Number of Individuals in the Sample

(excluding tolerant species)

This metric measures the abundance of fish captured from a specified area or stream

reach and is used to distinguish streams with severe water quality impairment. Like the

original IBI (Karr 1981), catch per unit effort is used to score this metric. Severe toxicity

and oxygen depletions are examples of perturbations often responsible for extremely low fish

abundance. Tolerant species have been excluded from this metric, as often these species

thrive and are numerous under degraded conditions (Ohio EPA 1988).