Comparative Productivity of Colonizing and Low Abundance Coho Salmon Populations

Removal of migration barriers offers a promising strategy for conservation of Pacific salmon (Oncorhynchus spp.), but there are few examples of recolonizing population dynamics to guide selection and implementation of projects that improve habitat connectivity.  In this study, we used long term productivity data acquired via channel spanning weirs and smolt traps to address three crucial questions regarding recolonization and recovery of coho salmon (O. kisutch) populations in Washington State, USA.  First, what is the effect of increasing juvenile rearing, but not adult spawning, habitat?  We evaluated the change in productivity in the Bingham Creek watershed, where removal of an impassable screen in 1992 provided new access to a lake and its tributaries.  The newly accessible habitat has since been used extensively by juveniles but not adults.  Second, do colonizing populations have greater productivity than established populations, as would be expected under density-dependent population dynamics?  Productivity on the Cedar River, where a fish ladder constructed in 2003 granted access to 33 km of spawning and rearing habitat, was compared to that of established coho populations in Big Beef Creek and South Fork Skykomish River.  Finally, what governs the dynamics of populations at low abundances?  In this case, we determined the extent to which freshwater and/or marine processes have prevented recovery of the Deschutes River population following a precipitous abundance crash in the mid-1990s.  Overall, the goal of our research is to develop and advance predictive models of recolonization in order to maximize the benefit of limited funds for reconnecting previously isolated stream habitats.