Scaphirhynchus albus

Scaphirhynchus albus formerly was thought to be genetically identical to S. platorhynchus (Phelps and Allendorf 1983).

Data from 5 nuclear DNA microsatellite loci indicate that pallid and shovelnose sturgeon are genetically distinct at three sympatric localities; pallid sturgeon from two northern populations in the upper Missouri River are genetically distinct from a population in the Atchafalaya River in Louisiana, suggesting that northern and southern populations are reproductively isolated (Tranah et al. 2001). Shovelnose sturgeon from the three localities are genetically indistinguishable. Individuals identified morphologically as hybrids are genetically distinct from pallid sturgeon but genetically indistinguishable from shovelnose sturgeon; these results are the converse of the results based on mtDNA published elsewhere (Tranah et al. 2001).

Genetic data (Campton et al. 2000, Tranah et al. 2001, Heist and Schrey 2006) suggest that the pallid sturgeon comprises two distinct groups at the extremes of the species' range with a middle intermediate group representing the lower Missouri and middle Mississippi Rivers. This pattern is suggestive of a pattern of isolation by distance, with gene flow more likely to occur between adjacent groups than among geographically distant groups, and thus, genetic differences increase with geographical distance (USFWS 2007).

Large range and area of occupancy in larger channels of the Mississippi-Missouri river system and Atchafalaya River; range much reduced by dams in the upper Missouri River; habitat changes and barriers have resulted in limited natural recruitment and continuing declines in wild populations in the Missouri River basin; recent increased sampling effort has revealed larger populations than were known at the time of federal listing; ongoing stocking of hatchery-produced sturgeons may eventually lead to increases in the spawning population.

Range includes the Missouri River (from mouth to Fort Benton, Montana), lower Yellowstone River, lower Platte River, Mississippi River downstream from its junction with the Missouri River and upstream at least several kilometers from the Missouri River, and Atchafalaya River in central Louisiana (Reed and Ewing 1993, USFWS 2007). Occasional sightings have occurred near the mouths of various other large tributaries of the Mississippi River (e.g., Big Sunflower River and St. Francis River) and Missouri River (e.g., Kansas River and Platte River), but these instances may reflect fishes utilizing unusual flow conditions (USFWS 1989). The lower Yellowstone River and lower Platte River may be significant spawning tributaries (see USFWS 2007).

USFWS has revised its original 6 priority management areas (USFWS 1993) to 4 based on: genentic information, mophology, biogeography and speciation associated with physiographic provinces, shared threats, and management (USFWS 2014). The various reaches within the species range are considered occurrences.

Construction and operation of large dams and river channelization have eliminated and degraded preferred sturgeon habitat (Pflieger and Grace 1987). On the main stem of the Missouri River, approximately 36 percent of riverine habitat within the pallid sturgeon's range was eliminated by construction of six massive earthen dams between 1926 and 1952 (USFWS 1993); the dams are believed to block migrations, and the reservoirs probably inundated historical spawning and nursery areas. Another 40 percent has been channelized. The remaining 24 percent has been altered due to changes in water flows caused by dam operations (USFWS 1993). USFWS (2007) concluded that the species is still threatened by habitat loss and inadequate regulatory mechanisms in all or portions of the range. Habitat changes have severely reduced or eliminated successful reproduction. The low level of natural recruitment is a major concern and impediment to recovery.

Past commercial exploitation likely exceeded biological recruitment. Illegal commercial harvest is currently occurring in portions of the lower Missouri River and Mississippi River; pallid sturgeon exhibits lower ages and higher mortality rates in areas where shovelnose sturgeons are commercially harvested (Colombo et al., in press). This threat is likely to increase as caviar sources are reduced world-wide and caviar prices increase (USFWS 2007).

Limited data suggest that contaminants may have some affect on reproduction (USFWS 2007).

Significant hybridization with shovelnose sturgeon has been documented (USFWS 1989, Wills et al. 2002). However, it is unclear whether hybridization is actually a threat (USFWS 2007).