Selectivity of Impingement at Power Plants along the Ohio River

Impingement abundance monitoring and standardized fish sampling in 2005 and 2006 near 15 Ohio River power plants as part of the Ohio River Ecological Research Program suggested impingement of fishes at intake structures was selective and did not necessarily provide a representative characterization of assemblages in the source water. We compared species composition and relative abundance from the two data sets to evaluate potential explanations for the presence, absence, or disproportionate occurrence of fishes in the impingement samples relative to their abundance in the river as measured by seasonal electrofishing and seining collections. The impingement study demonstrated similarities in species composition among power plants over nearly 1,400 river kilometers of the Ohio River, whereas the river surveys showed that the abundance of some species varied considerably over the course of the river. As expected, clupeids dominated the impingement collections, but at much higher levels than suggested by the river surveys, while other forage species, especially emerald shiner and channel shiner, were under represented in the impingement collections. During the two-year study, 32 species collected during the river surveys were not impinged whereas 13 species were impinged that were not collected during the river surveys. The impingement study showed that many species in the Ohio River are not particularly susceptible to impingement because their behavior, habitat preferences, or low population levels reduce the likelihood of them being impinged. This was especially evident for cyprinid, darters, and redhorse. The opposite was true of the abundant, pelagic schooling clupeids that were occasionally impinged at very high rates, often during periods with declining water temperatures. Freshwater drum and channel catfish were also impinged at much higher rates than would be predicted based on their abundance in the river collections.