Sturgeon and Paddlefish Spawning and Larval Dispersal in the Lower Missouri River

Sampling was conducted in the Lower Missouri River from mid-April through September along a single representative transect with eight stations equally spaced from the left to right descending bank.  A total of 683 embryos and larvae were captured.  Of these, 337 were identified in the laboratory as Scaphirhynchus sturgeon, with the remaining identified as Paddlefish (Polyodon spathula).  Genetic analyses of sturgeon samples indicated that 98.5% were Shovelnose Sturgeon and 1.5% were Scaphirhynchus hybrids.  Larvae collected over time indicated a shift in spawning of all species from the confluence upstream as the season progressed.  Spawning of sturgeon began in April and ceased by mid- June, with multiple peaks of spawning or waves of larvae.   Unexpectedly, sturgeon spawning resumed in mid-August and larvae were collected through September, though in smaller numbers than during spring.  In contrast, Paddlefish spawning occurred earlier and appeared more synchronous than sturgeon.  Paddlefish spawning and dispersal began April and was essentially complete by the end of May.  No Paddlefish were collected July-September.  Most free-drifting embryos of all species were collected near the thalweg, but larvae were collected at all sampled stations along the transect indicating some dispersal or exchange of drifting larvae outside the main channel.