Evaluating the Potential of Passive Stream Restoration as a Method to Minimize the Impact of Whirling Disease on Native Fish

Habitat alteration, exotic species, and disease are three factors that often affect native species composition, abundance and persistence. Individually, each of these factors may have predictable effects or even be inconsequential; however when combined there may be unpredictable and synergistic effects at the population level. We have identified an important population of native Bonneville cutthroat trout (Oncorhynchus clarkii utah) in Northern Utah that are potentially impacted by livestock grazing and Myxobolus cerebralis the parasite that causes whirling disease. The relationship between the whirling disease life cycle (e.g., tubifex worms), and habitat degradation caused by livestock grazing (e.g., sedimentation) represents an interaction between two factors with strong potential for synergistic effects. We are investigating means to mitigate this interaction by implementing a passive stream restoration project. Spawn Creek, a secondary tributary to the Logan River, was identified as the restoration site, due to its importance as a location for the spawning and rearing of Bonneville cutthroat trout, occurrence of livestock grazing, and positive tests for the presence in M. cerebralis. Passive restoration was implemented by removing the source of habitat alteration through the exclusion of livestock grazing. We evaluated the effectiveness of this method in 1) restoring stream and riparian habitat, 2) improving fish health and viability, and 3) minimizing the impact of whirling disease. Our study approach is an asymmetrical Before After Control Impact design. Here we report on data collected during two Before years, and the first After year including both aspects of fish health and viability and abiotic and biotic stream factors as response variables potentially related to M. cerebralis and likely to respond to stream restoration. Currently there are no management methods to eliminate whirling disease from natural systems, though this approach may provide the means by which impacts on native fish may be minimized