The Influence of Density-Dependence and Artificial Propagation on Natural Productivity of Spring Chinook Salmon in the Wenatchee Watershed

Density-dependence and artificial propagation have repeatedly been shown to influence natural productivity of salmon; however, the relative influence of these factors has rarely been compared to determine how they reduce productivity across a range of spawner abundances.  Comparisons can be challenging because of a correlation between hatchery-origin spawner abundance and total spawner abundance.  Density-independent survival of stream-type Chinook salmon in the Wenatchee River Basin was modelled and compared to density-dependent and hatchery-origin influenced fish survival across a range of spawner abundances.  Other methods were also explored to estimate mortality influenced by density and artificial propagation and to tease out confounding factors.  Evidence for both density-dependent and hatchery-origin caused mortality was detected.  The proportion of total mortality attributed to density-independence, density-dependence, and artificial propagation was estimated and compared to spawner abundance.  Differences in the proportion of mortality caused by various factors at increasing spawner abundance can help explain conflicting results from published studies.  Furthermore, results can have important implications for whether habitat actions, artificial propagation, or both should be employed to achieve management objectives.