Comparative Biophysical Complexity of Pacific Rim Salmon Rivers

A team of American and Russian scientists used a unified sampling protocol at 6 sentinel and 18 synoptic rivers in western USA, British Columbia, Alaska and Kamchatka to examine salmon productivity in relation to physical habitat, food webs, life histories, juvenile densities and spawner returns.  Measures from this Salmonid Rivers Observatory Network (SaRON) were used to calibrate satellite data that regionalized interpretations concerning influences of harvest and climate change on measured and potential salmon productivity of the North Pacific Rim.  Scalable metrics describing geomorphic complexity of 1500 rivers were extracted from a novel satellite remote sensing data base.  This biophysical data base also was populated by daily flows and temperatures predicted by a water and heat flux model driven by 5 downscaled IPCC forecasts out to year 2100.  The model was 80% accurate in reproducing historical records.  Using clustering and PCA analyses, we showed that a) that rivers with high physical complexity have the highest salmon based biodiversity and productivity, unless overharvested, and b) that major changes in biocomplexity will result from ongoing climate warming, and c) floodplain rivers, especially in Kamchatka, will be most resilient to climate change.  Densities of salmon juveniles and returning adults per unit of habitat was an order of magnitude higher in Kamchatka rivers for all species in relation to many NA rivers with equally complex and abundant physical habitat. We concluded that productivity of Pacific Rim salmon is coherent with habitat complexity, unless trumped by over-harvest and density dependent and other interactions associated with introductions of hatchery fish.  Even for NA rivers south of the Skeena, where the human footprint is high, habitat per se generally is not limiting salmon productivity in freshwater, owing apparently to the interactive legacy of harvest and hatchery intervention.