A STUDY OF TWIN L.\KE.S, COLORADO. 



169 



SUMMARY AND DISCUSSION OF RESULTS. 



The following table shows the average per cent of the different elements com- 

 posing the stomach contents of all the trout examined. The percentages given for 

 each species were obtained b^' dividing the sum of the per cents of the different food 

 elements bv the number of stomachs containing food. 



Twenty-two item> appear in tlie al)ovc tal>ic. and all e.xccjjt one (.^and and gravel) 

 ma}- bo regarded as sources of nourishment. While much of the \egctable iiuitter 

 had no food value and was probably taken largely by accident, still, in a considerable 

 number of cases, it was digestible material which would afford nouri.shment, and was 

 present in such quantities as to indicate that it had been eaten purposely. 



The table shows that there was considerable difference in the diet of the different 

 species. The landlocked salmon (Salni.n .whr/go) had partaken of 12 out of the 21 

 items of food; the greenback trout {S. Kfomia.s) 12; the rainbow trout (S. irideus 

 sJuuta) 17; small brook trout {Salndlnux fontinalh) li_»; and large brook trout 16. 

 Thus the rainbow had the greatest variety in its diet. 



The mammal remains consisted chiefly of the bones of a small nianimal. appar- 

 ently a mouse, e.iten by a rainbow trout. 



These four species of trout differed very widely in the relative amount of lish 

 consumed. The landlocked salmon had partaken most freely, tish remains constitu- 

 ting an average of more than 1-third of the stomach contents; the rain))ow trout 

 ranked second in this respect; while the brook trout had eaten most sparingly of this 

 kind of food. It is interesting to note in this connection, however, that all tlie tish 

 remains that could l)e identiffed were found to be young suckers. 



Tile last table shows how important insects are in the food of these trout during 

 the summer. On an average, they constituted 40.9 per cent of all the material found 

 in the stomachs of landlocked salmon; 71.5 per cent in greenback trout; 50.1 in rain- 

 bow trout; HD.ti in the small In-ook trout; and 58.6 in the large brook trout. The fry 

 that were examined were entirely dependent on insects for their food. With the 

 exception of the small brook trout and the fry, the insect material found in the 



