THE ASSOCIATION BETWEEN CHANNEL GEOMORPHOLOGY AND SALMONID DISTRIBUTION IN NATAL HEADWATER STREAMS--THE RELATIONSHIP BETWEEN PHYSICS AND PHYSIOLOGY

Several species of anadramous and resident species of salmon and trout spend the first one to two years of their life in their natal streams growing to sufficient size to migrate to the ocean where they complete their growth to adulthood. Freshwater biologists have long observed that salmonids characteristically occupy stream locations that can be repetitively identified and classified as habitat types. A geomorphologist sees the same stream as a sequence of pools and riffles formed in relation to the gravel bars that result from the fluvial processing of watershed-generated sediment. The hydraulic processes responsible for sediment transport at high flows create repetitive bedforms that in turn determine the hydraulic characteristics of the water as it flows over and through them at lower flows. While salmonids are good swimmers, they tire relatively easily, and must find current velocities within their tolerance range. A careful documentation of hydraulic characteristics associated with bed morphology explains the observed distribution of juvenile fish, and morphologic characterization by channel surveys can be an effective quantitative measure of available living space.