THE INFLUENCE OF CHANNEL GEOMORPHOLOGY AND DISTURBANCE PROCESSES ON THE SPATIAL STRUCTURE OF CHINOOK SALMON POPULATIONS IN RIVERS

We examined the relationships among Chinook salmon population spatial patterns and habitat configuration at the channel network scale using spawner distribution and channel attribute data.  Our findings show redd density is consistently organized around specific river features that are large, persistent, and non-uniformly distributed within channel networks, including tributary junctions, landslides, and canyons.  We also found periodic high use of habitats that are either of low quality or periodically inaccessible, or both, but were adjacent to larger high-quality habitats.  Based on these findings, we propose there are unique areas (i.e., core areas) within the river network that consistently provide habitat for a large proportion of the population.  These areas are generally large (i.e, support congregations of spawners), physically persistent (i.e., habitat suitability exists over timeframe of multiple generations), and consistently accessible to all spawners.  The spatial distribution of these core habitats is related to the geometry of branching channel networks, the relative size of confluent basins, valley heterogeneity, and the potential for channel disturbances.  These findings combined with our understanding of salmon ecology suggest that population spatial structure is formed by the interaction between habitat spatial/temporal characteristics (i.e., distribution, size, persistence, accessibility) and population dispersal mechanisms (i.e., homing, competition, and habitat selection).  This information is helpful for the identification and prioritization of habitat protection and restoration actions that are necessary for the recovery and sustainability of endangered salmon populations.