Salmonid influences on rivers: A geomorphic fish tail

Studies of the effects of salmonids on the environment have focused primarily on the biological linkages between salmon runs and stream ecology. Less effort has focused on geomorphic effects. A review of the literature indicates potential (i) direct effects in response to mass spawning of salmonids, including changes in streambed and bank morphology and annual volumes of bedload transported; and (ii) indirect effects including supply of nutrients to the riparian zone, which may influence the in-channel dynamics of large woody debris and bank stability, and effects on population density of net-spinning caddisfly larvae which may influence streambed stability in finer gravel substrates. More research is needed over long time frames, however, to ascertain whether such effects are geomorphically significant at larger spatial and longer temporal scales, and to estimate the sizes of populations required to cause geomorphically significant responses. Some possible studies are suggested.