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DISCUSSION 



The sampling of fish populations in this study has raised more questions than 

 the effort has answered so far. Recent literature searches and on-going fisheries 

 work further clouded our results with uncertainty as to what exactly we are 

 measuring in the limited fish population sections. Are we measuring the carrying 

 capacity of that section or the result of some limiting factor either spatially 

 or temporally removed from that site? The ramifications of this difficulty is 

 that our sampling design may only show impacts if the summer habitat contains 

 the limiting factor (s) on the particular population. Studies of cutthroat trout 

 in the Flathead River system indicate that some fish enter the interstitial 

 areas in the substrate while some adult fish move to pools in the larger river 

 system (personal communication with Pat Graham). 



Campbell and Neuner, 1985, reported that rainbow trout in the Cascade 

 mountain streams have seasonal behavior changes which follow water temperature. 

 A hiding response begins at 3C and few trout can be found in the water column 

 below 3C. The seasonal change creates an alternative emphasis on food in 

 summer and cover in winter. Konopacky in 1985 reported that in test streams 

 cold water temperatures, a lack of suitable substrate cover, and possibly food 

 size rather than food item density, caused underyearling salmon to migrate 

 downstream early in the fall. 



Evidence from several authors suggests that interstital spaces within stream 

 substrates may be a universal behavioral characteristic of salmonid fishes in 

 cold streams when overhead cover is lacking. Winter cover may be a primary 

 influence on the carrying capacity of trout in streams. 



In our study sections seasonal movements appear to be taking place. In 

 Martin Creek bull and westslope cutthroat trout seemed to move out of the section 

 between our marking run on September 11 and the recapture run on September 23, 

 1985. I also failed to observe any cutthroat in the upper section of Sand Basin 

 Creek by walking the banks on October 16, 1985, in contrast to many visual 

 sitings in August. A Forest Service field technician also reported observing a 

 tagged fish in the West Fork near the Sand Basin Creek road bridge; a section 

 that we did not tag fish in. This fish could have moved either upstream or 

 downstream from other sampling sections. Snorkel and mask work in the Bitterroot 

 drainage on 28 streams by O'Dell in 1984 and work by Wilson and Blount in 

 Rattlesnake Creek in 1985 have given the best local quantitative data on the 

 large seasonal changes in population density of cutthroat and bull trout in 

 specific stream sections. Both studies have shown large decreases in trout 

 populations during the fall, winter, and spring months compared with summer 

 abundance. The changes in trout population in these streams could be attributed 

 to movement out of the section, mortality, movement into the substrate, or 

 combinations of all the above. 



Our fishery study design appears to need a significant restructuring to 

 understand the dynamics of the fish populations we are trying to protect. Money 

 and man-power will probably be the most pressing need of a new study design. 

 Under current Department as well as U.S. Forest Service funding, not much more 

 than the existing effort is possible. 



