High percentages of fine particles in the substrate have 

 been shown to have a negative effect on salmonid eggs and fry 

 (Hausle and Coble 1976; Phillips et al. 1975). Hausle and Coble 

 (1976) found that sand inhibited the emergence of brook trout, 

 but emergence was still between 80 and 90% when 20% of the 

 spawning substrate was composed of sand (the highest percentage 

 at any of the Big Hole spawning sites) . However, Phillips, et 

 al., (1975) found that mean survival to emergence of coho salmon 

 ( Onchorhynchus kisutch ) and steelhead (O. mykiss ) fry was roughly 

 70% when sand made up 20% of the substrate. If grayling are 

 similarly affected, the 20% sand in the Big Hole substrate may be 

 lowering fry emergence by 10 to 30%. 



However, several studies dealing with grayling (Scott and 

 Crossman 1973; Nelson 1954; and Bishop 1971) have indicated that 

 grayling will spawn over a wide variety of substrates ranging 

 from boulders to sand. Because grayling do not build redds 

 (Scott and Crossman 1973) , substrate composition may not be an 

 extremely important variable in determining spawning success. 



There appears to be little or no correlation (R 2 ) between 

 substrate composition and the numbers of YOY at or near the 

 spawning sites (Table 10) . There is little correlation between 

 YOY grayling numbers and the percentage of gravel in the 

 substrate, where 28% of the variation in YOY grayling numbers is 

 attributed to the percentage of substrate gravel. 



There are several possible reasons for these low 

 correlations. First, selection of spawning substrate by grayling 



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