Weber River Metapopulation and Source-Sink Dynamics of Native and Endemic Fishes

In the Intermountain West, cutthroat trout subspecies have declined dramatically partially owing to habitat fragmentation.  As a result, few populations of Bonneville cutthroat trout (BCT; Oncorhynchus clarkii utah) remain that demonstrate fluvial life-histories.  Fluvial BCT are thought to persist in the Weber River, Utah, although this system is highly fragmented.  In 2011, we initiated a study to examine contemporary and historic connectivity between BCT subpopulations in tributary and main-stem reaches, and to identify factors limiting these populations.  We used population size structure and mark-recapture data to document source-sink dynamics among contemporary subpopulations.  Population size structure differed substantially between tributary and main-stem subpopulations, with small, resident BCT in tributaries and large, potentially fluvial BCT in the main-stem.  Movement between habitats was limited; however, several large fish attempted to spawn in tributaries during a 10-year flood in 2011.  We used mark-recapture analysis to document that many large BCT remained below barriers in tributaries during the spawn and returned to the main-stem after peak runoff.  We suggest that limited connectivity occurs in certain years and the fluvial life history expression prevails.  Collectively, this research will provide managers with information vital to designing the best conservation strategy for BCT in the Weber River.