IBI’s: How It’s Done

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(1) Regional Fish Fauna The physico-chemical environment

determines community structure and composition

A fish’s habitat requirements and tolerances speaks toward the local environmental conditions

Distribution and life history very prominent in literature

(1) Evaluation of Metric Suitability

Scoring range Broad range desirable

Variability Signal / Noise test

Responsiveness Sensitivity to physical and chemical variables

Redundancy Attempt to reduce among metrics(Hughes et al. 1998)

(1) Reference Condition Least impacted sites within the area

of study May be stratified by watershed,

ecoregion, etc. Typically use a quantile approach

where the highest or lowest* 5-10% set the baseline conditions

*Highest or lowest depends whether the metric is positive or negative scoring

(2) Sampling Approaches / Design

Probabilistic

Targeted

Hybrid Approaches

Site Selection

Representative reach with at least 1 riffle-pool sequence

Reach length based on mean stream width with a maximum and minimum length

Sampling the Fish Community Backpack electrofishing with a seine net

Identification and Tabulation

Fish are generally not weighed and measured but identified to species

Fish often examined for DELT anomalies (deformities, eroded fins, lesions, and tumors)

IBI Metrics

Individuals provide little information but proportions of the community are very telling

Scaling allows for comparisons across a variety of sizes of waterbodies

Calculation of IBI score

Raw metrics are divided by scores from reference sites

Scored metrics are summed and total is corrected for a 100 point scale

Assignment and Interpretation

Total score is assigned to some predetermined integrity class Example: 80-100 = Good 60-80 = Fair < 60 = Poor

Interpretation is based on assignment and goals and objectives of assessment