BOX 1 Reservoir Fish Assemblage Index—Metric Characteristics

Reservoir Fish Species Richness and Composition Metrics

  • Total number of species—Greater numbers of species represent healthier aquatic ecosystems. As conditions degrade, species numbers decline.
  • Number of piscivore species—Higher diversity of piscivores indicates a better quality environment.
  • Number of sunfish species—Lepomid sunfish (excluding black bass, crappies, and rock bass) are basically insectivores; high diversity of this group indicates low levels of siltation and high sediment quality in littoral areas.
  • Number of sucker species—Suckers also are insectivores, but they inhabit the pelagic and more riverine sections of reservoirs. This metric closely parallels the metric for lithophilic spawning species (below) and may be deleted from future RFAI calculations.
  • Number of intolerant species—This group is made up of species that are particularly intolerant of habitat degradation. Higher numbers of intolerant species indicate better environmental quality.
  • Percentage tolerant individuals (excluding young-of-year)—A high pro- portion of individuals tolerant of degraded conditions indicates poor environmental quality.
  • Dominance by one species—Ecological quality is reduced if one species dominates the resident fish community.

is not yet enough information for inflow sampling locations on tributary reservoirs to establish criteria for fish community metrics at those sites.

The average of the sum of the electrofishing scores and the sum of the gill netting scores results in a RFAI for each station. The possible range of RFAI values is 12 (all metrics scored 1) to 60 (all metrics scored 5). This possible range is divided into five equal groupings to evaluate the overall health of the fish assemblage at each station (Table 7).

Discussions of the development of the RFAI and results of the fish evaluations for the 1991-1993 Vital Signs monitoring data are available in TVA technical reports (Brown et al, 1993; Hickman et al, 1994; Scott et al., 1992).

Overall Reservoir Health Determination

The methodology for evaluating overall ecological health combines the five indicators (DO, chlorophyll-a, sediment quality, benthic macroinvertebrates, and



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