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US Fish & Wildlife Service FieldNotes

Sturgeon at the Extremes

Region 3, October 23, 2012
Small sturgeon captured from the Missouri River in a benthic trawl.
Small sturgeon captured from the Missouri River in a benthic trawl. - Photo Credit: n/a

What a difference a year can make on the Missouri River. The flooding that lasted much of last year gave way to drought this year. The Missouri River of 2012, with its lazy flows and large, beach-like sandbars, scarcely resembled the turbulent, roiling beast of 2011.

Areas that had torrential flows and were nearly devoid of fish during the flood are now characterized by modest flows teaming with fish. Conversely, what was great fish habitat during the 2011 flood was better suited this year for raccoons and cottonwood trees. However, at these polar extremes the Missouri River fish community adjusted as it always has. In fact, adaptability and toughness are hallmarks of big river fish species that call the Missouri River home.

While changes in habitat from last year to this year may seem extreme, these changes are but a trifle when compared to the radical shifts that have occurred across the millennia. Portions of the present day Missouri River were once covered by a huge inland sea. Glaciers have advanced and receded, drastically altering the landscape. During more modern times, the construction of dams, levees, and wing dikes has altered flows, changed channel morphology, disrupted natural processes, and reduced silt transportation. In response to these changes, both natural and manmade, species composition within the river has also changed.

Amazingly some species, such as the shovelnose sturgeon, have been able to scratch out a living for millions of years in this harsh, ever fluctuating environment. While shovelnose sturgeon have seemingly been able to adapt to these modern changes to the river, the closely related pallid sturgeon is struggling. It is believed that poor recruitment, possibly due to lack of appropriate nursery habitat for small sturgeon, is partially to blame. An understanding of how sturgeon, especially small, young sturgeon, utilize habitat at differing flows may be critical for recovery of pallid sturgeon.

The stark differences in river conditions from last year to this year provided us with an excellent opportunity to examine how these fish respond to different flows. The benthic otter trawl we utilized on the Pallid Sturgeon Population Assessment Project allowed us to catch numbers of small sturgeon while sampling a diversity of habitats. Anecdotal observations over the last couple years suggest that young sturgeon may shift locations under differing water levels to find habitats which provide the type of flows they prefer. Given the highly variable flows which characterize the Missouri River, it appears that any single habitat type may not be adequate.  Instead a suite of habitat types may be required to provide necessary nursery habitat for young sturgeon. Understanding how small sturgeon utilize habitat under differing flows will hopefully add to our overall understanding of these unique fish and aid in making decisions regarding habitat construction and flow modifications on the Missouri River.

Contact Info: Colby Wrasse, 573-234-2132 x30, colby_wrasse@fws.gov