. The Canadian field-naturalist. Natural history. 2002 Fisher, Willis, Olson, and Krentz: Flathead Chubs in Upper Missouri 35 c o o a o c o -E o a o c o o a o 100 80 60 40 20 98 75 60 45 30 15 0 24 â 18 â 12 6 \ 0 ⢠Diptera 1 1 ' â T^ i ^ T T 1997 1999 Ephemeroptera â¢I. Total length group (mm) Total length group (mm) Figure 5. Numerical proportions (%) of primary prey taxa consumed by Flathead Chubs collected in August of 1997 and 1999 from the Missouri River, North Dakota. For each pair of bars (1997 and 1999), a statistical comparison was conducted. Those pairs with a * designation were si
. The Canadian field-naturalist. Natural history. 2002 Fisher, Willis, Olson, and Krentz: Flathead Chubs in Upper Missouri 35 c o o a o c o -E o a o c o o a o 100 80 60 40 20 98 75 60 45 30 15 0 24 â 18 â 12 6 \ 0 ⢠Diptera 1 1 ' â T^ i ^ T T 1997 1999 Ephemeroptera â¢I. Total length group (mm) Total length group (mm) Figure 5. Numerical proportions (%) of primary prey taxa consumed by Flathead Chubs collected in August of 1997 and 1999 from the Missouri River, North Dakota. For each pair of bars (1997 and 1999), a statistical comparison was conducted. Those pairs with a * designation were significantly different (P < ). removed the staging substrates, either repelling the beetles away from the river bottom in search of bet- ter habitats or transporting the organisms out of the feeding area. The consumption of backwater-originated prey resources by Flathead Chubs during 1999, and more extensively in 1997, suggests that backwater prey production could be important to Flathead Chubs in the Missouri River, particularly during high-flow periods. In a relatively backwater-poor section of the Yellowstone River, Montana, upstream from our study site, Scarnecchia et al. (2000) also collected Flathead Chub in 1997, but found that 98% of the stomachs were empty. The high 1997 flow rates may have transported more typical Flathead Chub prey into unusable areas; therefore, the increased con- sumption of backwater-oriented food resources may have been a compensatory effort to obtain nutrition. We did not document any empty stomach propor- tions greater than 70%, and for most Flathead Chub length categories and sample periods, empty stom- ach proportions were typically < 40% (Table 4). It is unclear if the backwater prey availability was suffi- cient to provide adequate rations for the Flathead Chub population. Age and Growth To complete the back-calculation process, we needed to obtain a Flathead Chub intercept, or a- value, for the scale radius to total body le
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