The Impact of Dredging on Heterogeneity and Fish Communities in Agricultural Streams of the greater Sandusky River Watershed, Ohio

Abstract

Headwater streams comprise about half of the total stream length in the U.S. They help control floods, transport suspended and dissolved matter, and connect upstream landscapes with downstream water bodies. They may also serve as spawning, feeding and nursery habitat for native fish species. Over the last century, however, many of these streams have been dredged into agricultural drainage ditches with homogenous habitat, straight channels and steep bank slopes. Due to the success of erosion control practices, dredging frequency has now been reduced in places and some ditches are returning to a more natural and heterogeneous morphology with meanders, pools, and vegetated benches. As a part of a 4-year project, 20 ditch segments (each 50m long) were block-seined in the Sandusky River drainage for their fish communities in June and September 2011 and sampled for selected habitat variables. Streams varied in time of last dredging and frequency resulting in their level of channel heterogeneity. A total of 6,887 fish belonging to 32 different species were netted, identified to species, assessed for condition, aged (adult, Young-of-Year), and released. Richness varied from 0 to 15 species and abundance varied between 0 and 1851 per 50m ditch segment. Fish species richness was positively correlated with stream heterogeneity in the horizontal and vertical plane of the wetted channel. Horizontal heterogeneity was a better predictor for the presence of more fish species. Species richness of YOY fishes was positively correlated with horizontal stream heterogeneity, while no relationship was detected between YOY species richness and vertical heterogeneity or percent plant cover. In spite of their sometime degraded conditions, ditches may replace important lost fish habitat, particularly when dredging practices are minimized. Opportunities to incorporate environmental considerations into the management of these channels, while maintaining the drainage function, should be considered.