Riverscape Genetics of the Endangered Pallid Sturgeon

The pallid sturgeon (Scaphirhynchus albus) is an endangered fish native to the Missouri and Mississippi River drainages from Montana to Louisiana.  Across its broad geographic range, it is morphologically heterogeneous; southern specimens are typically smaller and more similar to the congeneric shovelnose sturgeon (S. platorynchus) than are northern specimens.  Pallid sturgeon are also genetically heterogeneous; there are significant differences in microsatellite allele frequencies among regions.  Genetic structuring exists within the pallid sturgeon’s range representing two distinct groups at the extremes of the species range with a middle intermediate group representing the lower Missouri and middle Mississippi rivers.   These data suggest a pattern of isolation by distance.   Much of the pallid sturgeon’s northern range in Montana, North Dakota and South Dakota, has been altered by dams and reservoirs. Here natural recruitment has not been documented with more than 15 years of sampling effort and artificial spawning of wild caught adult pallid sturgeon maintains the population.  Within the lower Missouri River, recruitment is rare necessitating limited augmentation.  However, in the Mississippi River, natural recruitment occurs, and data currently do not support the need for artificial supplementation.  The US Fish and Wildlife Service  identifies four management units based largely on the concept of physiographic provinces defined from data on other species augmented with  empirically derived genetic data.  Wild pallid sturgeon from the middle portion of the species’ range (downstream from Gavins Point Dam, South Dakota, the lowermost dam on the Missouri River), are genetically similar to those collected in the northern reaches despite more than fifty years of isolation.  Most pallid sturgeon from the middle Mississippi River genetically assign to a different group than those in the lower Missouri River, despite the lack of significant barriers to migration and documented movements between the Missouri and Mississippi rivers.  These data indicate that genetic structuring of pallid sturgeon is natural and predates anthropogenic migratory barriers.  The four management units are good approximations of the natural variation that occurs across the pallid sturgeon’s range.  However, landscape-level genetic analysis coupled with GIS-based tools can refine the boundaries between management units and help to identify migrants from other regions, which is essential to minimize the risks associated with brood fish selection for conservation propagation.