Warmwater species fish passage in eastern Montana culverts

Transportation system planners, designers and managers recognize that fish passage through culverts is a concern. However, there is much contention concerning the impact that a given culvert can have on a fishery. This is particularly true for warm water prairie fisheries. In this project, a combination of three assessment techniques were used to examine fish passage at five culvert crossings in eastern Montana. The techniques used were longitudinal distribution surveys,direct observation of fish passage in field experiments, and modeling using the Fish Xing program.Results show a diverse fishery with as many as 21 species in a given reach. Distributional surveys showed no difference in fish species richness and almost no difference in fish abundance between the upstream and downstream sides of culverts. Direct observation of the four most abundant species found that when all species were combined, fish passed through culverts at an equal or greater rate than through reference reaches and only one individual species, longnose dace, did not. The Fish Xing model tended to be conservative, even when calibrated to local hydraulics at each culvert. The strongest estimator of fish passage was to overlay the Fish Xing results and the field observations onto a hydrograph of the stream system to predict passage windows, or time periods where passage is predicted to not be restricted