Evaluating Fish As Vectors of Contaminants: Implications for Dam Removal

Dam removal or modification is becoming a common technique for reconnecting aquatic riverine ecosystems and can alleviate issues associated with aging structures.  Despite the numerous ecological benefits of dam removal, there can also be negative consequences.  We evaluated fish as potential vectors of contaminant transfer on the Cass River (Frankenmuth, Michigan) before a dam is modified, to assess the potential risk of harm to aquatic and terrestrial ecosystems.  Golden redhorse and smallmouth bass were captured upstream and downstream of the dam and round goby, walleye, and white sucker were captured downstream.  Tissues were analyzed for total (∑) polychlorinated biphenyls (PCBs), ∑ brominated diethyl ethers (BDEs) and methyl mercury (MeHg).  Hazard quotients (HQs) were quantified by fish species and based on injury to bald eagle embryos.   Downstream of the dam golden redhorse had greater concentrations of ∑PCBs (t-test, df = 22, P < 0.001) and ∑BDEs (t-test, df = 22, P = 0.017), while smallmouth bass had greater concentrations of ∑PCBs (t-test, df = 14, P = 0.003) and MeHg (t-test, df =14, P = 0.020).  Based on hazard assessment, ∑PCBs in smallmouth bass, walleye, white sucker, and golden redhorse downstream of the dam may present a risk to bald eagles.