QUANTIFYING THE FISH COMMUNITY RESPONSE TO DAM REMOVAL: THE CASE OF THE OTTAWA RIVER, NORTHWEST OHIO

Barriers in rivers may impact the migration and distribution of fish and, consequently, the biological community as a whole. Such impacts are often cited in support of dam removal but few studies have actually quantified fish community structure and composition pre- and post-removal. The planned removal of a low-head dam in the Ottawa River (Ohio) provided us with an opportunity to field test a standard protocol for such an evaluation.

We applied routine ecological metrics to contrast the structure and composition of the fish community in the Ottawa River upstream and downstream from this dam, the most-downstream barrier in the watershed. Using block nets and seines, the fish community was sampled thoroughly and repeatedly in both locations during the spring and summer of 2003 and 2004. Up to 277 fish per sampling event were identified to species, measured, assessed for parasites and breeding condition, and released unharmed. We measured relevant habitat conditions in both sampling locations to quantify differences independent from the dam that may impact the fish community. Upstream and downstream Qualitative Habitat Evaluation Index (QHEI) scores were comparable, as were measurements of dissolved oxygen, specific conductivity, pH, temperature, canopy cover and discharge at each sampling event. Species richness, rarefied for sample size, varied between sites and sampling dates and was higher downstream. The Index of Biotic Integrity (IBI) was stable at 40 (fair) downstream and ranged from 28 (terrible) to 33 (poor) upstream. Shannon diversity scores at the upstream site were 0.77 to 1.09, lower than the downstream range of 1.91 to 1.93. Species present downstream but absent upstream included several sunfish (Lepomis spp.), Northern Pike (Esox lucius) and Yellow perch (Perca flavescens).

Despite its small size, the dam has a considerable impact on the fish community composition and structure in the Ottawa River. To complete the field test, our study will be repeated following the removal of this dam scheduled for the summer of 2006.