Abstract

The overall goal of the Midwestern regional-scale assessment was to identify river reaches in the Glacial Lakes Partnership regions (focusing on Michigan, Minnesota, and Wisconsin) that are most vulnerable to potential impacts of projected climate and land use changes. Because fish assemblages are strongly influenced by river water temperature and flow regimes, which are in turn affected by climate and land-use conditions, we will attempt to model fish habitat response to climate and land use changes through changes in temperature and flow.

This project intended to: (1) develop three models that predict daily summer temperature for all river reaches in each state; (2) develop a single model to predict non-winter flow regimes for all river reaches in the region; (3) develop relational models among fish, water temperature regime, and flow regime; and (4) develop fish habitat scores that allow us to compare the fish assemblages, water temperature, and flow regimes under current and future climate and land-use conditions. 

Products from this study:

• Identifying indicators and quantifying large-scale effects of dams on fishes (not open-access): Although localized effects of individual dams on stream fish assemblages have been relatively well-studied, less is known about the effects of multiple dams within a stream network on fishes and the patterns that emerge when the combined effects of individual and multiple dams are viewed across entire river basins, ecoregions, and states. This study evaluated multiple stream network fragmentation metrics representing localized (e.g., distance-to-dams) and cumulative (e.g., total upstream reservoir storage) dam influences on streams in Michigan, Wisconsin, and Minnesota, developing an approach for identifying suitable fish indicators of dam effects. We used change point and correlation analyses to determine associations of stream fish catch per unit effort and various stream network fragmentation metrics with data from more than 2000 fish survey sites stratified by stream size, thermal regime, and ecoregion. Of the identified indicator species, predominantly warm water, large river, and/or lentic species were positively associated with stream network fragmentation, whereas cold and coolwater lotic species were negatively associated with fragmentation. These results suggest a combination of downstream thermal effects and upstream influences from impoundments generated by dams. Variance partitioning analyses based on identified indicator species revealed greater upstream-dominated dam influences in headwaters than mid-sized streams, and a greater relative influence of dams vs. other non-dam anthropogenic influences in cold streams than warm streams. Overall, a combination of localized and cumulative fragmentation metrics, as well as upstream and downstream-oriented measures, were influential in indicator species responses, emphasizing the importance of selecting a diversity of fragmentation metrics when assessing effects of dams on stream fishes. Understanding multiple dam influences on stream fishes, including localized effects from individual dams and cumulative effects from all dams within a river basin, would provide useful information for a variety of management activities, including dam operation and dam removal prioritization. Dams significantly affect conservation and management options for stream fishes, with identification of multi-scale dam influences on fishes being critical to restoration and maintenance of aquatic biodiversity throughout the world.