individuals has not been formally evaluated.  Therefore, we evaluated recapture data from marked Pallid Sturgeon to improve our understanding of downstream emigration through Gavins Point Dam.  Of the 12,030 Pallid Sturgeon stocked in this reach, 893 (7%) were captured in the stocking reach and 219 (1.8%) were captured downstream of Gavins Point Dam.  The number of new emigrants found each year has increased since 2004 and peaked at 30 in 2012 and 2014.  If survival and recapture probabilities are similar upstream and downstream of Gavins Point Dam, then emigration may be substantial (e.g., 19%) and it may be necessary to reconsider current stocking procedures for Pallid Sturgeon.