Biological Survey — Oswego Watershed 



203 



pools compensate somewhat for the lack of available bottom foods 

 in pools. 



93.48% of all the forage organisms taken in pool drift were ter- 

 restrial in origin, the remaining 6.52% aquatic in origin. It is 

 interesting to note the close correlation between percentages of 

 aquatic and terrestrial food in stream drift and pool drift. In 

 the former, 6.98% was aquatic and 93.02%. was terrestrial. In 

 the latter 6.52% aquatic, and 93.48%; terrestrial, slightly less of 

 the organisms being aquatic in origin in pool drift. 



Comparison of Total Available Food and Food Actually 

 Eaten by Trout. — An angler permitted us to remove the stomachs 

 from twelve brook trout he had caught in the same section of the 

 stream (station 15) in which drift and bottom studies were being 

 made. Examination of the food found in these stomachs corre- 

 lated with data on total avadable food permits this comparison. 



Table 7 shows that the trout had largely eaten of the most availa- 

 ble type food, the aquatic. More than 83% of the food found in the 

 twelve stomachs was aquatic in origin, i. e., it was food indige- 

 nous to and grown in the stream itself. The remaining 17% was 

 terrestrial in origin, i. e., adult animals, non-gill-bearing and non- 

 aquatic, which had probably fallen into the water accidentally. 

 As taken in the drift net catches here, the latter type of food formed 

 only .7% of all available foods. Insects formed 61% of the diet 

 of the trout and formed 59.93% of all available foods. Crayfish 



Table 7. 



Summary of Total Available Food and Food Actually Eaten 

 by Trout 





Type of food 



Total 



available 



foods 



Foods 

 con- 

 sumed 



A. 



As to origin: 



Aquatic 



99.3 



.7* 



83% 



17% 





Terrestrial 



As to classes of foods: 



Insects 





100% 



100% 



B. 



59.93 

 40.07 



61% 



32% 

 7% 





Crayfish and shrimp 



Worms and millipedes 



As to origin of insects: 



Aquatic 





100% 



100% 



C. 



99.3 



.7. 



50% 

 11% 





Terrestrial 





100% 



61% 



* Foods listed in the above table as being "terrestrial", can all properly be 

 termed "drift food." 



