|Abstract or Summary
- The behavior of two species of stream salmonids, juvenile coho salmon, Oncorhynchus kisutch (Walbaurn) and cutthroat trout, Salmo clarki clarki Richardson, was studied in terms of the time spent by individual fish in carrying out various activities. Studies were conducted from June 1968, through May 1969, at Berry Creek, a small woodland stream located approximately ten miles north of Corvallis, Oregon. A 1500 foot section of the stream was brought under complete flow control for experimental purposes by a concrete diversion dam and a bypass channel. Water flow into the experimental section was controlled by a large gate valve at the dam. The lower part of the controlled section was divided into experimental sections that were separated by inclined-screen fish traps. The Berry Creek Experimental Stream Laboratory is maintained as a field research station by the Department of Fisheries and Wildlife, Oregon State University. Behavioral observations were made from an observation booth located in an experimental section of Berry Creek. Time-budget analyses derived from observational data were used to evaluate the effects on production of the interaction between individual salmon stocked at different densities in separate stream sections and the interaction among populations comprising both species stocked separately and together at similar densities in different sections of the stream. The growth rates of juvenile coho salmon stocked during June and July 1968, at different biomasses in five of the experimental sections generally declined with increases of salmon biomass. Downstream movement and mean percentages of time spent in agonistic behavior by individual salmon increased with increases in biomass. Higher values of production and mean biomass were generally recorded for an experimental group comprising salmon and trout than for single species groups. Several of the trout on occasion occupied the riffle area of the observation section, whereas, coho salmon remained in the pool throughout the experiment. The use of the riffle area by the trout may have resulted in more efficient utilization of space and food and may explain, in part, the differences in production between the trout-salmon group and the single species group. The growth and location in the stream section of an individual trout or salmon appeared to depend on the fish's position in the integrated social structure. Fish of high social position benefitted in terms of increased amounts of feeding time, decreased activity and decreased agonistic behavior as compared with fish of lower social position. The effect of intraspecific interaction among salmon appeared to be greatest at those stocking densities which resulted in a decline of growth rate from the growth rates that were associated with the highest values of production. This interaction appeared to lead to a compromise between energy expenditures for agonistic behavior and efficient metabolism that resulted in stock densities between two and three grams/meter2 of section area.