TABLE 4. Summary of age-class strength of smallmouth bass in the Tongue River, 



1974-76. 



Northern pike were also captured in section IVb. The presence of small 

 northerns (236 mm or less in length) suggests that these fish are reproducing 

 in the river. The lower reaches of Hanging Woman Creek provide excellent 

 northern pike spawning habitat and probably act as a nursery for the 

 Tongue River population of northerns. 



The Tongue River supports the only rock bass population in Montana. The 

 greatest numbers of rock bass were found in sections IVb and Vb. All sizes 

 were represented in the samples. 



The greatest number of channel catfish was found in section lib, with 

 the largest fish weighing 4.88 kg (10.75 lb). Sauger were most abundant near 

 the mouth, in section lb, where they made up 13.1 percent of the total numbers 

 captured. The largest sauger caught weighed 2.2 kg (4.9 lb). 



SPECIES DIVERSITY 



Measures of species diversity are another tool for the quantitative and 

 qualitative description of a 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, as in the Tongue. Factors which 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 from 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 change in species 

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



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