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Diet composition and overlap of larval pallid sturgeon and shovelnose sturgeon from the upper Missouri River

Colt Holley*, Pat Braaten, Barry Poulton, Edward Heist, Levi Umland, Tyler Haddix

*Corresponding author:

ABSTRACT: Early life stages of pallid sturgeon Scaphirhynchus albus are rarely collected, and thus information on their biology and ecology is extremely limited. Seventy-five larval pallid sturgeon (25–110 mm) and 148 larval shovelnose sturgeon S. platorynchus (15–95 mm) were sampled by trawl from the upper Missouri River in 2019. Stomach contents were identified to compare food use and diet overlap between the two sturgeon species at the order, family, and genus levels of taxonomic prey identification. Analyses were conducted with sites pooled and sites separated by the confluence of the Yellowstone River. Abundance of dominant prey in the gut (Diptera larvae) increased with fish length for both species, and regression slopes were similar. Diet overlap at pooled sites decreased from 0.94 to 0.49 when prey were identified to order and genus, respectively, and decreases in diet overlap at individual sites were more pronounced. Larval pallid sturgeon consumed a maximum of 11 unique taxa; whereas shovelnose sturgeon consumed 6 taxa not consumed by pallid sturgeon. These results indicate that larval diets are similar between species when evaluated at coarse taxonomic scales, but at fine taxonomic scales, notable differences exist. As information about the diets of larval pallid sturgeon captured from a riverine environment are scarce and the use of shovelnose sturgeon as an indicator of available suitable food and habitat and as a dietary surrogate for pallid sturgeon has been under consideration, our results suggest that caution be exercised in modeling efforts or management actions relating to surrogacy.