Status and Habitat Use of Scaphirhynchus Sturgeons in an Important Fluvial Corridor: Implications for River Habitat Enhancement

In the central United States, recovery efforts for populations of the federally endangered Pallid Sturgeon Scaphirhynchus albus have been ongoing since its listing in 1990. Its congener, the Shovelnose Sturgeon S. platorynchus, has also recently been listed as threatened where it overlaps with Pallid Sturgeon. The status of both species in the Mississippi River is unknown and so are habitat enhancement priorities that would benefit their recovery. Using field data collected from 2002 through 2005, we (1) estimated the adult population size of both species using mark-recapture methods and (2) quantified habitat use of these sturgeons with multiple gears to elucidate habitat enhancement priorities in the middle Mississippi River-an important fluvial corridor that connects the upper Mississippi River and Missouri River basins with the lower Mississippi River basin. Population size was estimated to be 1,516 (95% CI = 710-3,463) Pallid Sturgeon (five individuals per river kilometer [rkm]) and 82,336 (95% CI = 59,438-114,585) Shovelnose Sturgeon (266 individuals/rkm). Our population estimate showed a low relative abundance of Pallid Sturgeon in this corridor. However, the population estimate suggests Pallid Sturgeon abundance has increased since its listing in 1990. Shovelnose Sturgeon were more abundant than Pallid Sturgeon, but whether the Shovelnose Sturgeon population is increasing, decreasing, or stable remains unknown. Among 10 habitat types, both species were most frequent at the downstream ends of alluvial islands. Pallid and Shovelnose sturgeons were restricted to flow rates < 1.0 m/s, and their abundance was greatest in depths ranging from 4.5 to 14 m. We suggest alluvial island enhancement may facilitate sturgeon recovery in the middle Mississippi River.