Culvert Replacement Enhances Connectivity of Stream Fish Communities in a Michigan Drainage Network

Culverts installed at road-stream intersections are pervasive in many watersheds and can function as dispersal barriers for aquatic organisms and fragment watershed connectivity.  We hypothesized that culvert removal would improve fish passage and restore ecosystem connectivity.  The objectives of our study were to: (1) characterize fish species relative abundances in three Michigan streams before and after culvert removal and (2) determine what effect our sampling methods may have on quantification of fish assemblage similarity.  We surveyed the upstream and downstream fish assemblages of the three study streams prior to, one year after, and three years after culvert removal.  In our study streams, relative fish abundance decreased but biomass of fishes remained constant, suggesting a shift in size structure toward larger individuals.  Similarity of upstream and downstream fish assemblages increased following culvert removal.  In addition, via a bootstrap analysis of 1,000 randomly selected Monte Carlo simulations per sample reach, we determined that large sample sizes of fishes were necessary to accurately and precisely measure community similarity.  However, increases in community similarity following culvert removal could be detected with sample sizes as small as 50 individuals.  Our study illustrates the value of culvert removal for enhancing fish passage and restoring stream connectivity.