River Ecology and Restoration - River Dynamics and Integrated River Management - page 675

( Micropterus salmoides ). Sunfish are medium sized, mid-water species, which tend to occur in pools or
other shallow-moving water. Most, but not all, are tolerant of environmental degradation. All feed on a
variety of invertebrates, although some larger adults may eat fish. Sunfish are included in the index
because they are particularly responsive to the degradation of pool habitats and to other aspects of habitat
such as instream cover.
Number of sucker species— The total number of sucker species (family Catostomidae ) collected,
excluding hybrids. Suckers are large benthic species that generally live in pools or runs, although a few
species are common in riffles. Some species are intolerant of environmental degradation, whereas others
are tolerant. Most species feed on insects, although a few also eat large quantities of detritus or plankton.
Suckers are included in the index because many of these species are intolerant to degradation of habitat
or chemical quality. Also, the longevity of suckers provides a multiyear integrative perspective.
Number of intolerant species— The total number of species, excluding hybrids, which are intolerant
of environmental degradation, particularly poor water quality, siltation and increased turbidity, and
reduced heterogeneity (e.g., channelization). Intolerant species are among the first to be decimated after
perturbation to habitat or water quality, and the species identified in metrics 2-4 may be included in this
group.
Proportion of individuals as green sunfish— In the Midwestern U.S., the green sunfish ( Lepomis
cyanellus ) increases in relative abundance in degraded streams and may increase from an incidental to
the dominant species. Thus, this metric evaluates the degree to which typically tolerant species dominate
the community. In many other IBIs, tolerant species in the sample are listed and the proportion of tolerant
individuals in the sample is computed and used as the metric in place of green sunfish.
Proportion of individuals as omnivores— The number of individuals that belong to species with an
adult diet consisting of at least 25% (by volume) plant material or detritus and at least 25% live animal
matter, expressed as a percentage of the total number of fish captured. By definition, omnivores can
subsist on a broad range of food items, and they are relatively insensitive to the change in the food base
of a stream caused by environmental degradation. Hybrids are included in this metric if both of the
parental species are considered omnivores. The dominance of omnivores occurs as specific components
of the food base become less reliable, and the opportunistic foraging habits of omnivores make them more
successful than specialized foragers.
Proportion of individuals as insectivorous cyprinids— Cyprinids that belong to species with an adult
diet normally dominated by aquatic or terrestrial insects, expressed as a percentage of the total number of
fish captured. Although insectivorous cyprinids are a dominant trophic group in streams in the midwestern
U.S., their relative abundance decreases with degradation, probably in response to variability in the
insect supply, which in turn reflects alterations of water quality, energy sources, or instream habitat. In
other regions the proportion of total insectivores to total individuals may provide better information for
this metric with a resetting of the scoring criteria.
Proportion of individuals as piscivores (top carnivores)— The number of individuals that belong to
species with an adult diet dominated by vertebrates (especially fish) or decapod crusteacea (e.g., crayfish,
shrimp), expressed as a percentage of the total number of fish captured. Some species feed on invertebrates
and fish as fry and juveniles. Hybrids are included in this metric only if both of the parental species
are carnivores. Viable and healthy populations of top carnivores indicate a healthy, trophically diverse
community.
Number of individuals in a sample— This metric evaluates populations and is expressed as catch per
unit of sampling effort. Effort may be expressed per unit area sampled, per length of reach sampled, or
per unit of time spent. In streams of a given size and with the same sampling method and efficiency of
effort, poorer sites are generally expected to yield fewer individuals than sites of higher quality.