Salmonids and the Hydrologic and Geomorphic Features of Their Spawning Streams in British Columbia

The objective of this chapter is to describe some key linkages between the ecology of salmonid fish and the hydrologic and geomorphic features of their spawning streams in British Columbia. Salmonid refers to all species in the Salmonidae family of fishes, which includes Pacific salmon and trout (Oncorhynchus spp.), char (Salvelinus spp.), grayling (Thymallus spp.), whitefish and cisco (Coregonus spp.), Atlantic salmon and trout (Salmo spp.), inconnu (Stenodus spp.), and round whitefish (Prosopium spp.). The focus here is on Pacific salmon, trout, and char because of their widespread distribution in the province, their extensive use of stream habitats for spawning, and the volume of research devoted to these socio-economically important species. Stream-spawning salmonids and their reproductive success are affected by the hydrologic and geomorphic watershed processes that define and shape their streams and spawning habitats. To manage fish and land-use practices effectively, we need to understand how salmonid ecology and physical stream processes interact and are altered by natural and human disturbances in their watersheds. The dependence of stream organisms on the quantity, quality, and movement of flowing waters has always been part of the underlying fabric of stream ecology. In the 35+ years since Hynes published his landmark book, The Ecology of Running Waters (Hynes 972), appreciation for these hydrologic–biologic linkages has advanced considerably in North America, driven largely by the environmental movement and our increasing concern over the effects of land and water uses on fish and their habitat. Our understanding of specific ecological–hydrological processes and interactions in stream systems has progressed significantly. For example, we now recognize the ecological significance of hyporheic zones (See Chapter 3, “Stream and Riparian Ecology”) where ground and surface waters mix below the streambed surface, creating important habitats for faunal communities (Edwards 998). We also now recognize many of the dynamic and hydrologically mediated biochemical exchange processes that determine how nutrients and organic matter “spiral” downstream and are transformed and moved through stream ecosystems (Newbold et al. 982). Woody debris is no longer “cleaned” from streams because it has been shown to be a critical physical element for stream morphology, fish and invertebrate habitats, and other important ecological functions (Bisson et al. 987). These advances in our knowledge have helped us better appreciate the importance of hydrologic and geomorphic processes to stream ecosystems and have aided in the development of more effective water and stream management policies. Nevertheless, significant gaps still exist in our knowledge of stream and watershed processes and of human impacts on the hydrology, morphology, and ecology of streams (Young 2000; Rosenau and Angelo 2003; Moola et Salmonids and the Hydrologic and Geomorphic Features of Their Spawning Streams in British Columbia Chapter 4