Defining Fish Habitat from a Geomorphic Perspective

The conservation and restoration of freshwater habitat is essential for effective management of Pacific salmon. Improving our understanding of fish-habitat relationships will facilitate the identification of valuable and degraded freshwater habitats. Here we use a habitat classification scheme grounded in fluvial geomorphology to quantify salmon habitat in the Wenatchee River watershed. We couple this classification scheme with historical and contemporary datasets to estimate the potential and current availability of salmon habitat throughout the watershed. Our aim is to locate where habitat loss has occurred in the watershed and translate habitat loss into changes in salmon production capacity. For example, we estimate the current availability of pool habitat in Wenatchee River tributaries is 23% less than what the tributaries can potentially provide. Our analyses indicate that a significant reduction in large wood abundance may be contributing to losses in tributary pool habitat, and as a consequence juvenile Chinook production capacity from Wenatchee River tributaries has been reduced by approximately 10%. This study expands a framework for identifying mechanistic linkages of habitat loss while providing robust estimates of habitat availability and salmon production capacity at spatial scales relevant to salmon populations and fisheries management.