BOX 3 Index of Biotic Integrity Metrics

Stream Fish Species Richness and Composition

  • Number of native species
  • Number of darter species
  • Number of native sunfish species (excluding Micropterus sp.)
  • Number of sucker species
  • Number of intolerant species
  • Percentage individuals as tolerant species

Stream Fish Trophic Structure

  • Percentage omnivores
  • Percentage specialized insectivorous minnows and darters
  • Percentage piscivores

Stream Fish Abundance and Condition

  • Catch rate (average number per unit of sampling effort, seine hauls, and electrofishing)
  • Percentage individuals as hybrids
  • Percentage individuals with poor condition, injury, deformity, disease, or other anomaly
Stream Fish Community

A modified version of Karr's (1981) Index of Biotic Integrity is used to assess the condition of the resident fish community at monitoring locations. An index and rating are produced for each site by applying the 12 metrics in Box 3.

Actual values obtained for each of these metrics are scored poor, fair, or good (1, 3, or 5) against values that would be expected at reference sites. The 12 metric scores are summed to produce an index ranging from 12 to 60, and the fish community at the stream sampling location is rated as poor (index < 36), fair (index 40-44), or good (index > 46). Professional judgment is used to rate fish community index values between 36 and 40 and index values of 45. These determinations are based on factors such as which of the 12 metrics rates poorest, the condition of the coexisting macroinvertebrate community, and previous Index of Biotic Integrity ratings for the station.


The overall ecological health ratings for the 11 run-of-river reservoirs ranged from 58 to 88 percent in 1993 (Figure 5). Of the 11 reservoirs, 4 rated good (75-

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