. The Canadian field-naturalist. Natural history. 34 The Canadian Field-Naturalist Vol. 116 c o r o a o c o r o a o o r o a o 1997 1999 Ostracods. Diptera i£ ii Trichoptera *I ^ •T •I Coleoptera ^ Total length group (mm) Total length group (mm) Figure 4. Numerical proportions (%) of primary prey taxa consumed by Flathead Chubs collected in July 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 < ). er, both tend to be confined to lentic wa
. The Canadian field-naturalist. Natural history. 34 The Canadian Field-Naturalist Vol. 116 c o r o a o c o r o a o o r o a o 1997 1999 Ostracods. Diptera i£ ii Trichoptera *I ^ •T •I Coleoptera ^ Total length group (mm) Total length group (mm) Figure 4. Numerical proportions (%) of primary prey taxa consumed by Flathead Chubs collected in July 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 < ). er, both tend to be confined to lentic waters and exhibit low densities in lotic habitats (Merrit and Cummins 1984; Pennak 1989). Therefore, the evi- dence suggests that the high flows in 1997 likely contributed to the altered diets by transporting prey taxa from the floodplain to the channel and/or by washing in-channel food resources away from sand- bars at a greater rate than during a typical flow year. In 1999, the consumption of Coleoptera during April and extending into the other sample months was pronounced. Although reported as Coleoptera, nearly all of the beetles observed in the Flathead Chub stomachs belonged to the family Cicindelidae (tiger beetles). Borror and White (1970) noted that tiger beetles, where present, tended to be very abun- dant and inhabited open shorelines and beaches. Numerous tiger beetles were observed on the sand- bars, and Borror and White (1970) also suggested that the larvae tend to burrow into sandy areas dur- ing their juvenile stages. We can only speculate about the mechanisms that made tiger beetles avail- able to Flathead Chubs; however, during the spring and summer of 1999, many tiger beetles were observed in the drift and it is possible that as sand- bars shift, late-stage larvae and possibly adults are expunged from their burrows and become more sus- ceptible to fish predation. Alternatively, Flathead Chubs may actively forage into the substrates. Live Flathead Chubs he
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