Size-Dependent Trophic Patterns of Pallid Sturgeon and Shovelnose Sturgeon in a Large River System

Abstract

This study compared patterns of δ15N and δ13C enrichment of pallid sturgeon Scaphirhynchus albus and shovelnose sturgeon S. platorynchus in the Missouri River, United States, to infer their trophic position in a large river system. We examined enrichment and energy flow for pallid sturgeon in three segments of the Missouri River (Montana/North Dakota, Nebraska/South Dakota, and Nebraska/Iowa) and made comparisons between species in the two downstream segments (Nebraska/South Dakota and Nebraska/Iowa). Patterns in isotopic composition for pallid sturgeon were consistent with gut content analyses indicating an ontogenetic diet shift from invertebrates to fish prey at sizes of >500-mm fork length (FL) in all three segments of the Missouri River. Isotopic patterns revealed shovelnose sturgeon did not experience an ontogenetic shift in diet and used similar prey resources as small (<500-mm FL) pallid sturgeon in the two downstream segments. We found stable isotope analysis to be an effective tool for evaluating the trophic position of sturgeons within a large river food web.

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

“…Both Pallid Sturgeon and Shovelnose Sturgeon are invertivores during their early life (Braaten et al 2007;Harrison et al 2014) and Shovelnose Sturgeon remain so throughout life (French et al 2013). Pallid Sturgeon exhibit a higher degree of piscivory as they age (Gerrity et al 2006;French et al 2013). We suggest that the high density of macroinvertebrates around island complexes draws Scaphirhynchus sturgeons to these habitats (see Spindler et al 2012).…”

“…Subsequently, islands harbor a high density and diversity of riverine fauna (Thorp 1992;Gurnell and Petts 2002;Gurnell et al 2005;Ricaurte et al 2012). Both Pallid Sturgeon and Shovelnose Sturgeon are invertivores during their early life (Braaten et al 2007;Harrison et al 2014) and Shovelnose Sturgeon remain so throughout life (French et al 2013). Pallid Sturgeon exhibit a higher degree of piscivory as they age (Gerrity et al 2006;French et al 2013).…”