Retrospective weight-of-evidence analysis identifies substrate change as the apparent cause of recruitment failure in the upper Columbia River white sturgeon (Acipenser transmontanus)

A weight-of-evidence evaluation of the potential cause of white sturgeon (Acipenser transmontanus) recruitment failure in the upper Columbia River evaluated 12 recruitment-failure hypotheses based on nine criteria. Recruitment-failure timing was estimated by identifying breakpoints in the hindcasted recruitment time series for three of four spatially distinct groups. Observed spatial and temporal recruitment decline patterns were then compared with expected patterns for each hypothesis (e.g., flow, temperature, turbidity, contaminants, and changes to the riverine fish community). The weight-of-evidence evaluation also considered criteria including coherence with theoretical, factual, and biological evidence and responses to impact reversal. Recruitment failure began about 1968, coincident with the initiation of upstream mainstem flow regulation. An 8- or 9-year lag in the recruitment decline of the Waneta group was particularly informative for hypothesis evaluations. The identification of increased fine substrates at spawning sites as the most plausible explanation for chronic recruitment failure has important implications regarding the apparent life stages affected and potential restoration approaches.