Assessing effects of sediment-reducing agriculture conservation practices on stream fishes

Abstract

Improving conservation of stream fish assemblages in agricultural landscapes requires both retrospective assessments of the effects of applied conservation practices (CPs) and forecasting the extent of CPs needed to achieve conservation goals. We assessed soil CPs applied by producers, in partnership with the USDA's Natural Resources Conservation Service (NRCS), based on their effectiveness at improving stream fish assemblages in the Missouri River basin. Multiple-regression models were used to predict the combined watershed scale effects of physiography, anthropogenic threats, and soil CPs on abundance of lithophilous spawning fishes, a reproductive guild sensitive to sedimentation. Two scenarios of lithophilous spawning guild abundance were predicted for each stream segment where (1) base condition of guild abundance assumed no CPs were applied and (2) a conservation condition abundance, which accounted for the effects of applied CPs. Abundance of the lithophilous spawning guild was positively associated with applied soil CP density. Models revealed that streams generally needed more than 50% of the agricultural land within their watershed to be treated by soil CPs to see significant improvement in the lithophilous spawning guild. Densities of currently applied CPs were predicted to mitigate impacts to this guild in less than 2% of assessed Missouri River basin stream segments. Restoring fish populations across the agricultural landscapes of the Missouri River basin will require managers to set realistic conservation goals and strategically implement CPs by prioritizing and allocating limited resources at multiple spatial scales (watershed and locally) because of the high density of CPs needed to see improvements in the fish community.