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 Microhabitat Utilization 



Depth and Velocity 



Young-of-the-year Arctic grayling were captured at depths 

 ranging from 0.2 to 3.0 ft in water with velocities ranging from 

 0.0 to 1.87 ft/s (Figures 5 and 6, Table 6). Depths and 

 velocities falling within the range of the utilization index 

 value of 1.0 were 0.5 to 1.3 ft and 0.18 to 0.84 ft/s, 

 respectively. These ranges may not accurately reflect the 

 preferences of the fish, because the preferred depths and 

 velocities may not be present or may be in short supply. 

 Preference is typically thought to be exhibited when a particular 

 habitat variable is utilized with a frequency that is greater 

 than its relative availability (Bovee 1986) . An unbiased 

 determination of habitat availability is possible only if a 

 sampling approach is used that provides for variables to be 

 measured in all habitat types (pools, riffles, backwater areas, 

 side channels, etc.) throughout the entire Study Area and in 

 proportion to the frequency of occurrence of those habitat types. 

 This sampling approach was not employed in this study and 

 accurate determinations of preference are therefore not possible. 

 However, habitat variables were measured along 50 transects that 

 went through or near to capture sites, and frequency analysis of 

 these data were used to provide a rough idea of the availability 

 of depths and velocities in areas close to the capture sites. 

 Results show that depths and velocities within the 1.0 index 

 range were 0.3 to 0.8 ft and 0.0 to 0.65 ft/s, respectively 

 (Figures 7 and 8, Table 6). Compared to the utilization data, 

 this is somewhat slower and shallower water, and suggests that, 

 within the areas close to capture sites, the fish are 

 preferentially selecting for the faster and deeper areas. 



A significant limitation in the availability database is 

 that, for the most part, it does not include pool habitats, 

 because few YOY fish were found in or near these habitat types. 

 If estimates of conditions in the pools (righthand column in 

 Table 6) are also considered, there will probably be a relative 

 increase in the amount of deeper water available to the fish 

 (water is mostly from 1-4+ ft deep) and a relative decrease in 

 the amount of available fast water (most water in pools has 

 little or no current) . This tends to support the hypothesis that 

 the fish are selecting for faster water, but would suggest that 

 deeper water is not being selected preferentially. One possible 

 explanation for why the fish seem to be selecting for deeper 

 water in the areas near capture sites, but not in the pools, 

 could be the threat of predation by large brook trout in the 

 pools. If the YOY Arctic grayling are avoiding the pools for 

 this reason, then this habitat type may not truly be "available" 

 in the sense that the fish are not free to select those areas, 

 unencumbered by predation. Another possible explanation could be 

 that the fish are avoiding the pools because there is 



