Identifying strategic opportunities for road crossing improvement to benefit stream fishes

Road crossings over streams can act as barriers to fish movement. Because road crossings are ubiquitous in developed areas, their cumulative effects have the potential to limit fish population persistence at large scales. The objective of this study was to create a method for identifying road crossings whose reconstruction would most benefit stream fishes by restoring stream network connectivity. We demonstrate the method through a case study in the Pine-Popple watershed in Wisconsin. We first conducted a comprehensive field survey to identify crossings that are likely to impede fish movement. We then used a GIS to evaluate the influence of each crossing on the connected neighborhood size of all streams in the watershed, which is an index of the potential benefit of eliminating each barrier. The benefit index was then divided by a reconstruction cost estimate to create a benefit/cost ratio for prioritizing projects. Sixty-seven percent of the 169 surveyed road crossings were determined to be a barrier to movement of at least some species or life stages of fish. The distribution of benefit/cost ratios was strongly skewed, which supports prioritizing projects in this watershed. The method is being applied to several other watersheds in the Great Lakes basin.