The Fish Index of Biotic Integrity (FIBI) is a composite index in which several individual metrics are combined to provide a community-level assessment of stream biological conditions.The FIBI contains twelve metrics that relate to species/taxa richness, balance, and the proportion of individuals belonging to specific feeding and habitat groups. The FIBI also contains a fish abundance metric and a fish health condition metric.
The FIBI was developed from a data base of 100 stream reference sites and 55 test sites located in eight ecological regions (Ecoregion) of Iowa.The sites were sampled between 1994 and 1998. Reference sites were chosen to represent least impacted stream habitats in the ecoregions in which they are located.Test sites were chosen to represent common types of stream impacts (e.g., point source discharge; riparian livestock grazing), or they were chosen as part of a watershed assessment project.
The FIBI metrics were developed and calibrated using data from warm-water streams only.The response of several metrics to changes in stream quality is different in cold-water streams, particularly with respect to species richness metrics, and application of these metrics in cold-water streams may lead to erroneous conclusions about stream condition.Therefore, application of the FIBI is limited to warm-water stream communities. The Iowa DNR is currently developing a methodology to provide an IBI for cold-water streams.
Guidelines have been developed to describe differences at four qualitative levels of fish assemblage integrity.The guidelines represent a general framework for relating fish assemblage attributes that correspond with qualitative ranges of the FIBI. Because there are regional differences in the levels of fish assemblage integrity, the DNR uses a more specific, ecoregion-based approached to assess stream biological integrity.
The first four metrics: native fish species richness, number of sucker species, number of sensitive fish species, number of benthic invertivore species, were calibrated by major river basin (i.e. Mississippi River Basin or Missouri River Basin) in order to account for natural, inter-basin differences in fish species richness. The Missouri River basin contains significantly lower numbers of fish species than the Mississippi River basin. In order to establish realistic reference expectations, separate optimum levels of fish species richness were developed for the two major basins.
Native Fish Species Richness: In warm-water streams, the number of native fish species is expected to decrease with declining stream quality. The presence of a large number of native fish species indicates that stream habitat and water quality are sufficient to meet the diverse needs of many different species. As stream size increases, the optimum level of native fish species richness generally increases. The metric has a broad range of response across streams of varying chemical and physical characteristics.
Exotic fish species like the common carp (Cyprinus carpio) and introduced species can represent a large proportion of the fish assemblage in highly disturbed streams; therefore, these species are not counted. The bluegill (Lepomis macrochirus) and largemouth bass (Micropterus salmoides) are commonly stocked in Iowa’s lakes and farm ponds, and juvenile fish are often found in southern and western Iowa streams where they are not known to successfully reproduce. Because these species can artificially inflate the native fish species metric, bluegill and largemouth bass are classified as introduced species and they are not counted for this metric.
Number of sucker (Catostomidae) species: Fish belonging to the sucker family (Catostomidae) are relatively long-lived, and have an affinity for deeper areas in streams. Several species of suckers are considered habitat specialists because they feed primarily on benthic invertebrates and require silt-free, rock substrates to successfully reproduce. In Iowa’s warm-water streams, the number of sucker species attains the highest level in streams that have good water quality and physical habitat characteristics. As stream size increases, sucker species richness generally increases to the optimum level. The metric has a moderately broad range of response across streams of varying chemical and physical characteristics.
Number of sensitive fish species: As stream conditions deteriorate, fish species that are classified as sensitive fish species decline in abundance and can eventually disappear. Many sensitive species are habitat specialists that are less able to adapt to stream changes affecting their specific habitat niche. Other sensitive species are intolerant of water quality degradation, such as increases in turbidity, nutrient enrichment, and toxins. The metric has a broad range of response across streams of varying chemical and physical characteristics. As stream size increases, sensitive fish species richness generally increases to the optimum level.
Number of benthic invertivore species: Fish species that are classified as benthic invertivores feed predominantly on aquatic insects and other bottom-dwelling macro-invertebrates. The number of benthic invertivore species, reaches its highest level in streams that have abundant and productive benthic habitat. Abundance of benthic invertivore fish is expected to decline in response to habitat alterations or water quality impacts that reduce the availability of benthic macro-invertebrates. As stream size increases, benthic invertivore fish species richness generally increases to the optimum level.
Percentage abundance of three dominant fish species: The proportion of the total number of fish represented by the three most-abundant species is an indicator of balance in the fish assemblage. This metric is inversely related to stream biological health. Healthy warm-water streams have diverse assemblages of fish with the majority of fish distributed somewhat evenly among many species. As stream conditions degrade, an increasingly higher proportion of the total number of fish is represented by a few opportunistic and tolerant fish species. The percent abundance of the three dominant fish species decreases to the optimum level as stream size increases.
Proportion of fish as benthic invertivores: The proportion of fish in the sample that are benthic invertivores is an indicator of benthic habitat quality in terms of producing a food base of aquatic insects and invertebrates for fish. Streams that are impacted by pollution or sedimentation are less likely to support abundant benthic invertebrate populations. The proportion of fish as benthic invertivores is expected to decline in response to deteriorating stream quality.
Proportion of fish as omnivores: The proportion of fish in the sample that are omnivorous (i.e., diet consists of significant quantities of both plant and animal matter, including detritus) is expected to increase in response to deteriorating stream quality. Omnivorous species have generalized feeding habits, and they are able to derive nutritional value from a broad array of food items. Omnivorous fish generally become more abundant in streams that are organically enriched by nutrient and organic matter inputs.
Percent abundance of fish as top carnivores: The proportion of fish in the sample that are top carnivores (i.e., fish constitute a significant part of diet as adults) is an indicator of stream habitat complexity and stability. Top carnivore species often require pools or other areas of concealment such as woody debris snags in order to rest and stalk their prey. Viable populations of minnows and other prey fish must also be present to support large piscivorous fish. The proportion of fish as top carnivores is expected to decline in response to deteriorating stream quality.
Largemouth bass are not included in this metric for the same reason they are not included in the native species count metric. They are commonly stocked and found in streams where they would not normally reproduce, thereby artificially inflating the counts. Therefore they are not included, and listed as trophic level "Largemouth Bass" to highlight this distinction.
Percent abundance of fish as simple lithophilous spawners: The proportion of fish in the sample as simple lithophilous spawners (i.e., fish that lay eggs over rock substrates in streams and provide no paternal care in terms of nest preparation or maintenance) is expected to decline in response to deteriorating stream quality. The reproductive success of simple lithophilous spawners is adversely impacted by sedimentation which fills in the interstitial spaces of rocks where fertilized eggs incubate.
Fish assemblage tolerance index: The fish assemblage tolerance index is a function of the proportion of fish belonging to each of three groupings of species: (1) sensitive species; (2) tolerant species; (3) fish species of intermediate sensitivity to stream degradation. A stream that supports a relatively large proportion of sensitive species and species of intermediate sensitivity will have a lower tolerance index value compared to a stream that is dominated by tolerant fish species. The fish assemblage tolerance index is expected to increase in response to declining stream quality.
Adjusted catch per unit effort: The adjusted catch per unit effort is the number of fish collected per 100 foot length of stream excluding individuals from tolerant species and/or exotic/introduced species. Healthy streams are expected to support good numbers of fish. However, large numbers of tolerant fish species often occur in streams that are organically enriched or disturbed; therefore, fish classified as tolerant species are subtracted from the total catch of fish. Fish abundance can actually reach a maximum at intermediate levels of stream disturbance. Taking this into consideration, a special procedure was used to establish the optimum line for the ADJCPUE metric. The metric values were first plotted against reference site fish index of biotic integrity (FIBI) scores excluding the ADJCPUE metric. The optimum ADJCPUE level was then set equal to the ADJCPUE that was matched or exceeded by 5% of sites with the highest FIBI scores.
IBI Scoring Adjustment
Percent abundance of fish with deformities, eroded fins, lesions, or tumors.
Normally, the proportion of fish having external physical anomalies such as deformities, eroded fins, lesions, and tumors (DELTs), is very low (i.e., <2% of sample) in streams not impacted by identifiable pollution sources. Subtraction adjustments of 5 or 10 points are applied to the final IBI score in cases where the proportion of fish with DELTs exceeds the natural background level of occurrence of these external physical anomalies.