this section is poor due to a near absence of hiding cover. 

 Other influences on the fishery are difficult to detect because 

 poor habitat probably limits the fishery in this section. 



The general decline in trout populations, particularly for 

 cutthroat trout, in this reach may be related to metals toxicity. 

 Tailings released during the 1975 dam failure were suspected to 

 have been deposited in beaver pond areas of this reach. In 

 addition, evidence of downstream movement of tailings below the 

 beaver dams has been collected in 1988 (J. Moore, pers.comn.). 



Low summer streamflows, accompanied by accumulated fine 

 sediments in the absence of flushing flows, may also contribute 

 to the decreased densities of trout observed during 1988. 

 Effects of low streamflows are particularly noticeable in the 

 lower portion of this reach where the permeable alluvium lowers 

 the groundwater table (Coffin and Wilke 1971) . 



Reach 2: Lincoln to Nevada Creek 



Water lost to the subsurface in the upper river reappears in 

 Reach 2 in the form of groundwater seepage and spring creeks. 

 This additional water has a significant influence on the fishery 

 of Reach 2. In addition, the gradient decreases and structural 

 cover (particularly log jams) becomes more abundant. The 

 predominant trout species in this reach is brown trout. The 

 presence of brown trout in this reach probably results from a 

 combination of the groundwater influence, which is a preferred 

 component in brown trout spawning habitat, and the abundance of 

 structural cover. 



Trout population estimates were conducted in the Poorman- 

 Dalton and Canyon Sections during the early 1970 's, and repeated 

 during 1988. During both surveys, brown trout densities were 

 significantly higher in the Poorman-Dalton Section than in the 

 Canyon Section, located about 13 miles downstream. Higher 

 densities in the Poorman-Dalton Section are probably, in part, 

 due to its proximity to the preferred brown trout spawning area 

 where extensive groundwater recharge occurs. Surveys of brown 

 trout YOY are highest in this area, and progressively decrease in 

 density downstream from this area. Spawning in this area appears 

 to be the primary source of brown trout recruitment for Reach 2. 



Mature brown trout (age II and older) densities have not 

 significantly changed between the two sampling periods. Yearling 

 brown trout densities, however, have decreased significantly in 

 both sections since the early 1970 's. This decline in numbers of 

 juvenile fish may be related to drought conditions and below 

 normal streamflows. A similar observation was made in the 

 Bitterroot River where low streamflows resulted in decreased 

 numbers of juvenile brown trout, but did not significantly effect 

 numbers of adults (Spoon 1987) . Increased juvenile mortality 



38 



