River Ecology and Restoration - River Dynamics and Integrated River Management - page 674

10.3.2.4 Indices of Biotic Integrity

1) Karr's IBI
Fish represent the top of the aquatic food chain, and, thus, the quality and composition of the fish community
comprises the best measure of the overall health of the aquatic community. This is because the fish
community integrates the effects of the entire suite of physical, chemical, and biological stresses on the
ecosystem. A fish community index should include at least one metric for each of the five attributes of fish
assemblages (Simon and Lyons, 1995): species richness and condition, indicator species, trophic function,
reproduction function, and individual abundance and condition.
Considering the foregoing considerations, Karr (1981) proposed and revised (Karr et al., 1986) the
Index of Biotic Integrity (IBI) to evaluate stream quality at the fish community level. The Karr's IBI is
comprised of 12 metrics to define fish community structure. The index accounts for changes in fish
community richness and allows for comparison of fish community composition with values for similar-sized
streams. The applicability of the IBI concept has been demonstrated in a wide variety of streams types
(Miller et al., 1988). As recommended by Karr et al. (1986), IBI metrics require adjustment for the region to
which the index is applied. The basic components of Karr's index are listed in Table 10.3. It is recognized
that stream size is an important factor when refining the IBI to a geographical region.

T able 10.3 Karr's Index of Biological Integrity (IBI) (after Karr et al., 1986)

Scoring criteria

Category Metrics

5 3 1

1. Total number of fish species
2. Number and identity of darter species
3. Number and identity of sunfish species
4. Number and identity of sucker species
5. Number and identity of intolerant species

Expectations for metrics 1-5
vary with stream size and region

Species richness
and composition

6. Proportion of individuals as green sunfish <5% 5%-20% >20%

7. Proportion of individuals as omnivores <20% 20%-45% >45%

Trophic
composition

8. Proportion of individuals as insectivorous Cyprinids >45% 45%-20% <20%

9. Proportion of individuals as piscivores (top carnivores) >5% 5%-1% <1%

Expectations vary with stream
size and region

10. Number of individuals in sample

Fish abundance
and Condition

11. Proportion of individuals as hybrids 0% 0%-1% >1%

12. Proportion of individuals with disease, tumors, fin
damage, skeletal anlmalies (DELT)

0%-2% 2%-5% >5%

The definitions of the twelve metrics are described as follows (Karr et al., 1986, Lyons, 1992):
Total number of species— The total number of species collected at a site, excluding hybrids and
subspecies. The number of fish species supported by streams of a given size in a given region decreases
with environmental degradation, if other features are similar.
Number of darter species— The total number of darter species (family Percidae ) collected, excluding
hybrids. Darters are small benthic species that tend to be intolerant of many types of environmental
degradation. They are mainly insectivorous, and for many of them riffles or runs are preferred habitats.
These species are sensitive to degradation, particularly as a result of their need to reproduce and feed in
benthic habitats. Such habitats are degraded by channelization, siltation, and reduction in oxygen content.
Number of sunfish species— The total of sunfish species (family Centrarchidae ), including rock bass
( Amobloplites rupertris ) and crappies ( Pomoxis species), but excluding hybrids and black basses