The nature of the interaction between juvenile coho salmon, Oncorhynchus kisutch (Walbaum), and fall chinook salmon, 0. tshawytscha (Walbaum), was studied in Sixes River, Oregon. Seining, snorkeling, and tagging were used to determine distribution and patterns of growth of these two species in the stream environment. Experiments conducted in flowing-water observation troughs that provided volitional residence were designed to examine the outcome of agonistic behavior between these two species. Both species were distributed throughout the entire river system in early spring. During this period, underwater surveys in the main river and selected tributaries indicated that both species preferred the same habitat. As temperatures increased during the late spring, coho disappeared from the main river, but continued to occupy cool tributaries. Fall chinook, on the other hand, were found primarily in the main river until early summer, when they moved to the estuary. Relatively few individuals remained in the tributaries. Experiments conducted in the troughs revealed that agonistic behavior, including nipping, chasing, lateral display, submission, and fleeing, occurred between juvenile coho and fall chinook. When the two species were together in the troughs and in cool tributary streams, coho grew faster than chinook. When isolated in troughs, both grew at similar rates. Coho tolerated fewer individuals per unit area than did chinook, and occupied positions of dominance near the source of incoming food at the upstream end of the troughs. Coho had brighter fin and body colors, greater fin development, deeper bodies, and were heavier than fall chinook of the same length. Coloration and morphology appeared to be important factors influencing the "apparent" size and presumably the social status of both species. Juvenile coho, with extensive development of fins and coloration and intense territorial behavior, are hypothesized to be adapted to small, cool tributary streams. Fall chinook, on the other hand, with conservative development of fins and coloration and related behavior patterns, appear to be adapted to conditions in the main river and estuary.

Every year, countless juvenile Pacific salmon leave streams and rivers on their migration to feeding grounds in the North Pacific Ocean and the Bering Sea. After periods ranging from a few months to several years, adult salmon enter rivers along the coasts of Asia and North America to spawn and complete their life cycle. Within this general outline, various life history patterns, both among and within species, involve diverse ways of exploiting freshwater, estuarine, and marine habitats. There are seven species of Pacific salmon. Five (coho, chinook chum, pink, and sockeye) occur in both North America and Asia. Their complex life histories and spectacular migrations have long fascinated biologists and amateurs alike. Physiological Ecology of Pacific Salmon provides comprehensive reviews by leading researchers of the physiological adaptations that allow Pacific Salmon to sustain themselves in the diverse environments in which they live. It begins with an analysis of energy expenditure and continues with reviews of locomotion, growth, feeding, and nutrition. Subsequent chapters deal with osmotic adjustments enabling the passage between fresh and salt water, nitrogen excretion and regulation of acid-base balance, circulation and gas transfer, and finally, responses to stress. This thorough and authoritative volume will be a valuable reference for students and researchers of biology and fisheries science as they seek to understand the environmental requirements for the perpetuation of these unique and valuable species.