Number of Trout and Sunfish Species
This metric was adopted as a hybrid for warmwater and coldwater streams. The metric is
similar to that used in a combined coldwater-warmwater version of an IBI developed in
Ontario (Steedman 1988), but designed for high-gradient rather than low-gradient streams.
Both sunfish and trout are water-column species sensitive to habitat degradation and loss of
instream cover (Gammon et al. 1981; Angermeier 1983). In coldwater streams where sunfish
are typically absent, trout fill a similar ecological niche and may be used to replace sunfish.
Trout are equally, if not more sensitive to habitat degradation. The relationship between trout
populations and habitat is well documented (Peters 1967; Hunt1969; Meehan 1991). Metric
recalibration has resulted in the elimination of green sunfish and bluegill, as these species are
designated as tolerant by the USEPA (Plafkin et al 1989).