Feeding ecology and food-web interactions of the fish assemblage in the upper Missouri River and lower Yellowstone River with an emphasis on pallid sturgeon conservation

Abstract

A conservation propagation program started in the late 1990s for the endangered Pallid Sturgeon Scaphirhynchus albus because the species was not recruiting in the Missouri River. Stocking has been successful and several studies have suggested that the survival of stocked Pallid Sturgeon in the upper Missouri River is relatively high. Stocking of hatchery-origin Pallid Sturgeon may have created an uncharacteristic population structure, which could lead to intraspecific and interspecific competition between juvenile Pallid Sturgeon, Shovelnose Sturgeon, and other fish species in the Missouri and Yellowstone rivers. The purpose of this study was to describe the diets of Pallid Sturgeon and Shovelnose Sturgeon, determine if gape size differed between species, and assess diets of many secondary and tertiary consumers to describe the food web of the upper Missouri and lower Yellowstone rivers. Pianka's index of diet overlap was highest in segments near Fort Peck Dam in the Missouri River. Diet overlap was low in the Missouri River below the confluence with the Yellowstone River and in the Yellowstone River. Gape size was slightly different between Pallid Sturgeon and Shovelnose Sturgeon suggesting it was not the mechanism for the shift to piscivory in Pallid Sturgeon. Chironomidae were the most abundant primary consumer in the upper Missouri River and lower Yellowstone River. Hydropsychidae were not abundant in either river system, but were frequently consumed by Goldeye, Channel Catfish, Shovelnose Sturgeon, and Stonecat in the Missouri River and Shovelnose Sturgeon in the Yellowstone River. Emerald Shiner were the most abundant secondary consumer in both rivers and the most frequently consumed secondary consumer by Pallid Sturgeon, in the Missouri River. In addition, Pallid Sturgeon in the Missouri River consumed Channel Catfish, Shovelnose Sturgeon, and either Sicklefin Chub or Sturgeon Chub. In the Yellowstone River, Pallid Sturgeon consumed Channel Catfish, Scaphirhynchus spp., and Stonecat. These results provide a foundation into key linkages among predators and prey to better understand the effects of stocking Pallid Sturgeon in the upper Missouri River and lower Yellowstone River.