Road Crossings Limit Northern Pike Access to Seasonal Spawning Habitat

Recruitment of juvenile northern pike in Green Bay of Lake Michigan has been reduced by loss of tributary spawning habitat, through both habitat degradation and barriers to access. Upgrading or improving road crossings (typically culverts) to facilitate fish passage has the potential to be an efficient way to increase pike recruitment because management action at a very small scale - the width of a road - can lead to accessibility of large expanses of breeding habitat. However, because there are thousands of crossings whose improvement could potentially benefit pike, rigorous methods for prioritizing restoration efforts are needed. We are using a GIS-based analytical approach to evaluate barriers on the proximity, amount, and quality of habitat that would be reconnected by their removal. Prioritization is based on this measure of benefit divided by the estimated cost of replacing a barrier with a fully passable structure, and could also account for potential inland spread of invasive round goby and sea lamprey. Because successive barrier removals have non-linear effects on connectivity, an iterative modeling approach is used to adjust priority rankings based on the sequence of barrier removal. These methods provide a quantitative basis for optimizing efforts to restore tributary network connectivity and spawning habitat for migratory fishes.