Index Of Biotic Integrity Scores Research Articles

Bioassessment of Fish Communities of the Upper Delaware River

We assessed the biotic integrity of the middle-to-upper Delaware River. We sampled fish and assembled water quality data for eight stations and three habitat types (pool, riffle, and submerged aquatic vegetation [SAV]) of the Delaware River and applied an existing index of biotic integrity (IBI) recently developed for the northern mid-Atlantic slope drainages. We used Spearman's correlation to test IBI scores against measures of water quality (WQI) and cultural pollution. IBI scores were not significantly correlated with WQI, but were significantly negatively correlated with sewage load of adjacent tributaries (rs = −0.647, p = 0.08). Sites ranged from good to fair in biotic integrity. Fish assemblage composition from all three habitat types was necessary in order to accurately characterize biotic integrity. Of the three habitat types, fish assemblages from SAV habitats had the greatest positive effect on biotic integrity. Continued application of the IBI may be useful as a long-term monitoring tool as this river corridor becomes increasingly urbanized.

Application of the Index of Biotic Integrity Methodology to New Zealand Freshwater Fish Communities

An index of biotic integrity (IBI) was developed for freshwater fish in New Zealand streams. Data on freshwater fish occurrence for 5497 sites over the entire country were obtained from the New Zealand freshwater fish database for the period 1980-2002. Environmental habitat descriptors for the stream watersheds above or at each of these sites were obtained from an existing river environment classification using a geographic information system. Of the many IBI metrics in use globally, only six were adapted and applied because of differences between the fish fauna of New Zealand and the United States. A number of evaluation methods showed that all six metrics contributed to the overall IBI scores with high levels of consistency. The IBI assessment of sites sampled at different times showed high levels of temporal concordance. The IBI scores differed significantly among the geological areas, the sampling method used, and the year of survey. Overall, the results presented demonstrate the potential for New Zealand freshwater fish to be used to assess river condition at large spatial scales in New Zealand in the absence of specifically selected reference sites. This application demonstrates the effectiveness of the IBI approach even with a fauna of limited diversity and limited ecological specialisation as in the New Zealand fish fauna.

Using an IBI to assess effectiveness of mitigation measures to replace loss of a wetland-stream ecosystem

Approximately 7.3 hectares of wetlands, composed of six separate cells, were created to mitigate the loss of a 6-hectare, beaver-influenced, wetland-stream complex destroyed by the construction of a multipurpose impoundment in the Cedar Run watershed in Fauquier County, Virginia, USA. The mitigation action physically replaced the lost wetlands and was judged successful in meeting planned objectives and regulatory requirements (which did not include standards for biota). A pre-project fish survey conducted in 1974 in the wetland-stream complex and three nearby streams provided a baseline condition from which to assess project impacts on fish, as determined from yearly surveys in the cells and the stream reach immediately upstream. In addition, fish communities were sampled at 157 stream locations within the northern Virginia Piedmont from 1997 to 1999 to establish a regional Index of Biotic Integrity (IBI) based on fish assemblages. A modification of that IBI was developed to assess the effectiveness of the mitigation based on 22 stream segments that were heavily influenced by beaver. Pre- and post-project conditions were assessed by gauging them against the wetland-stream complexes using this IBI. The IBI score for the mitigation area dropped from the pre-project 34 to 18 the first year after construction and ranged from 18 to 28 over the ten-year post-project monitoring period. A reduction in the number of native species was observed, and there was a dramatic shift in composition and relative abundance within key species groups. In general, the mitigation benefited species favoring lentic environments over those preferring lotic environments and had negative effects on trophic and habitat specialists and less tolerant species. Scores for the mitigation cells were lower than scores for the original wetlands for the following IBI metrics: number of darter species, number of minnow species, percent of the assemblage comprised of the single most dominant species, percent of tolerant individuals, percent of benthic invertivores, and percent of specialist carnivores minus tolerants. Upstream reach IBI scores also diminished over the same 10-year period, although more gradually. The IBI showed that, despite meeting all regulatory requirements, the mitigation failed to replace the original fish community in the wetland-stream complex and adversely impacted additional stream habitat. Using tools such as an IBI to monitor biological condition can help planners effectively mitigate unavoidable project impacts and avoid the unintended loss of important natural resources caused by compensatory mitigation actions.

URBANIZATION INFLUENCES ON AQUATIC COMMUNITIES IN NORTHEASTERN ILLINOIS STREAMS1

ABSTRACT: Biotic indices and sediment trace element concentrations for 43 streams in northeastern Illinois (Chicago area) from the 1980s and 1990s were examined along an agricultural to urban land cover gradient to explore the relations among biotic integrity, sediment chemistry, and urbanization. The Illinois fish Alternative Index of Biotic Integrity (AIBI) ranged from poor to excellent in agricultural/rural streams, but streams with more than 10 percent watershed urban land (about 500 people/mi2) had fair or poor index scores. A macroinvertebrate index (MBI) showed similar trends. A qualitative habitat index (PIBI) did not correlate to either urban indicator. The AIBI and MBI correlated with urban associated sediment trace element concentrations. Elevated copper concentrations in sediment occurred in streams with greater than 40 percent watershed urban land. The number of intolerant fish species and modified index of biotic integrity scores increased in some rural, urbanizing, and urban streams from the 1980s to 1990s, with the largest increases occurring in rural streams with loamy/sandy surficial deposits. However, smaller increases also occurred in urban streams with clayey surficial deposits and over 50 percent watershed urban land. These data illustrate the potentially complex spatial and temporal relations among biotic integrity, sediment chemistry, watershed urban land, population density, and regional and local geologic setting.

Habitat Influence on Fish Community Assemblage in an Agricultural Landscape in Four East Central Indiana Streams

ABSTRACT The objective of this study was to relate the quality of the fish community with habitat using the Index of Biotic Integrity (IBI) and Qualitative Habitat Evaluation Index (QHEI) in four agriculturally influenced streams in east central, Indiana. A total of 48 species was collected from 42 sites. IBI scores ranged from 14 to 48, and QHEI scores ranged from 29 to 83. There was a significant positive correlation between IBI and QHEI scores. Furthermore, we found significant positive correlations between IBI scores and four individual QHEI metrics (channel morphology, substrate, poollglide and riffletrun quality, and in-stream cover). Habitat influenced the fish assemblages with channelization and substrate being the primary structuring factors. The land use in this area is 70% agriculture, which has heavily influenced lotic character through anthropogenic practices.

A provisional fish index of biotic integrity for assessing Ouachita Mountains streams in Arkansas, U.S.A.

Multimetric indices are often used to monitor aquatic-resource conditions. We used existing fish-collection data from streams to develop an Index of Biotic Integrity (IBI), which is a multimetric index, for the Ouachita Mountains ecoregion in Arkansas, U.S.A. Each fish-collection site was categorized as reference or non-reference. We examined 62 candidate IBI metrics, and selected 12 non-redundant metrics that differentiated best between reference and non-reference sites. The selected metrics were: Percent (of individuals) as Black Bass; Percent as Benthic Feeders; Percent as Centrarchids; Percent as Cyprinids; Percent as Ictalurids; Percent as Mineral, Site-Prep Spawners; Percent as Mineral, Site-Prep, Parental-Care Spawners; Percent as Simple, Mineral Substrate Spawners; Percent as Miscellaneous, Site-Prep, Parental-Care Spawners; Total Number of Centrarchid Species; Total Number of Arkansas Department of Environmental Quality (ADEQ) Ouachita Mountains Indicator Species; and Total Number of ADEQ Ouachita Mountains Key Species. We standardized each metric to score from 0 to 10 by using linear equations and threshold limits. Some selected IBI metrics had their scoring criteria adjusted to account for watershed size (i.e., stream size). We standardized the IBI to score from 0 to 100. In addition, we determined that our Percent as Black Bass and Percent as Benthic Feeders metrics contributed most to IBI scores in reference conditions, but their contributions decreased with decreasing stream conditions. Reproductive metrics contributed most in degraded stream conditions. Furthermore, we identified relations between IBI metrics and water-quality and land-use variables; some relations were counterintuitive. Unexpected relations may be random observations explained by limited ranges of land-use and water-quality variables. When select water-quality and land-use variables were included in a principal component analysis, a composite Land Use Intensity variable explained most of the model variance. Although the IBI has not been independently validated, the PCA, as well as other superficial analyses, indicated that the IBI should be able to differentiate stream conditions.

Effect of Electrofishing Effort on an Index of Biotic Integrity

Abstract We sampled fishes at 15 stream sites in the Ozark Highlands ecoregion of Arkansas and examined the effects of sampling effort on an index of biotic integrity (IBI). We found that sampling effort affected component metric scores, IBI scores, and qualitative site classifications. The scores of taxonomic richness metrics increased with increasing effort, while relative abundance metrics were inconsistently affected by sampling effort. The scores of all metrics stabilized with increasing effort. Although some deviation from the sampling effort designated for the IBI appeared acceptable, we found that even a sampling effort deviation of 10 mean stream widths from the designated effort (19.6%) caused one qualitative site classification to change. Our results showed that differences in sampling effort can affect IBI scores and result in erroneous stream assessments. They also indicated that an accurate assessment of regional stream conditions relies on incorporating the specific sampling effort designat...

Impacts of Urban Land Cover on Trout Streams in Wisconsin and Minnesota

We examined relations between the amounts and spatial patterns of urban land cover and fish assemblages, physical habitat, base flow, and water temperature at 39 sites in small, coldwater trout streams in Wisconsin and Minnesota. The amount of connected impervious surface area in the watershed was negatively correlated with a fish-based coldwater index of biotic integrity (IBI), catches of all coldwater and coolwater fishes and trout, and the percentage of intolerant fish; it was positively correlated with fish species richness and the percentage of tolerant fish. Nonlinear models were developed by means of 90% quantile regression to predict the maximum possible IBI score, abundance of trout, and percentage of intolerant fish at a given level of imperviousness. At a connected imperviousness of less than about 6% for a watershed, all three variables could have high values, whereas at a connected imperviousness above 11% the values were inevitably low. Between 6% and 11%, minor changes in urbanization could result in major changes in stream fishes. Canonical correspondence analysis identified water temperature and base flow as the key instream habitat factors explaining stream fish assemblages patterns. The percentage of connected impervious area in the watershed had a positive, linear relation with water temperature and a negative, nonlinear relation with base flow, suggesting pathways by which urbanization affected fish assemblages. Partial redundancy analysis indicated that land cover within 30 m of the stream channel explained considerably more variance in fish assemblages and instream habitat and physical conditions than land cover beyond 30 m. Our study suggests that low levels of urban development can damage coldwater stream systems. Development strategies that protect the riparian area and minimize imperviousness may reduce this damage.

Regions of High Fish Diversity for Conservation Concern within the U.S. Central Plains

ABSTRACT Fish samples from 300 stream sites in Nebraska, Kansas, and Missouri were used to identify potential conservation areas based on (a) number of endemic species, (b) number of threatened and endangered species, c) Index of Biotic Integrity scores, and d) species/family richness. Three areas emerged as potential high-priority conservation areas—the Ozark plateau, south-central Kansas and the Nebraska Sand Hills. The techniques used here can highlight watersheds and streams of potential management concern.

AN INDEX OF BIOTIC INTEGRITY FOR FISH ASSEMBLAGES IN OZARK HIGHLAND STREAMS OF ARKANSAS

We developed an Index of Biotic Integrity (IBI) for wadeable Ozark Highland streams in Arkansas by using fish-assemblage data from 96 stream sites. All sites were classified as reference or non-reference based on both subjective and objective information, and we used uni- and bivariate statistics to examine 39 potential IBI metrics. Seven metrics were chosen for the IBI. They were percent (of individuals) as algivorous/herbivorous, invertivorous, and piscivorous; percent with black spot or an anomaly; percent green sunfish Lepomis cyanellus, bluegill L. macrochirus, yellow bullhead Ameiurus natalis, and channel catfish Ictalurus punctatus; percent invertivorous; percent top carnivores; number of darter Etheostoma and Percina, sculpin Cottus, and madtom Noturus species; and number of lithophilic spawning species. Trophic metrics contributed most to IBI scores, and metrics were most often correlated with chloride, nutrient, land use, road density, and sedimentation levels, which suggests that our IBI should be able to successfully differentiate stream conditions in wadeable Ozark Highland streams of Arkansas.

Index of Biotic Integrity Utility for the Fishery of the James River of the Dakotas

ABSTRACT Twenty-two metrics were evaluated and used to modify an index of biotic integrity (IBI) to assess the fish community health of five regions within the James River watershed of North Dakota and South Dakota. Pearson correlation coefficients, scatter plots, principal component analysis, and Kendall's tau were used to examine metric redundancy, response, and contribution to IBI scores. Only four metrics were strongly correlated with one other metric (r≥ 0.90). About half the metrics displayed an increasing or decreasing linear response to biotic integrity. The first two principal components accounted for 69 to 86% of the variance in the five regions of the basin. All metrics contributed to the IBI score throughout the basin, except for five metrics at upper river sites. Low species richness resulted in poor performance by most metrics for the upper 435-km North Dakota portion of the basin; however, the IBI does appear to be a useful biomonitoring tool for the lower 760-km South Dakota portion of the basin.

Development of a Fish-Based Index of Biotic Integrity for Small Inland Lakes in Central Minnesota

We developed a fish-based index of biotic integrity (IBI) for a set of Minnesota lakes having similar geophysical and chemical features. Fish data were collected by means of trap nets, gill nets, shoreline seines, and backpack electrofishing. Of 30 evaluated metrics, we identified 16 metrics of three types: species richness, community assemblage, and trophic composition. In contrast to lotic IBIs, where a single sampling gear is usually used, data from all four sampling gears were necessary for IBI development. We selected metrics based on responses to measures of human-induced stress based on watershed land use patterns and human population density. Species richness and community composition metrics describing intolerant or habitat specialist species were most sensitive to differences in human-induced stress. Because these species were found in the nearshore zone of lakes, effective sampling of the nearshore fish community was essential to the development and performance of the IBI. Trap-net- and gill-net-based metrics, however, were essential to the development of trophic composition metrics, the trap nets providing the best insectivore and omnivore metric and the gill nets providing the best top carnivore metrics. Lake IBI scores reflected differences in land use patterns, trophic state, and aquatic vegetation. Sensitivity analysis indicated that selected metrics contributed to IBI performance, but the relative contribution of individual metrics varied among human-induced stress categories. Additional work is needed to test the performance of this IBI on an independent group of lakes, to set the range of applicability, and to determine the effectiveness of the IBI as an assessment tool for lakes.

Hydrologic variability and the application of Index of Biotic Integrity metrics to wetlands: A great lakes evaluation

Interest by land-management and regulatory agencies in using biological indicators to detect wetland degradation, coupled with ongoing use of this approach to assess water quality in streams, led to the desire to develop and evaluate an Index of Biotic Integrity (IBI) for wetlands that could be used to categorize the level of degradation. We undertook this challenge with data from coastal wetlands of the Great Lakes, which have been degraded by a variety of human disturbances. We studied six barrier beach wetlands in western Lake Superior, six drowned-river-mouth wetlands along the eastern shore of Lake Michigan, and six open shoreline wetlands in Saginaw Bay of Lake Huron. Plant, fish, and invertebrate communities were sampled in each wetland. The resulting data were assessed in various forms against gradients of human disturbance to identify potential metrics that could be used in IBI development. Our results suggested that the metrics proposed as potential components of an IBI for barrier beach wetlands of Lake Superior held promise. The metrics for Lake Michigan drowned-river-mouth wetlands were inconsistent in identifying gradients of disturbance; those for Lake Huron open embayment wetlands were yet more inconsistent. Despite the potential displayed by the Lake Superior results within the year sampled, we concluded that an IBI for use in Great Lakes wetlands would not be valid unless separate scoring ranges were derived for each of several sequences of water-level histories. Variability in lake levels from year to year can produce variability in data and affect the reproducibility of data collected, primarily due to extreme changes in plant communities and the faunal habitat they provide. Substantially different results could be obtained in the same wetland in different years as a result of the response to lake-level change, with no change in the level of human disturbance. Additional problems included limited numbers of comparable sites, potential lack of undisturbed reference sites, and variable effects of different disturbance types. We also evaluated our conclusions with respect to hydrologic variability and other major natural disturbances affecting wetlands in other regions. We concluded that after segregation of wetland types by geographic, geomorphic, and hydrologic features, a functional IBI may be possible for wetlands with relatively stable hydrology. However, an IBI for wetlands with unpredictable yet recurring influences of climate-induced, long-term high water periods, droughts, or drought-related fires or weather-related catastrophic floods or high winds (hurricanes) would also require differing scales of measurement for years that differ in the length of time since the last major natural disturbance. A site-specific, detailed ecological analysis of biological indicators may indeed be of value in determining the quality or status of wetlands, but we recommend that IBI scores not be used unless the scoring ranges are calibrated for the specific hydrologic history pre-dating any sampling year.

Development of a Stream Habitat Index for the Northern Lakes and Forests Ecoregion

Physical habitat was quantified in 105 randomly selected streams across the Northern Lakes and Forests Ecoregion during 1998 and 1999 to develop a stream habitat index for the region. Physical habitat measures (106) were classified into four groups: substrate, instream cover, riparian zone–land use, and geomorphology–hydrology. Variable reduction procedures yielded seven variables: sinuosity, percent of substrate gravel or larger, percent substrate as detritus or muck, percent of bank with forested cover, amount of bank erosion, number of large logs per 100 m, and mean length of pools. Streams were separated by a gradient value of 3 m/km (low N = 70; high N = 35) and assigned to model and test data sets. For low-gradient streams in the model data set, the seven habitat variables explained 47% of the variation in index of biotic integrity (IBI) scores. To produce the habitat index, the coefficients in the regression were used to weight each of the seven variables. For low-gradient streams in the test data set, the habitat index explained 20% of the variation in IBI scores. A habitat index could not be developed for high-gradient sites, probably due to the low number of sites. Comparison of habitat to IBI scores provides resource managers with a method to evaluate the contribution of habitat quality to the IBI score.

RELATION BETWEEN FISH COMMUNITIES AND RIPARIAN ZONE CONDITIONS AT TWO SPATIAL SCALES1

ABSTRACT: The relation offish community composition to riparian cover at two spatial scales was compared at 18 streams in the agricultural Minnesota River Basin. The two spatial scales were: (1) local riparian zone (a 200 meter wide buffer extending 2 to 3 kilometers upstream of the sampling reach); and (2) the upstream riparian zone (a 200 m wide buffer on the mainstem and all perennial tributaries upstream of the sampling reach). Analysis of variance indicated that streams with wooded‐local riparian zones had greater fish species richness (means = 20 and 15, respectively) and Index of Biotic Integrity (IBI) scores (means = 40 and 26, respectively) than streams with open‐local riparian zones. Streams with wooded‐upstream riparian zones tended (were not statistically significant) to have greater numbers of species (means = 19 and 15, respectively) and IBI scores (means = 33 and 28, respectively) than streams with open‐upstream riparian zones. There was no significant interaction between the riparian zone conditions at the two scales. This study suggests that maintenance of wooded riparian cover along streams could be effective in maintaining or improving fish community composition in streams draining heavily agricultural areas.

The Impact of Above Grade Sewerline Crossings on the Distribution and Abundance of Fishes in Recovering Small Urban Streams of the Upper Ohio River Valley

ABSTRACT The distribution and abundance of fishes along four small urban streams in western Pennsylvania and northern West Virginia were examined. The water quality of three of these streams was moderately to severely degraded along various reaches. While resident fish communities in the degraded streams were depauperate, reaches with access were nonetheless routinely used by transient species from the nearby navigation system. Species richness and biomass of the fish communities dropped abruptly upstream of above grade, concrete-encased sewerline crossings. Similar abrupt declines in diversity and biomass were also apparent upstream of a sewerline crossing in a nondegraded stream with a high quality fishery. Where access for transient fishes from larger downstream waters was denied, index of biotic integrity scores declined by 26% to 43%, and species diversity declined by 39% to 69%. Also, partly because of the tendency for the transients to be larger than resident fishes of small streams, there was a biomass reduction between downstream and upstream sites of 81% to 87%.

Impacts of urbanization on stream habitat and fish across multiple spatial scales.

We analyzed the relation of the amount and spatial pattern of land cover with stream fish communities, in-stream habitat, and baseflow in 47 small southeastern Wisconsin, USA, watersheds encompassing a gradient of predominantly agricultural to predominantly urban land uses. The amount of connected impervious surface in the watershed was the best measure of urbanization for predicting fish density, species richness, diversity, and index of biotic integrity (IBI) score; bank erosion; and base flow. However, connected imperviousness was not significantly correlated with overall habitat quality for fish. Nonlinear models were developed using quantile regression to predict the maximum possible number of fish species, IBI score, and base flow for a given level of imperviousness. At watershed connected imperviousness levels less than about 8%, all three variables could have high values, whereas at connected imperviousness levels greater than 12% their values were inevitably low. Connected imperviousness levels between 8 and 12% represented a threshold region where minor changes in urbanization could result in major changes in stream condition. In a spatial analysis, connected imperviousness within a 50-m buffer along the stream or within a 1.6-km radius upstream of the sampling site had more influence on stream fish and base flow than did comparable amounts of imperviousness further away. Our results suggest that urban development that minimizes amount of connected impervious surface and establishes undeveloped buffer areas along streams should have less impact than conventional types of development.

WATERSHED URBANIZATION AND CHANGES IN FISH COMMUNITIES IN SOUTHEASTERN WISCONSIN STREAMS1

ABSTRACT: We compared watershed land‐use and fish community data between the 1970s and 1990s in 47 small streams in southeastern Wisconsin. Our goal was to quantify effects of increasing urbanization on stream fishes in what had been a predominantly agricultural region. In the 43 test watersheds, mean surface coverage by agricultural lands decreased from 54 percent to 43 percent and urban lands increased from 24 percent to 31 percent between 1970 and 1990. Agriculture dominated the four reference watersheds, but neither agriculture (65–59 percent) nor urban (4.4–4.8 percent) land‐uses changed significantly in those watersheds during the study period. From the 1970s to the 1990s the mean number of fish species for the test stream sites decreased 15 percent, fish density decreased 41 percent, and the index of biotic integrity (IBI) score dropped 32 percent. Fish community attributes at the four reference sites did not change significantly during the same period, although density was substantially lower in the 1990s. For both the 1970s and 1990s test sites, numbers of fish species and IBI scores were positively correlated with watershed percent agricultural land coverage and negatively correlated with watershed urban land uses, as indexed by percent effective connected imperviousness. Numbers of fish species per site and IBI scores were highly variable below 10 percent imperviousness, but consistently low above 10 percent. Sites that had less than 10 percent imperviousness and fewer than 10 fish species in the 1970s suffered the greatest relative increase in imperviousness and decline in species number over the study period. Our findings are consistent with previous studies that have found strong negative effects of urban land uses on stream ecosystems and a threshold of environmental damage at about 10 percent imperviousness. We conclude that although agricultural land uses often degrade stream fish communities, agricultural land impacts are generally less severe than those from urbanization on a per‐unit‐area basis.

Considerations regarding development of index of biotic integrity metrics for large rivers

The index of biotic integrity (IBI) is the most widely used multi-metric index to assess the biological health of fish communities. Numerous state-specific or basin-specific versions of the IBI have been developed for wadeable streams. However, progress has been considerably slower with regard to developing IBIs for large rivers. Sampling in large rivers presents a number of unique problems, many of which result from the size of the waterbody to be sampled. Topics covered in this paper include several related to field sampling such as electrofishing output requirements, day vs night sampling effectiveness, effectiveness of various gears and overlap among them, the lack of reference sites in large rivers, seasonal movements of fishes, variables affecting sampling efficiency, sampling effort, and QA/QC. Also discussed are several topics related to data analysis such as data variability, influence of YOY fishes on catch results, minimum size of the data set, metric calibration, proper characterization of trophic guilds, and establishment of tolerant/intolerant species. Before meaningful IBI scores can be generated, new metrics, applicable to large rivers, need to be developed. Based on the considerations discussed in this paper, it is recommended that large rivers be sampled by a combination of seining and electrofishing, with the electrofishing being conducted at night and with an effort of ≥500 m.

Using historical biological data to evaluate status and trends in the Big Darby Creek watershed (Ohio, USA)

AbstractAssessment of watershed ecological status and trends is challenging for managers who lack randomly or consistently sampled data, or monitoring programs developed from a watershed perspective. This study investigated analytical approaches for assessment of status and trends using data collected by the Ohio Environmental Protection Agency as part of state requirements for reporting stream quality and managing discharge permits. Fish and benthic macroinvertebrate metrics collected during three time periods (1979–1981, 1986–1989, 1990–1993) were analyzed for the mainstem of Big Darby Creek, a high‐quality warm‐water stream in central Ohio, USA. Analysis of variance of transformed metrics showed significant differences among time periods for six fish metrics. In addition, significant positive linear trends were observed for four metrics plus the index of biotic integrity score, and negative linear trends for two fish metrics. An analysis of a subset of sites paired by location and sampled over the three periods reflected findings using all available data for the mainstem. In particular, mean estimates were very similar between the reduced and full data sets, whereas standard error estimates were much greater in the reduced subset. Analysis of serial autocorrelation patterns among the fish metrics over the three time periods suggests changes in the nature of stressors over time. A comparison within the most recent time period showed significantly better condition for Big Darby Creek mainstem than for Hellbranch Run (the easternmost subwatershed), after adjusting for watershed size. The consistency of paired and nonrandomized results suggested that either type of data might be judiciously used for this watershed assessment. Results indicated that overall biological condition of the mainstem of the Big Darby Creek watershed has significantly improved since the early 1980s.