Au Sable Resilience Project Final Report

Michigan’s rivers and the species they support provide numerous ecological, economic, and social benefits to residents of the Great Lakes region. Anticipated changes in precipitation and air temperature due to climate change only further jeopardize these valuable systems. Over the past four years, our team of researchers from Michigan State University and the University of Georgia hosted a series of four in-person workshops and more than 15 virtual meetings with numerous stakeholder groups (hereafter, the working group) interested in resilience planning for the Au Sable River, with a focus on the coldwater fishery. The purpose of this research was to (1) use a structured decision-making (SDM) process to develop a framework for aiding future decision making related to resilience in the Au Sable River—the Au Sable Resilience Decision Framework, and (2) develop decision support science to further understanding of the current and future status of the river, its trout populations, and response to anticipated future changes. The goal of this process was not to aid a specific decision, but to develop a holistic process to identify and address aspects of resilience and sustainability of Michigan rivers while considering changing climate and other stressors. The working group developed a problem statement to guide decision making for resilience in the Au Sable River, identifying key issues and the scope of the decision. The group identified two overarching, strategic objectives: (1) Maximize ecological resilience and (2) Improve and sustain the coldwater fishery. They further described three fundamental objectives (1) Maximize wild coldwater fishery production, (2) Minimize costs, and (3) Maximize longevity of management. We developed a non-exhaustive, cumulative list of potential management alternatives (i.e., potential actions that could be implemented) to achieve the fundamental objectives. Users of the Au Sable Resilience Decision Framework can build ‘packages’ or ‘portfolios’ of actions for comparison and evaluation of tradeoffs. Concurrent with the decision analysis process, our research team developed models for temperature conditions and trout populations to evaluate performance measures related to the coldwater fishery objective. The results of the current condition models show that many reaches across the Au Sable exceed safe angling temperatures (21.11 °C or 70 °F) for multiple days in July, with some reaches even exceeding lethal brook trout temperatures (25.3 °C or 77.54 °F). Future stream temperature projections revealed variable amounts of warming among reaches in response to changes in air temperature for three different climate chang scenarios. In the scenario with the most warming, some reaches are predicted to increase in mean July stream temperature as much as 2.99 °C. These results provide insights into management actions that could be taken to influence thermal magnitudes, rate of change, and frequency of thermally stressful events. The trout population model was developed to explore how brook and brown trout abundances may change through 2080 under varying climate change and management scenarios. Results revealed that both species are projected to decline most under conditions of high climate change, with brook trout exhibiting greater sensitivity than browns. Management actions such as maintaining or adding wood and woody debris can help buffer these declines, but they do not fully prevent them. Spatial variation across the watershed was evident—with the reaches near Frederic, MI, predicted to experience the greatest losses, while Middle Branch Big Creek near Lovells, MI shows the least decline. The results here provide both watershed-level and spatially explicit insights to guide management priorities, identify areas for focused intervention, and highlight areas where uncertainty is highest and additional data collection and research would be most valuable. This report and publications from this project can serve as a guide for applying an SDM process for resilience and sustainability of Michigan’s rivers and trout populations. We document the decision-support science developed during this project, as such models could be expanded and applied to other watersheds. Our multi-faceted approach provides critical information for managing the Au Sable, leading to growing consensus among the region’s stakeholders on challenges facing the river as well as courses of action, ultimately contributing to greater chances of successful conservation of this iconic fishery.