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Occasionally both species were found utilizing the same areas. 

 The possibility that spatial segregation was occurring was 

 investigated by performing linear regression analysis on the 

 abundance of the two species in sub-sections where both species 

 occurred (Figure 22). Although the correlation was not 

 significant (r = -0.18, P > 0.05, d.f. = 54), the scatterplot 

 shows that there was a tendency for one of the species to be in 

 low numbers if the other species was in high numbers. 



The outcome of social interactions between brook trout and 

 Arctic grayling fry — such as spatial segregation — would probably 

 be dependent, in part, on the size difference between the two 

 species. Brook trout fry would normally be expected to have a 

 size advantage over grayling fry because they emerge between 

 February and April (Brown, 1971) , and are already one or two 

 months old by the time grayling emerge. In this study, the size 

 advantage of brook trout was quickly lost; by July 20-21 the 

 Arctic grayling were already longer than brook trout (Table 4, 

 Figure 3), and retained this size advantage until at least August 

 16-17, the last date the lengths of the two species were 

 compared. 



Predation of brook trout fry on Arctic grayling fry has been 

 reported by Nelson (1954) who found grayling fry in the stomachs 

 of 2-4-inch brook trout in Red Rocks Creek, Montana in late June. 

 The most likely time for predation to occur seems to be shortly 

 after emergence of grayling fry. The fry are very small during 

 this time (Lund [1974] found emigrating fry as small as 0.55 

 inches in the Red Rock River drainage, Montana) and the size 

 difference between the two species is at its greatest. The 

 possibility of predation was not investigated in this study. 



