BISSON and DAVIS: PRODUCTION OF JUVENILE CHINOOK SALMON 



due to their being cold-adapted species. No large 

 scale mortality of larvae or pupae was detected in 

 the heated stream, even during summer months. 

 However, very early developmental stages and life 

 history patterns may have been altered (Macan 

 1961a, b; Hynes 1970). 



The tendency of certain invertebrates in the 

 heated stream to enter the drift in greater 

 proportion to their benthic biomasses (Table 3) 

 was probably related both to elevated temperature 

 and to fine sediment levels. Increased drift as- 

 sociated with increasing temperature was de- 

 scribed for certain invertebrates by Miiller (1963), 

 Waters (1968), and Pearson and Franklin (1968). In 

 other studies, significant positive correlations 

 between drift and temperature have not been 

 detected (Bishop and Hynes 1969; Wojtalik and 

 Waters 1970; Muller 1970; Reisen and Prins 1972). 

 Experimental additions of sediments to a stream 

 were found by Rosenberg and Weins (1975) to 

 significantly increase the drift of some inverte- 

 brate taxa and to have inconsistent effects on 



others. 



Although the influence of elevated temperature 

 on the production of juvenile chinook salmon was 

 complex, we were able to identify both beneficial 

 and harmful effects. The fish benefited in several 

 ways. First, the temperature increase may have 

 stimulated higher consumption rates when suit- 

 able food was very abundant, although this con- 

 dition was rarely achieved. Second, higher temper- 

 atures afforded protection from infestation by a 

 trematode parasite, which heavily infested the 

 majority of individuals in the control stream. 

 Third, certain invertebrates may have been 

 stimulated to enter the drift and thus became 

 more available as food. Fish were harmed in at 

 least two ways. First, growth efficiencies were 

 lowered at all but the highest consumption levels. 

 Second, despite high drift ratios of some taxa, food 

 availability was generally reduced because 

 preferred food organisms were much less abun- 

 dant in the substrate of the heated stream than in 

 the control. The net result was that salmon 

 production in the heated stream was about 50% 

 less in 1972 and 25% less in 1973 compared with the 

 unheated stream. 



ACKNOWLEDGMENTS 



Support for the study was provided by the Office 

 of Water Research and Technology, U.S. Depart- 

 ment of Interior, under provisions of Public Law 



88-379. C. E. Warren, C. B. Schreck, N. H. Ander- 

 son, and C. D. Mclntire offered suggestions for the 

 manuscript, and C. D. Mclntire and H. K. Phinney 

 aided in identifying stream flora. David Neiss, 

 Tim Joyce, Howard Worley, John Toman, Steve 

 Ross, Eric Johansen, Jean McRae, and Mary 

 Buckman assisted with field and analytical work. 



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