346 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



kinds were available to them and feeding con- 

 ditions were crowded. Consequently, more than 

 30 percent (5) of the grayling and 80 percent (4) of 

 the hybrid stomachs were empty. Fish eggs were 

 found in 8 of the 15 grayling sampled (table 27), 

 but the greatest number from any one specimen 

 was only 12. The fact that no sand or gravel ac- 

 companied these eggs demonstrated that they had 

 been taken while adrift and not while attached to 

 the substrate. 



Group S, Small trout from tributaries. — Seven 

 small trout were taken with a fine-meshed dip net 

 from Hatchery Creek at the time grayling fry were 

 descending. The smallest of these was 1.8 inches 

 in length and the largest, 3.4 inches (average, 2.3 

 ins.). These fish contained organisms common to 

 the stream as well as terrestrial insects that had 

 fallen into the water. There was no evidence of 

 cannibalism (table 28). 



Table 27. — Food of 13 grayling collected from Grebe Lake 

 tributaries during their spawning season, June 1954 



Table 28. — Stomach contents of 17 hybrid trout and 40 

 grayling from the Grebe Lake system, 1952 to 1954 



Food item 



Plecoptera 



Nymphs 



Ephemeroptera 



Nymphs 



Odonata nymphs 



Zygoptera 



Anisoptera 



Trlchoptera 



Larvae 



Diptera 



Larvae 



Pupae 



Hymenoptera 



Fish eggs 



Fish scales 



Food remains 



Total 

 number 



12 



129 



1 



37 



7 



Volumetric 

 compo- 

 sition 

 (Percent) 



2.3 



(') 



10.5 

 55.8 



(') 



7.0 



(') 



Frequency 

 of occur- 

 rence 

 (Percent) 



7.7 

 30.8 



46.2 



15.4 

 23.1 

 7.7 

 61.5 

 23.1 

 15.4 



1 Quantity in stomachs too little (less than 0.05 ml.) to be measured volu- 

 metrically. 



Group 4- Grayling and trout from Grebe Lake 

 proper. — Although competition for food was shown 

 by the contents of the stomachs from 40 grayling 

 and 10 trout captured in May, July, and August, 

 there was no evidence of predation between the 

 two kinds of fishes. Only two grayling stomachs 

 contained scales (table 28). The scales had 

 belonged to two grayling more than 9 inches long 

 and one trout over 8 inches; there was no trace of 

 flesh or bones. Diptera larvae and pupae were 

 the major food items in the group; these were 

 found in 70 percent of the trout and 72.5 percent 

 of the grayling. Fishes captured in Grebe Lake 

 when ice was present (May and June) were sub- 

 sisting primarily on amphipods and Diptera 



1 Quantity In stomach too little (less than 0.05 ml.) to be measured volu- 

 metrically. 



larvae. Later in the season (August) their diet 

 showed greater variety. Some individuals fed 

 primarily on damselfly nymphs, whereas many 

 others consumed mostly adult caddisflies. The 

 major portion of the diet consisted of Trichoptera 

 larvae in the early spring, and Ephemeroptera 

 nymphs in the late spring and summer. Tendi- 

 pedidae ( = Chironomidae) were also taken in great 

 numbers when available. 



Previous writers (Brown 1938a; Leonard 1939, 

 1940; and Rawson 1950) have also found that 

 insects, sometimes aquatic but at other times 

 terrestrial, predominate in the food of adult 

 grayling. Apparently the species feeds on what- 

 ever is available and shows no discernible 

 preferences. 



Although both the grayling and the hybrid 

 trout in Grebe Lake ingested the same types of 

 food items in approximately equal amounts, there 

 was no apparent antagonism between the two 



