River Ecology and Restoration - River Dynamics and Integrated River Management - page 676

Proportion of individuals as hybrids— This metric is difficult to determine from historic data and is
sometimes omitted for lack of data. Its primary purpose is to assess the extent to which degradation has
altered reproductive isolation among species. Hybridization may be common among cyprinids after
channelization, although difficulties in recognizing hybrids may preclude using this criterion with darters
in addition to cyprinids. Sunfish also hybridize quite readily, and the frequency of their hybridization
appears to increase with stream modifications.
Proportion of individuals with disease, tumors, fin damage, and skeletal anomalies (DELT)— The
number of individual fish with skeletal or scale deformities, heavily frayed or eroded fins, open skin
lesions, or tumors that are apparent from external examination, expressed as a percentage of the total
number of fish captured. DELT fish are normally rare except at highly degraded sites.
Sampling of fish to determine these metrics is done on a reach basis. In Wisconsin, for example, a
stream reach is defined as a minimum of 35 times the mean stream width based on at least 10 field
measurements per site (Lyons, 1992). The results of the reach sampling are combined to define a
sampling site.

2) IBI Examples
Karr's IBI concept has been adapted and modified from its midwestern U.S. beginnings for application
throughout the world. Some IBIs simply adjust the scoring criteria as appropriate for their region of
application, whereas other IBIs have combined new metrics with Karr's metrics. More than 40 fish metrics
have been utilized in the various IBIs used in the U.S. (Limnotech, 2009).
The IBI developed for Taiwan (Hu et al., 2005) is an example, where the majority of Karr's original
metrics (with slight modifications) were applied, but the scoring criteria were modified (Table 10.4).
Other than the scoring criteria modifications, the main differences in the Taiwan IBI versus Karr's IBI
are the use of all insectivores and consideration of numbers of hybrids or exotic species rather than the
proportion of hybrids. Exotic species are species that are present in a region through introduction by
man or have recent invasions that would not have been possible without human intervention. The total
IBI scores then yield the following biological conditions categories: Non-impaired 35 - 45, Slightly
impaired 23 - 34, Moderately impaired 15 - 22, and Severely impaired 0 - 14.

T able 10.4 Index of Biological Integrity (IBI) for Taiwan (after Hu et al., 2005)

Scoring criteria

Category Metrics

5 3 1

Species richness and
composition

1. Total number of fish species

ı 10

4-9 0-3

2. Number of darter species ı 3 1-2 0

3. Number of sunfish species ı 2 1 0

4. Number of suckers species ı 2 1 0

5. Number of intolerant species

ı 3

1-2 0

Trophic composition 6. Proportion of individuals as omnivores < 60% 60%-80% > 80%

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

Fish abundance and
condition

8. Number of individuals in sample ı 101 51-100 0-50

9. Number of hybrids or exotic species 0 1 ı 2

Karr's IBI and its many regional modifications for areas throughout the U.S. and around the world
have generally been well calibrated to small “wadable” streams, but applications in larger rivers are less
common (Lyons et al., 2001). Lyons et al. (2001) identified 7 IBIs developed for use in large rivers, and
then developed IBIs for use in large rivers in Wisconsin. In this case large rivers are defined as having at