

and that in July and Auqust catfish moved downstream with increased flow 

 levels in the Little Missouri River. He also indicates that constant 

 stream discharqe from mid-June to July will generally result in successful 

 reproduction. Droughts and flash floods will result in poor reproduction, 

 poor survival of young and brood stock reductions. While rapid fluctuations 

 in discharge were common in Beaver Creek during this period (Figure 21), 

 successful reproduction did occur. However, reproduction nay have been 

 reduced through environmental fluctuations. 



Northern pike . Only four northern pike were collected in Beaver Creek, 

 one at section 1 and the other three taken in the middle reaches of the 

 stream. There were at least two age-classes represented in the sample. The 

 northerns ranged in length from 427 to 693 mm and in weight from 500 to 

 2268 g. Since "jery few northerns were taken in Beaver Creek, it is 

 possible that they are in the creek as the result of stocking a stock- 

 water reservoir. Northerns do not contribute to the recreational fishery of 

 the stream. 



Species Diversity . Measures of species diversity are another tool for 

 the quantitative and qualitative description of fishery. Investigations 

 of longitudinal zonation in stream fishes reveal that, in relatively 

 unpolluted systems, diversity increases downstream (Sheldon 1968), meaning 

 the number of species increases with proximity to the river's mouth. a f^ 



Factors v/hich determine the upstream limits of particular species also 

 apparently contribute to the regulation of species diversity. A study 

 by Tramer and Rogers (1973) found that variations in water quality upset 

 the normal pattern of longitudinal zonation of fishes. Where streams 

 are undergoing stress fron pollution, species diversity may remain at 

 levels similar to those in the headwaters throughout the entire system. 

 The disappearance of some of the headwaters species is balanced by the 

 appearance of others, and gains in the abundance of one species are 

 canceled out by losses in another. Therefore, from baseline data, a 

 change in water quality can be reflected by a chanqe in species diversity. 

 It is a generally accepted concept that a large-scale environmental 

 stress exerted upon a diverse biological comunity results in a 

 reduction in species diversity (Cairns 1969). 



While species-diversity indices have been used extensively with benthic 

 macroinvertebrates to evaluate degradational environmental conditions, 

 they have only recently been applied to fish populations (Sheldon 1968, 

 Jackson and Harp 1973, and Harima and Mundy 1974). Shannon-Weaver diversity 

 indices were calculated for the 1977 and 1978 samples (Table 7). In 1977, 

 d ranged from 1.519 to 2.70 as compared to 0.996 to 3.022 in 1978. No 

 trend in d from source to mouth was noted in Beaver Creek similar in 

 magnitude to those calculated on other Montana prairie streams. 



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