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Quantitative indicators of biological integrity are needed for streams in the Great Plains of North America, but it was not known whether the index of biotic integrity (IBI) approach would be effective in this semiarid region. Great Plains streams have a depauperate and tolerant ichthyofauna and highly variable physicochemical conditions that may mask the effects of non‐point‐source pollution and stream habitat degradation. We developed an IBI based on fish assemblages by screening metrics for range, responsiveness to human influence, precision, and lack of redundancy; we then tested the IBI's ability to detect anthropogenic effects by validating the index with an independent data set. The IBI was composed of 10 metrics based on species richness and composition, trophic and reproductive guilds, and age structure. These 10 metrics had many significant correlations with substrate and water chemistry variables but had fewer significant correlations with riparian condition and watershed variables. Of the watershed variables, road density had the highest number of significant correlations with final IBI metrics. The IBI was validated by demonstrating its responsiveness to aggregate measures of human influence, site‐level habitat, and water chemistry, and its lack of responsiveness to factors that varied naturally, such as stream size and site elevation. The IBI was also temporally stable within and between years during repeat visits to a subset of sampled reaches. This IBI can be used as a measure of biological integrity for management of prairie streams faced with threats such as introduced species, intensive agriculture, grazing, and coalbed natural gas extraction. Although we developed this IBI based on data from Montana prairie streams only, our IBI can probably serve as a framework for other North American plains streams and our results suggest that the IBI approach may be useful in other semiarid regions of the world.

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We applied the index of biotic integrity (IBI) to the portion of the Arkansas River basin within the Southwestern Tablelands ecoregion, located on the Great Plains of southeastern Colorado. Only nine IBI metrics were appropriate for this region, largely because of the depauperate and tolerant ichthyofauna. The modified index was then used to assess effects of U.S. Army mechanized infantry training on biotic integrity of the Purgatoire River at 12 sites adjacent to the Pifion Canyon Maneuvers Site, a remote and relatively undisturbed canyon reach on a seventh‐order Arkansas River tributary. Decrease in abundance of adult red shiners Cyprinella lutrensis, a tolerant omnivorous species, over a 6‐year period (1983–1989) caused marked increases in the IBI at 9 of 12 sites despite lack of obvious changes in environmental quality after training began in 1985. Neither sampling variation nor the magnitude and timing of floods were sufficient to explain the large decrease in red shiner abundance. Other attributes of the biota, such as presence of long‐lived fishes and lack of introduced species, provided no evidence for detrimental change. The majority of potential IBI metrics were hampered by the low fish species richness, the preponderance of trophic and habitat generalists, or other attributes of the depauperate ichthyofauna. Moreover, human perturbations that cause change in fish communities of midwestern U.S. streams are suspected in many cases to mimic natural disturbances in this system, so they may have relatively little effect. Conversely, some perturbations considered benign in more mesic environments are likely to cause dramatic changes. We therefore propose that our understanding of the structure, function, and natural variation of fish communities in western Great Plains streams must increase substantially before we can define fully appropriate measures of biotic integrity for these lotic systems.

The movement of juvenile salmonids between small tributaries and main‐stem habitats in southeast Alaska watersheds is poorly understood. We observed movements of steelhead Oncorhynchus mykiss, coho salmon O. kisutch, and Dolly Varden Salvelinus malma between main‐stem and tributary habitats at weirs located on tributaries in the Staney Creek watershed in southeast Alaska. We used seasonal relative abundance (catch per unit effort) in eight main‐stem reaches and eight tributaries to corroborate observed movement in the two streams with weirs. We observed juvenile steelhead and coho salmon moving through the weirs into tributaries during the fall as flows increased and temperatures decreased. The relative abundance of steelhead was greater in main‐stem sites than in tributaries during the summer, whereas during spring and fall relative abundance in the tributaries was similar to that in the main stem. Juvenile coho salmon were abundant in tributaries during all seasons. The relative abundance of Dolly Varden was greater in the tributaries than in the main‐stem during all seasons. These results underscore the significance of links between main‐stem habitats and small tributaries for production of juvenile salmonids.

Coal bed natural gas (CBNG) development in the Powder River geologic basin (PRGB) may alter water quality, quantity, or aquatic habitats. CBNG product water is generally higher than surface waters in dissolved sodium and bicarbonate and sometimes exceeds toxicity levels for fathead minnows and daphnids. Montana and Wyoming water quality standards do not account for differential ion toxicity; toxicity data for most fishes of the PRGB are lacking, and there are minimal data available on composition of CBNG product water. One field study suggests that CBNG may limit fish distribution. Metals and trace elements in CBNG product water, wetlands, impoundments, sediments, and biological tissues may exceed chronic standards or other biologically relevant thresholds. Product-water dissolved oxygen, pH, and turbidity are comparable to surface waters, but spatiotemporal temperature variation may disrupt natural cues. Increased discharge from CBNG product-water discharge or groundwater depletion may alter the ecology of PRGB streams. Indirect effects may occur if development alters food webs, plant communities, or aquatic habitats. Road construction may increase sedimentation, and stream crossings may fragment fish populations. Impoundments may be a source of non-native fish species. The uncertainty concerning potential effects of CBNG development on fish in the PRGB highlights the need for further research and monitoring.

1. Extraction of coalbed natural gas (CBNG) often results in disposal of large quantities of CBNG product water, which may affect aquatic ecosystems. We evaluated the effects of CBNG development on fish assemblages in tributary streams of the Powder and Tongue rivers. We used treatment and control, impact versus reference sites comparisons, surveys of CBNG product-water streams and in situ fish survival approaches to determine if CBNG development affected fish assemblages. 2. Several of our results suggested that CBNG development did not affect fish assemblages. Species richness and index of biotic integrity (IBI) scores were similar in streams with and streams without CBNG development, and overall biotic integrity was not related to the number or density of CBNG wells. Fish occurred in one stream that was composed largely or entirely of CBNG product water. Sentinel fish survived in cages at treatment sites where no or few fish were captured, suggesting that factors such as lack of stream connectivity rather than water quality limited fish abundance at these sites. Fish species richness did not differ significantly from 1994 to 2006 in comparisons of CBNG-developed and undeveloped streams. Biotic integrity declined from 1994 to 2006; however, declines occurred at both impact and reference sites, possibly because of long-term drought. 3. Some evidence suggested that CBNG development negatively affected fish assemblages, or may do so over time. Specific conductivity was on average higher in treatment streams and was negatively related to biotic integrity. Four IBI species richness metrics were negatively correlated with the number or density of CBNG wells in the catchment above sampling sites. Bicarbonate, one of the primary ions in product water, was significantly higher in developed streams and may have limited abundance of longnose dace (Rhinichthys cataractae). Total dissolved solids, alkalinity, magnesium and sulphate were significantly higher in developed streams. 4. Biological monitoring conducted before the development of CBNG, and continuing through the life of development and reclamation, together with data on the quantity, quality and fate of CBNG product water will allow robust assessment of potential effects of future CBNG development worldwide.

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