Spawning of Endangered Pallid Sturgeon in the Yellowstone River, Montana and North Dakota

The Pallid Sturgeon (Scaphirhynchus albus) was listed as endangered in 1990 under the United States Endangered Species Act of 1973 owing to lack of or extremely limited natural reproduction and recruitment, and declining stock status of the species in the Missouri and Mississippi rivers.  An extant wild stock comprised exclusively of old adults remains in the Missouri-Yellowstone river systems of Montana and North Dakota, and evidence suggests that recruitment has not occurred since the 1950s. Induced spawning of males and females from this stock is successful in hatcheries to produce viable offspring.  However, it is unknown if lack of natural reproduction in the Missouri and Yellowstone rivers is the cause for lack of recruitment in this portion of the species range, or if other recruitment bottlenecks occur.  Research during 2007-2013 involving telemetry of adults, application of reproductive indicators, and sampling for drifting free embryos was conducted to determine if reproduction by Pallid Sturgeon occurs.  Spawning was verified multiple years in the Yellowstone River based on aggregations of males and gravid females, and recaptures of spent females confirming egg release.  Spawning typically occurred during mid- to late-June in the lower 12 km of the Yellowstone River. Drift net sampling below known and suspected spawning locations yielded verification of successful hatch and drift-entry of wild-produced free embryos.  Based on these results, lack of Pallid Sturgeon recruitment in the upper Missouri River basin cannot be attributed exclusively to the lack of reproduction.