Flows 



Streamflow discharges were much higher in the upper Big Hole 

 River drainage during the summer of 1989 than they were the previous 

 summer. Figures 12 through 15 present the range of flows recorded at 

 each of four staff gauge sites with 95% confidence limits. 



Stomach Content Analysis 



Arctic grayling in the Big Hole River and its tributaries appear 

 to select different types of food items than the brook trout in the 

 same areas during the summer months. Grayling between 6 and 10 inches 

 (N=9) had stomach contents consisting of 32% mayflies by volume while 

 brook trout of the same size (N=30) showed 23% of their contents to be 

 made up of a variety of fish (Fig. 16) . Grayling also tended to 

 utilize other organisms present on the water surface, such as stonefly 

 adults and terrestrial insects, in much greater proportion than did 

 brook trout. Larger grayling (>10") (N=3) showed a more dramatic 

 preference for surface food items (adult mayflies, caddisflies, 

 stoneflies, and terrestrial insects) than did similarly sized brook 

 trout (N=5; Fig. 17) . Subsurface food items such as fish, leeches, 

 and cranefly larva comprised the majority of the diets of larger brook 

 trout. 



Arctic grayling in the upper Big Hole River drainage seem to show 

 a strong preference for surface food items while brook trout consume a 

 larger proportion of subsurface items, indicating that there may be 

 little direct competition for food between the two species during the 

 summer months. This situation may change considerably during the 

 winter months when surface food items probably become less available. 

 Of the fish found in stomachs of brook trout none could be positively 

 identified as grayling fry or YOY. The majority of the fish present 

 in the stomach samples 



31 



