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A 4°C temperature differential was maintained between two model streams. Steelhead trout (Salmo gairdneri) were introduced as embryos and retained for one year. The following year, steelhead and coho salmon (Oncorhynchus kisutch) were introduced as embryos and retained together. Macroinvertebrates and fish were sampled every three weeks. Primary production and respiration were estimated seasonally.
Prey biomass and diversity, and the production, biomass, and numbers of steelhead and coho were generally lower in the heated stream than in the control stream. Production, biomass, and numbers of steelhead were lower than those of coho and lower when coho were present than when they were absent. It was concluded (1) that moderate temperature elevation can decrease the productivity of streams for steelhead and coho when food is limited, (2) that coho might reduce the productivity of streams for steelhead more than temperature elevation might, and (3) that model stream results are more likely to corroborate single-species bioassays of fish fed limited rations than of fish fed to repletion.
temperature, competition, production, productivity, model streams, microcosms, benthos, periphyton, salmonids
Section Supervisor, Northrop Services, Inc., Corvallis, OR
Fishery Biologist, U.S. Fish and Wildlife Service, Portland, OR