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Fishery researchers and managers have found that in most cases the ratios shown in Figure 1 more clearly separated the species in the upper basin States than they did in the lower basin States. They also found that upper basin specimens of both species are typically larger in average weight and length than species collected from the lower Missouri River and Mississippi River. Although in most instances pallid sturgeon are lighter in color than shovelnose sturgeon, coloration cannot consistently be relied upon as a means of separating the two species (Kallemeyn 1983). The pallid sturgeon is one of the largest fish species found in the Missouri/Mississippi River drainage, with specimens approaching 39 kilograms (kg) (86 lbs) reported (Gilbraith et al. 1988). Adult pallid sturgeon collected from the upper Missouri River are generally larger than adults collected from the middle Missouri River and Mississippi River. The maximum recorded weight of a pallid sturgeon collected from-the Missouri River in Montana and North Dakota is approximately 39 kg (86 lbs). From the Missouri River in South Dakota and Nebraska, the maximum weight recorded is approximately 21 kg (46 lbs). In the Mississippi River the maximum weight recorded is approximately 12 kg (26 lbs). Historical Distribution and Abundance: The historic range of pallid sturgeon as described by Bailey and Cross (1954) encompassed the middle and lower-Mississippi River, the Missouri River, and the lower reaches of the Platte, Kansas, and Yellowstone Rivers (Figure 2). The pallid sturgeon was not recognized as a species until 1905, therefore little is known concerning its early abundance and distribution (Pflieger 1975), but available information suggests a probable decline since the species was described. Forbes and Richardson (1905) and Bailey and Cross (1954) indicated that the species .was always uncommon. Of the 250 pallid sturgeon reported by Bailey and Cross {1954), approximately 76 percent were collected from the Missouri River in Montana and the Dakotas; most were collected in the upper ends of the five main stem reservoirs as they were filling. At the time of their original description, pallid sturgeon composed 1 in 500 river sturgeon captured in the Mississippi River at Grafton, Illinois (Forbes and Richardson 1905). Pallid sturgeon were more abundant in-the lower Missouri River near West Alton, Missouri, where they composed one-fifth of the river sturgeon captured (Forbes and Richardson 1905). Bailey and Cross (1954) provided additional information on the proportions of pallid sturgeon in the total commercial catch of river sturgeon from various parts of the species' range as follows: Kansas River at Lawrence, Kansas (8 percent); Missouri River in South Dakota, 3 of 62 specimens (5 percent); and Mississippi River at New Orleans, 3 of 4 specimens (75 percent). Fisher (1962) recorded 4 of 13 river sturgeons (31 percent) from the Missouri River in Missouri as pallid sturgeon. Comparable commercial catch records are not available for the upper river reaches where commercial fishing was light or nonexistent. 3