Structure, dynamics, and persistence of Chinook salmon in the Frank Church River of No Return Wilderness

Background/Question/Methods

North American landscapes are often extensive, and prone to natural and anthropogenic disturbances. To persist in these dynamic systems, native aquatic species have developed diverse life history strategies that utilize a broad range of habitats across time and space. Consequently, effective conservation and restoration strategies for at-risk species require information collected at appropriate spatial and temporal scales. Within the Middle Fork Salmon River (MFSR), we are developing long-term data sets across large spatial scales to describe biological and physical processes. These data are advancing knowledge of the landscape and local biophysical conditions and processes that influence aquatic habitat, and the distribution, diversity, and persistence of salmon. The MFSR drains a remote area of central Idaho and for most of its length, flows through remote wilderness that provides critical habitat for six ESA listed species. The study area is unique because: a.) Chinook salmon are wild and indigenous, b.) natural processes such as fires, floods, and debris flows maintain a dynamic mosaic of habitats, and c.) the abundance of ESA-listed, Chinook salmon has been monitored annually for 56 years. We have supplemented this rare dataset with a comprehensive, spatially continuous redd census throughout the full stream network and a landscape-level description of salmon genetic structure. These biological data are being integrated with basin-scale predictions of salmon spawning habitat distributions, estimates of sediment motion and bedload transport, mapping of recent fires and debris flows, basin-scale patterns of spatial autocorrelation in water temperatures, and continuous remote sensing of selected stream channels via airborne laser altimetry.

Results/Conclusions

We describe how these unique data sets are informing a host of studies including: validating methodologies and sampling designs for population monitoring; examining linkages between fine scale genetic structure, demographic parameters, and environmental characteristics; assessing  dispersal and environmental constraints using spatial autocorrelation; validating hydrologic models that predict spawning gravel distribution; monitoring salmon responses to stochastic events, assessing environmental covariates affecting salmon habitat occupancy, and evaluating changes in salmon phenology in response to a changing climate. Our results emphasize the importance of maintaining habitats with high densities of individuals, but also suggest that broad views are needed to accommodate the dynamic nature of these populations. Microsatellite data analyses suggest the network of spawning Chinook salmon was buffered from genetic impacts of severe population declines, an effect possibly mediated by the species’ substantial life history variation. These and other data will critically inform the development of effective salmon recovery strategies.