Broadly defined, a forage fish is any utilized by another fish as a food 

 source. Most fish species during their first year of life are small enough 

 to be utilized as food and should be considered as part of the forage base. 

 The availability of age game and nongame species depends on their habits. 

 Species whose young are pelagic and typically exhibit schooling patterns 

 would be more susceptible to predation than those species whose young do 

 not normally school and commonly seek shelter among the rocks, brush piles, 

 or instream debris. Since the habitat requirements of most age stream fishes 

 are poorly understood, it is not possible to determine the availability 

 of age game and nongame fishes as forage at this time. For this study, 

 forage fish are defined as those species which, as adults, seldom exceed 

 six inches in length. This would include all of the cyprinids and certain 

 others such as the stonecat and mountainsucker. These species usually remain 

 a food source for their entire lives. 



STUDY AREA 



From the mouth of the Bighorn River, the lower Yellowstone flows a 

 distance of 476 km (295 mi) to its confluence with the Missouri River. The 

 river gradient averages less than .50 m/km (2.6 ft/mi). Average flow at 

 Miles City in August 1975 was 460 m3/sec and 260 m^/sec in September. At 

 Sidney, 248 km (154 mi) below Miles City, average discharges were 460 m^/sec 

 and 275 m-^/sec during the same months. 



The Yellowstone River, including the sections from the Bighorn River to 

 Forsyth and from Glendive to the mouth, is essentially a braided river with 

 numerous side channels. Only the 228 km of river from Forsyth to Glendive 

 can be described as meandering. Many side channels contain water only during 

 the spring runoff. As the water level drops in midsummer, still backwater 

 areas remain at the lower end of the side channels. 



The morphology of the river is maintained by annual high flows. The 

 physical character of the river provides a variety of habitats including 

 shallow and deep riffles, pools, and still backwaters. This natural diversity 

 creates the conditions which allow the presence of a diverse aquatic community. 

 Forty-five of 49 fish species in the Yellowstone River are present in the 

 lower river, which supports a warm-water fishery (Peterman and Haddix 1975). 

 Twelve species are classified as game fish by the Montana Fish and Game 

 Department. More than 70 species of benthic macroinvertebrates are reported 

 for the lower river (see Report No. 5 in this series). 



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