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Figure 11-15 Long-term trends in Ohio River fish abundance at Cincinnati and Louisville. Source: W. D. Pearson, Water quality in North American river systems, eds. C. D. Becker and D. A. Neitzel, © 1992, Reprinted with permission: Battelle Press, Columbus, OH.

cies captured was found as well, indicating improved habitat quality. The Ohio EPA has also conducted fish studies along the river. Their studies have found an Index of Biotic Integrity (IBI) near North Bend between 46 and 48 (Ohio EPA, 1992). This is a fair to good rating, indicating habitats where tolerant and intolerant benthic species are both found. The IBI, developed by Karr (1981) for use in midwestern streams, has been adapted for use in other areas. This index is a composite of 12 ecological attributes of fish communities, including species richness, indicator taxa (both intolerant and tolerant), trophic guilds, fish abundance, and incidence of hybridization, disease, and abnormalities (Karr et al., 1986). IBI scores range from a low of 12 to a high of 60. A score of 12 is assigned to conditions where no fish are present even after repeated sampling; a score of 60 is assigned to conditions comparable to the best habitats without human disturbance (Karr et al., 1986). Benthos are particularly good indicators of long-term trends in water quality because the species are generally sedentary and have long life spans. For pollution studies, benthos are divided into three categories, and intolerant species are indicative of good water quality because of their inability to survive in, or intolerance of, low DO concentrations. Ohio EPA's sampling at North Bend in 1991 found a total of 23 species, with one intolerant species among them (Sanders, 1992a, 1992b; Plafkin et al., 1989).

Water quality improvements in the Ohio River have benefited both commercial and sport fisheries (Figure 11-15). Sportfishing, important recreationally and for tourism, began returning to the river in the mid-1980s. In 1982, the Bass Anglers Sportsman's Society held the Bass Champs Invitational at Cincinnati because of the reported bass catch in the river (ORSANCO, 1981). Such contests are now commonly held along the river.

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