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Fish of several species were collected from the Yellowstone River near 

 Miles City and Intake. Most of them were captured by electrofishing in August 

 of 1975 and 1976. Stomach contents from 145 mature fish were identified, 

 counted, and measured volumetrically. Quantitative results were tabulated for 

 shovelnose sturgeon, goldeye, channel catfish, sauger, and burbot. 



Insects were the major foods of sturgeon, goldeye, and catfish. Aquatic 

 Insects of riffles were of greatest importance to all three species but were 

 consumed in greatest amounts by shovelnose sturgeon. Goldeye and catfish 

 stomachs contained terrestrial insects as well. Only the catfish diet included 

 fish. 



From a previous study of the aquatic food organisms available in August 

 and September, Traverella alhertana was the most abundant (Report No. 5 

 in this series). Ivlev's electivity index revealed that this species of 

 mayfly was eaten by sturgeon in portions equal to its availability, but 

 goldeye and catfish selected it over other foods. 



Hydropsyche is the dominant species of riffle insects during the fall and 

 winter months on the river (Report No. 5). Based on that fact and on the 

 results of studies in other rivers, it is expected that this genus of caddis- 

 fly becomes the major food item of sturgeon following the emergence of 

 Traverella in September. 



Flathead chubs and minnows of the genus Hyhognathus were common in the 

 diets of sauger and burbot. In addition, sauger stomachs contained longnose 

 dace and catfish fry. Stonecats were important in the burbot diet. Young 

 sauger and burbot are highly dependent on invertebrates for food. 



The impact of reduced flows would be felt by all members of the food 

 chain. Traverella and Hydropsyche, the most abundant benthic insects, are 

 the most important foods of riffle fishes and prefer relatively high water 

 velocities; they would suffer the greatest loss during low flows. As food 

 and riffle space declines, fish growth is restricted until predator populations 

 stabilize or fall to levels that can be supported by the altered habitat. Of 

 the fish that feed on benthic insects, reduced flows would be most detrimental 

 to the growth and production of shovelnose sturgeon, goldeye, channel catfish, 

 and young-of-the-year sauger and burbot. 



The maintenance of side channels and backwaters is dependent on high 

 spring flows. As side-channel flow diminishes in late summer, sufficient dis- 

 charge must remain to ensure the existence of backwater areas. A reduction in 

 backwaters would result in a direct loss of habitat to fish species which 

 frequent these still waters. Piscivorous species affected by such alteration 

 include mature sauger and burbot, channel catfish, northern pike, and crappie. 



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