Characterization of Patterns of Sturgeon and Paddlefish Spawning and Dispersal in the Lower Missouri River to Guide Restoration Actions

Sturgeons and Paddlefish have declined in the fragmented and modified Missouri River.  Pallid Sturgeon, Shovelnose Sturgeon and Paddlefish are similar in having evolved a reproductive strategy with free embryos that disperse widely downstream over an extended period.  Characterization of dispersal patterns for these fishes was accomplished by sampling for free embryos weekly in the Lower Missouri River in 2012 and 2013.  Samples were collected from mid-April through July using icthyoplankton nets deployed near bottom and mid-water along a single transect.  Free embryos were assigned a developmental stage and identified to species.  The origins of collected free embryos were determined using models of flow and temperature-dependent development rates.   Most free-drifting embryos were collected near the thalweg, indicating these species likely disperse long distances.  No Pallid Sturgeon were collected.  Spawning of Shovelnose Sturgeon and Paddlefish shifted from the mouth of the river upstream as the season progressed.  Shovelnose Sturgeon spawning was widespread and occurred over an extended period whereas Paddlefish spawning occurred earlier and was more synchronous.  Results contribute to understanding dispersal in these species and underscore the importance of identifying where spawning occurs on the landscape to effectively make decisions about flow modification and habitat restoration to promote species recovery.