14 



the streams was in terms of amount of solid overhead concealment cover for 

 trout — cover submerged in the stream or within a few centimeters above the 

 water surface. Averaged over all 30 study stations, control areas had 60% more 

 such cover than did urban areas — 8.33% vs 5.22%, a difference significant at 

 the 97.5% confidence level (Table 2). For Bozeman Creek alone, the difference 

 was even more pronounced. Urban areas contained especially low amounts of cover, 

 slightly less than 1%, and the control areas did not have particularly high 

 amounts, 5.3%, but this was a several-fold difference or 485% more in control 

 areas, a difference significant at the 99.8% level. 



It can be inferred that reduction of instream concealment cover is a major 

 impact of urbanization along trout streams of the types included in our study. 

 Wells (1977) also found that cover reduction was strongly associated with 

 channel straightening in another stream near Bozeman, although that was not a 

 consequence of urbanization. 



The only other measured habitat variables having significant urban-vs-control 

 differences at the 90% confidence level or higher were channel width, which 

 was narrower in urban areas (96.3% confidence level), and amount of eroding 

 bank — 34% in urban areas vs 23% in control areas, a difference of 48% relative 

 to the control figure and significant at the 90% confidence level (Table 2). 



Part of the difference in channel width could be an artifact of the 

 longitudinal distribution of study stations within the stream systems. This 

 possible effect has not yet been analysed. However, we suspect that encroach- 

 ment on the channel by land fill involved in urban development may have been a 

 major influence in narrowing the urban stream sections. 



The higher degree of bank erosion in urban areas may represent decreased 



