PRODUCTION OF JUVENILE CHINOOK SALMON, 

 ONCORHYNCHUS TSHA WYTSCHA, IN A HEATED MODEL STREAM^ 



Peter A. Bisson-and Gerald E. Davis' 



ABSTRACT 



Temperature was elevated approximately 4°C in a model stream, compared with an unheated but 

 otherwise similar control stream. The streams were located outdoors and received identical amounts of 

 exchange water from a nearby creek. Diel and seasonal temperature fluctuations were similar to those 

 of area streams. Juvenile spring chinook salmon, Oncorhynchus tshawytscha, were introduced into each 

 stream either as eyed eggs or fry and allowed to remain for approximately 1 yr. Two consecutive year 

 classes of juvenile salmon were studied. Their production was measured triweekly and related to 

 changes in temperature, food availability, and other environmental factors. Ancillary experiments 

 utilizing water from the model streams permitted measurement of diflferences in growth rate of salmon 

 fed various rations. 



Salmon production in the control stream exceeded that in the heated stream. In 1972, total production 

 in the control stream was twofold greater and, in 1973, it was approximately 30% greater than in the 

 heated stream. Elevated temperature resulted in reduced growth rates of the fish especially as food 

 became less abundant and at times also resulted in lower biomasses of food organisms, either because 

 the temperature increase directly affected survival and growth of benthic invertebrates or because 

 increased sedimentation associated with heavier growth of filamentous algae made riffle substrate less 

 suitable for certain species. Beneficial effects of increased temperature appeared to include protection 

 from infestation by a trematode parasite (Nanophyetus salmincola) and, possibly, increased tendencies 

 of some invertebrates to enter the drift. 



Studies of the effects of elevated temperature on 

 stream dwelling organisms have been largely 

 confined to short-term laboratory experiments or 

 to field surveys associated vi^ith man-caused ther- 

 mal increases. We have employed two large model 

 streams, one heated and one unheated, to examine 

 the effects of constantly elevated temperature on 

 production of juvenile chinook salmon, Oncorhyn- 

 chus tshawytscha (Walbaum), under conditions 

 similar to natural streams, but where temperature 

 could be controlled. Identifying the factors 

 governing productivity of the streams that were 

 influenced by increased temperature and measur- 

 ing the impact of the addition of a known amount 

 of heat on chinook salmon production were the two 

 main objectives of the research. 



Temperature change can affect salmonid fishes 

 in two general ways. First are the direct effects, 

 e.g., accelerated developmental rates, altered food 

 conversion efficiencies, and, under certain condi- 



'Technical Paper No. 4078, Oregon Agricultural Experiment 

 Station, Oregon State University, Corvallis, OR 97331. 



-Department of Fisheries and Wildlife, Oregon State Univer- 

 sity, Corvallis, OR 97331; present address: Weyerhaeuser Com- 

 pany, Longview, WA 98632. 



•"Department of Fisheries and Wildlife, Oregon State Univer- 

 sity, Corvallis, OR 97331. 



tions, lethality. These kinds of effects have 

 received considerable attention in laboratory 

 experiments. Less well understood are the indirect 

 effects, one of the most important being resultant 

 changes in the abundance of food organisms. In a 

 previous study involving the same streams, Iver- 

 son (1972) found that the production of juvenile 

 coho salmon, 0. kisutch, was significantly reduced 

 in the heated stream compared with the unheated 

 control, and he attributed this reduction mainly to 

 lower biomasses of immature stages of insects in 

 the heated stream. Evaluating the importance of 

 indirect consequences of temperature elevation on 

 juvenile chinook thus became one of our major 

 concerns, for water quality guidelines relating to 

 the temperature requirements of salmon and trout 

 are based primarily upon knowledge of direct 

 effects and to a much lesser extent upon possible 

 indirect or secondary effects. 



MATERIALS AND METHODS 



Physical Characteristics of the Streams 



The model streams were located at the Oak 

 Creek Laboratory of Biology near Corvallis in 



Manuscript accepted April 1976. 



FISHERY BULLETIN: VOL. 74, NO. 4, 1976. 



763 



