Fish Habitat Improvement in Box Culverts: Management in the Dark?

Abstract

The effects of limestone baffles on the hydrological and fish assemblage characteristics of two separate 2.4-m-wide box culverts along the course of a cold headwater trout stream in southeastern Wisconsin were examined. Alternating limestone baffles were placed along the upstream half of one culvert, and the adjacent downstream half was left unmanipulated. The effects of the baffles on water depth, velocity, substrate, and fish abundance were assessed by comparing sites (control versus manipulated) among years from 1994 to 1996 (5, 18, and 32 months after manipulation). The manipulated section exhibited greater mean and variance in depth, velocity, and substrate composition, resulting in a more dynamic and natural stream channel compared with the control reach. Fish abundance and species diversity were greater within the manipulated section than in the control. In addition, average total fish species abundance and diversity within the section with the experimental baffle were comparable with adjacent sites in the natural stream directly upstream and downstream from the culvert. Baffles were placed along the entire length of a second culvert, which resulted in stream channel and fish assemblage characteristics similar to those observed in the manipulated section of the first culvert. These results demonstrate that manipulations within box culverts can increase habitat heterogeneity and enhance resident stream fish abundance and diversity. This alternate baffle design offers managers an inexpensive way to increase fish abundance and diversity and to help mitigate the loss of habitat caused by culverts in stream systems.