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).