Validation is critical when considering potential surrogates for endangered species research. The pallid sturgeon Scaphirhynchus albus is federally endangered in the USA, whereas the congeneric shovelnose sturgeon S. platorynchus is common. Inadequate food availability during early life history is a hypothesized factor limiting recruitment of pallid sturgeon in the lower Missouri River, USA, and an established surrogate relationship with shovelnose sturgeon would dramatically expedite research efforts related to potential food limitation. During 2018, 4 exogenously feeding pallid sturgeon larvae were captured concurrently with multiple shovelnose sturgeon, providing a critical opportunity to evaluate diet surrogacy using individuals captured from the same locations. We found that both species primarily consumed ephemeropterans but chironomids were also frequent prey. Over 90% of the pallid sturgeon prey items belonged to taxa also consumed by shovelnose sturgeon. Additionally, we often observed high diet similarity between these congeners. As for total prey weight, pallid sturgeon consumption was similar or higher compared to similarly sized shovelnose sturgeon. Although the sample size was limited, this study supports the hypothesis that larval pallid sturgeon are capable of finding food in the lower Missouri River and exhibiting diet similarity with shovelnose sturgeon. We also provide the first quantification of prey weight for wild-produced larval pallid sturgeon, which consumed relatively large amounts of prey in the wild during the critical transition from endogenous to exogenous feeding.

Insufficient food during early life could limit the population growth of endangered Pallid Sturgeon Scaphirhynchus albus in the lower Missouri River. Shallow-water habitat restoration is intended to provide nursery benefits, including food, for young sturgeon, but the effect of shallow-water habitat on their diet is unknown. Age-0 Pallid Sturgeon are rare, providing little opportunity for direct evaluation; however, studying the closely related and abundant Shovelnose Sturgeon S. platorynchus may provide valuable information to guide habitat restoration efforts. We compared diet, body condition (lipid content), and change in body weight (24-h bioenergetics simulation) for postdrift, age-0 sturgeon among five reaches ranging widely in shallow-water habitat availability. Lipid content of satiated and emaciated laboratory-reared individuals were compared with that of wild-caught fish. In general, shallow-water habitat availability appeared to have little effect on the variables examined. Regardless of reach, wild-caught fish primarily consumed chironomids, and empty stomachs were rare. Additionally, differences in prey weight, lipid content, or the modeled change in body weight did not usually correspond to differences in shallow-water habitat availability. Instead, we found annual differences, as prey weight consumed and the percentage of fish with modeled weight gain was often higher in 2015 than 2014, while the opposite was true for the percentage of fish with lipid content values that were comparable with the emaciated laboratory standard. Overall, our findings complement recent suggestions that shallow-water habitat restoration efforts, as previously implemented, may not benefit sturgeon populations. Our results coupled with previous research suggest that the lower Missouri River prey base can support a stable Shovelnose Sturgeon population; however, additional research is needed to determine whether this applies to Pallid Sturgeon.

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A lack of nutritious food during the first year of life is a hypothesized factor that may limit survival of endangered pallid sturgeon Scaphirhynchus albus in the lower Missouri River (LMOR). Unfortunately, information for age-0 pallid sturgeon diets remains limited, but diet analyses for age-0 Scaphirhynchus spp. (sturgeon hereafter) have occurred. Little information, however, exists on age-0 sturgeon diets in the LMOR; thus, our primary objective was to document age-0 sturgeon diets in this system. We examined guts contents from 30 individuals, which were genetically identified as shovelnose sturgeon Scaphirhynchus platorynchus, and three stomachs were empty. The remaining age-0 shovelnose sturgeon consumed chironomid larvae almost exclusively (>98% of prey items consumed). Our results were similar to studies conducted in other systems, and it appears unlikely that a lack of nutritious food was a major factor affecting the individuals captured during this study. This effort provides important information to help guide ongoing adaptive management efforts in the LMOR.