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

Abstract

AbstractCulverts installed at road–stream intersections are pervasive in many watersheds and can function as dispersal barriers for aquatic organisms, thereby fragmenting watersheds. We hypothesized that the replacement of culverts with bridges would restore ecosystem connectivity via remediation of dispersal barriers. Our study objectives were to (1) characterize fish assemblages in three Michigan streams before and after culvert replacement by bridges, and (2) determine the effect of fish sample size on our ability to quantify fish assemblage similarity. To address the first objective, we surveyed the fish assemblages of the three study streams (upstream and downstream of the culvert) prior to, 1 year after, and 3 years after culvert removal via standardized electrofishing. The similarity of upstream and downstream fish assemblages increased by 9–25% following culvert removal. Relative fish abundance decreased but biomass of fishes remained constant, indicating a shift in size structure toward larger individuals. To address the second objective, we conducted a bootstrap analysis for all samples. Large sample sizes of fishes (150–350 individuals) were necessary to accurately and precisely measure community similarity. However, changes in community similarity could be detected with relatively small samples (50–100 individuals). Our study illustrates the ecological potential of culvert removal for restoring stream connectivity.