BECKER: PARAMETERS OF JUVENILE CHINOOK SALMON 



menoptera, and Thysanoptera are almost en- 

 tirely of terrestrial origin, and other true 

 terrestrials occur among the adult Diptera, 

 Coleoptera, and Lepidoptera, other than the 

 Pyralidae (Table 1). The terrestrials were 

 probably seized while drifting, either sub- 

 merged or on the surface film. Since the river 

 drift of allochthonous insects contributed less 

 than 4% of the total food organisms by number, 

 they were of relatively low value to the diet 

 of juvenile chinook salmon in this study. 



Variability in Diet 



On a proportional basis, some differences 

 in food occurred between the six primary sta- 

 tions and some intersite influences were evi- 

 dent (Table 3). Adult midges were highly 

 utilized at Station D (70.1%), a shallow, semi- 

 enclosed backwater area with somewhat warmer 

 temperatures than other stations, but not larval 

 midges (6.1%). Noto)iecta nymphs were cap- 

 tured primarily at Stations A (7.3%) and 

 E (7.4% ), both with extensive areas of marginal 

 vegetation. Adult Hydropsyche were taken 

 primarily at Stations B (9.2%) and C (7.2%), 

 both with rubble substrates and partially ex- 



posed to flow of the main channel. Larval 

 caddisflies were captured primarily at Station 

 C (9.0% ). Collembola were taken most exten- 

 sively at Stations A (16.5%) and D (6.0%) 

 where extensive mud-water interfaces existed. 

 Proportional variations between stations were 

 probably influenced by numerous intersite fea- 

 tures including type of substrate, exposure 

 to current flow, changes in seasonal and regu- 

 lated water levels, and possibly feeding prefer- 

 ences of individual fish. 



Although juvenile chinook salmon at all 

 primary stations appeared to consume the 

 same general types of food. Table 3 indicates 

 some differences on the basis of relative pro- 

 portions. To explore these differences more 

 fully, the percentages of major food organisms 

 in seven categories (adult and larval Chiro- 

 nomidae, Hemiptera, adult and larval Hydro- 

 psychidae, Collembola, and "all other insects") 

 consumed within and between stations were 

 retabulated on a monthly basis. Additionally, 

 the samples were arbitrarily separated into 

 "upper" (A, B, C ) and "lower" (D, E, F) 

 stations because of the distance separating 

 them. Analysis by percent similarities (Whit- 

 taker and Fairbanks, 1958) was then applied 

 with the formula: 



Table 3. — Proportions of main insect groups utilized by juvenile chinook 

 salmon at six primary stations, combined 1969 data. 



' Includes all v^^inged forms, aquatic insects as well as terrestrials, plus Hemiptera 

 and Collembola. 



^ Includes larvae, pupae, nymphs, and other stages normally associated with benthic 

 substrates. 



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