A STUDY OF TWIN LAKES, COLORADO. 



169 



SUMMARY AND DISCUSSION OK RESULTS. 



The following table shows the average per eent of the different elements coin- 

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

 each species were obtained by dividing the sum of the per cents of the different food 

 elements by the number of stomachs containing food. 



Land- 

 locked 

 salmon. 



Green- 

 back 

 trout. 



Rainbow 

 trout. 



Small Large 

 brook brook 



trout. trout. 



Fry. 



Mammal remains 



Fish remains 



Araneida [spidersj 



Hydrachnidse (water-mites 



Ephemeridti 



Oaonata 



1'1< ptera 



t »rthoptera 



Hemiptera 



Neuroptera 



Trichoptera 



Lepidoptera 



Dlptera 



i Imronomus I larrse, pup 



simuliuiu (larvse) 



Coleoptera 



Hymenoptera 



[nseel fragments 



Crustacea 



Mollusca 



\ egi i.ii'i-- debris 



Sand and gravel 



16 -1 



4. -10 



5.55 

 .20 



10.00 

 2.11 



.11 



15.31 







1.51 



.27 



.06 



13.05 



.it; 

 g 20 

 l:: 95 

 2.80 



0.04 

 !l 

 .10 





.12 



.'.'7 



.13 

 3. a. 



1.17 



1.9M 

 7. 75 

 1.18 

 31 70 

 .i. 62 

 .38 

 8.70 

 7. 17 



86 



Loo 



.69 

 11 60 

 7 60 

 6. 18 



.17 



'is I M 



IS 

 B0 

 16 



.87 

 .16 



.7-J 

 1. is 

 'J. mi 



5. I" 



9 l . 



.07 

 •_'. 17 





8.20 



11.40 



I. I" 



Twent y-t wo ii •'.!{• appear in the above table, ;m<l all except one (sand and gravel) 

 may be regarded as sources of nourishment. While much of the vegetable matter 

 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 nourishment, and was 

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



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

 species. The landlocked salmon (Salmo sebago) had partaken of 1- mil of the 21 

 items of food: the greenback trout (S. stomias) \'2\ the rainbow trout (.v. irideus 

 shasta) 17; small brook trout (Salvelinus fontinalis) 10; and lai'ge brook trout L6. 

 Thus thi' rainbow had the greatest variety in its diet. 



The mammal remains consisted chiefly of the bones "1' a small mammal, appar- 

 ently a mouse, eaten by a rainbow trout. 



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

 consumed. The landlocked salmon hail partaken most freely, fish remains constitu- 

 ting an average of more than 1-third of the stomach contents; the rainbow 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 t lie fish 

 remains that could be identified were found to be young suckers. 



The 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 percent in greenback trout ; 50.1 in rain- 

 bow trout ; 99.6 in the small brook 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 



