GRAYLING OF GREBE LAKE 



345 



Table 26. — Average number of each kind of food organism (and ptrcentage frequency of occurrence) in grayling of age-groups 



and I, Grebe Lake, 1954 



Food items in these fish were decomposed and could not be enumerated. 



Four principal groups of fishes were sampled for 

 food content: (1) young-of-the-year and 1 -year- 

 old grayling collected at intervals throughout 

 1954; (2) spawning females of grayling and of 

 hybrid trout; (3) small trout (less than 3.4 ins. in 

 length) inhabiting Hatchery Creek during the 

 time the newly hatched grayling fry were descend- 

 ing in July 1953; and, (4) adults of both species 

 taken from the lake proper during the 1952 to 

 1954 seasons. 



Group 1. Grayling belonging to age-groups and 

 I, collected throughout the 1954 season. — Grayling 

 in this group were taken by seining the shore of 

 Grebe Lake at intervals between July 2 and Sep- 

 tember 1, 1954. Of all the fish in each collection, 

 only the five that were nearest the mean length 

 in each lot were used in the food analysis. 



Young of the grayling start to feed early in life. 

 Some individuals in a group of hatchery-reared 

 fry began ingesting food on their fourth day and 

 by the eighth day all individuals sampled con- 

 tained food (Brown 1939). The yolk sacs of those 

 that Brown measured averaged 0.3 inches when 

 food was first consumed and had disappeared in 

 most fish by the end of the second week. The 

 smallest specimen that I found with food in it in 

 Grebe Lake (July 2, 1954) had a yolk sac 0.1 -inch 

 in length and was probably between 1 and 2 weeks 

 old. In this body of water, young grayling (to 1.5 



inches total length) subsisted primarily on Daphnia 

 and on Diptera larvae and pupae (table 26), or- 

 ganisms that are especially abundant in the shoal 

 areas of Grebe Lake, which is inhabited by these 

 small fish. Stomachs collected between July 12 

 and August 6 contained only Daphnia. From 

 August 6 to September 1, young fish consumed 

 mainly ephemerids (mostly Callibaetis) along with 

 lesser amounts of Tendipedidae ( = Chironomidae) 

 larvae and pupae, Gammarus, Daphnia, and Cy- 

 clops. Winged insects (adult Diptera) first ap- 

 peared in the diets on August 16. 



The 1-year-olds collected in the spring and early 

 summer of 1954 had eaten not only a more varied 

 diet, but also were taking larger organisms than 

 were the young-of-the-year. Among the food 

 items were some Trichoptera and relatively more 

 gammarids. The first terrestrial insects were 

 found in stomachs on June 26 from fish averaging 

 4.3 inches total length. By July 18 the variety of 

 food found in the stomachs of the 1-year-olds was 

 nearly the same as that consumed by older fish 

 (exceptions were the large Odonata of a size too 

 great to be ingested by small fish) . 



Group 2. Spawning female trout and grayling. — 

 Stomachs of 13 grayling and 5 hybrid trout were 

 obtained from spawning adults collected in the 

 streams tributary to Grebe Lake. Although these 

 fishes readily took food in these streams, very few 



