Platte River and is uncommon in the Missouri River bordering Nebraska. In July 2000, a specimen was captured near Schuyler, Nebraska; that constitutes the furthest upstream documented locality in the Platte River. The pallid sturgeon was described from specimens captured in the Mississippi River near Grafton, Illinois, by Forbes and Richardson (1905). Specimens lack the spiracle found in the genus Acipenser, are light in color, and have a caudal peduncle that is fully armored and laterally compressed (Figure 1-5). The breast or belly of the pallid sturgeon is naked; this distinguishes it from the shovelnose sturgeon, whose belly is covered with scale-like plates. Keenlyne et al. (1994) measured shovelnose and pallid sturgeon from the upper Missouri River drainage and found overlap in morphometric characters between the two species. Sheehan et al. (1999) developed an index with meristic and morphometric characters to distinguish pallid and shovelnose sturgeon. Differences between species of the genus Scaphirhynchus have been debated over the last several years (Phelps and Allendorf 1983), but recent genetic studies are providing valuable insight into the evolutionary relationships of these species and have confirmed the genetic distinction between pallid and shovelnose sturgeon (Campton et al. 2000; McQuown et al. 2000; Simons et al. 2001; Birstein et al. 2002). There is no way to distinguish male and female pallid sturgeon visually.
A common denominator in the distribution of sturgeon species appears to be access to flowing freshwater, at least for spawning and initial development. That is especially true for members of the genus Scaphirhynchus (also known as river sturgeons), which spend virtually their whole lives in riverine environments. Sturgeons are long-distance travelers. Tagging studies have documented movements of well over 100 km. Sturgeon eggs are demersal and adhesive. Shortly after hatching, the larvae become buoyant and drift with the current.
Pallid sturgeon were found in the Mississippi River from near Keokuk, Iowa, downstream to the Gulf of Mexico, and in the Achafalaya River in Louisiana. The main part of their range is the Missouri River, from its confluence with the Mississippi River upstream to Fort Benton, Montana (Figures 7-1 and 7-2). In addition, pallid sturgeon have been documented from downstream reaches of several major tributaries of the Missouri River. In Kansas, they are known only from the lower 65 km of the Kansas River, mostly during the time of floods. In Nebraska, they have been captured up to 46 km upstream of the mouth of the Platte River. In Montana, their distribution extends 113 km up the Yellowstone River. Damming, water diversions, flood control, and channelization have modified rivers throughout much of its range (Keenlyne 1989). Today, the distribution of pallid