TABLE 6 Reservoir Area Metric Scores and Corresponding Ratings

Sum of Reservoir Benthic Community Metric Scores

Benthic Rating


1 (poor)




3 (fair)




5 (good)

lated similarly, using the proportion calculated for the dominant taxon in each sample, even if the dominant taxon differs among samples at a station. This allows more discretion to identify imbalances at a station than would developing an average for a single dominant taxon for all samples at the station.

The basis for evaluation criteria is the range of values found in the available database (all Vital Signs benthic monitoring data from 1991 to the present) for each metric. For each metric at each reservoir area (forebay, transition zone, and inflow) and reservoir type (run-of-the-river and tributary), the database values are divided into three groups using Ward's minimum variance analysis (SAS Institute, 1989). This procedure places observations into three homogeneous groups of approximately equal size. The groups are sorted and categorized as poor, fair, or good. Scoring criteria represent values between the highest and the lowest value in each group. The current year's results for each metric are compared with these criteria and assigned scores of 1 (poor), 3 (fair), or 5 (good) depending on which group they fall in. Scores are summed by reservoir area to yield an overall benthic rating for each location (Table 6).

Fish Assemblage

A Reservoir Fish Assemblage Index (RFAI) (Hickman et al., 1994) is used to rate fish assemblages as they relate to the overall ecological health of the reservoir. The RFAI is based on 12 metrics in 4 areas (Box 1) with scoring criteria specific to either run-of-the-river or tributary reservoirs. Scoring criteria also are specific for the type of sampling location within reservoirs—forebay, transition zone, or inflow; and for the type of sampling gear (i.e., electrofishing for littoral fish communities and gill netting for pelagic fish communities).

Each metric is assigned a score of 5, 3, or 1—representing good, fair, or poor conditions, respectively. Because of the distinct habitat differences among reservoirs and sampling locations (and the differences in the fish assemblages that they support), different scoring criteria are used according to reservoir type (run-of-the-river or tributary storage reservoirs), sampling location (forebay, transition, or inflow), and type of sampling gear (electrofishing or gill netting). There

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