228 CONSERVATIOX DEPARTMENT 



Mayfly nymphs, it ^vill be noted, were the most abundant of the 

 available aquatic foods and formed ^^6.90 per cent of tlie total 

 number collected. Caddis larvae and pupae, while forming only 

 21.27 per cent of available foods of this ty])e, were eaten in the 

 greatest numbers forming 44.67 ])er cent of the lotal. In other 

 words, mayfly n3^m})hs while being the most available aquatic 

 food, were consumed second to caddis hirvae and pu|)ae. The 

 reasons for larger consumption by trout of a less available food 

 seem to lie in the foHowiug factors; viz.: the average size of may- 

 flies is much smaller than the average for caddis larvae and pupae 

 making tliem harder for ti'out to see; nuiyfly nym])hs live closely 

 attached to tlie rubble and gravel in swift water to avoid being 

 swept away by the current while the larvae of most caddisflies 

 live in conspicuous portable cases which they drag about with them 

 or in cases and shelters flxed to stones in prominent positions. 

 Also caddis pupae in order to emerge from the water and become 

 adults must leave their shelters and swim to the surface. During 

 this period, short as it may be, they are entirel}' unprotected and 

 at the mercy of any fish wdiichmay happen to see them. Examin- 

 ation of the 147 stomachs showed that a very large percentage 

 were eaten during this emergence period when the pupae were ris- 

 ing to the surface to take flight from 4he water as adults. Thus 

 wliile mayfly nymphs are numericalh' more available, actually they 

 are less available as shown by the numbers eaten b}^ the trout. 



Muttkowski* states that fish life in rapid streams is dependent 

 ii])on stoneflies for food. In the data presented here the stoneflies 

 form only 2.44 per cent of all consumed foods and 3.47 per cent 

 of aquatic consumed foods in the streams thus far studied in New 

 York State. Furthermore this food formed onh- 1.54 per cent of 

 the available drift foods and 14.67 per cent of the available aquatic 

 foods. 



Fly larvae and pupae may be counted a major trout food as this 

 group formed 13.84 per cent of available aquatic foods and 15.82 

 per cent of consumed aquatic foods. Beetle larvae, crayfish and 

 shrimps may be considered as minor foods as applied to the streams 

 and fish stomach examinations reported here. 



No aquatic vegetation was found in either the brown or brook 

 trout stomachs. However the rainbows were found to feed rather 

 consistently upon small amounts of the fresh water alga. 

 (Madophora. Metzelaart found vegetation in rainbow trout, 7-16 

 inches long to the extent of about 9 per cent by volume while in 

 larger rainbows, 17-28 inches long vegetation formed 17.8 per 

 cent of the stomach contents by volume. 



In last season's rei)ort a similar c()mi)aris()n of available and con- 

 sumed foods is made from twelve trout stomachs. Since that study 

 was based upon a few stomachs taken at one time it is hai'dly com- 

 parable with the data given here which is based upon 147 stonuichs 



* Muttkowski, Dr. Richard \. "The food of trout in Yellowstone National 

 Park." Roosevelt Wild Life Bulletin, Vol. 2, No. 4, pp. 470-407, Feb. 1925. 

 t Loc. eit 



