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Title: Effects of surface water withdrawal on fishes in rivers of northeast Louisiana
Authors: Killgore, K. Jack
Douglas, Neil H.
Keywords: Fishes--Ecology
Water use--Louisiana--Environmental aspects
Publisher: Environmental Laboratory (U.S.)
U.S. Army Engineer Waterways Experiment Station.
Series/Report no.: Technical Report;EL-88-2
Abstract: Water demands for crop irrigation and commercial fish farming are increasing in northeast Louisiana. Withdrawal of surface water from the rivers is being considered as one alternative to alleviate the water shortage during the summer and fall months. Relationships between fish abundance and water volume were determined from data collected at 15 sites in northeast Louisiana and used to estimate changes in fish abundance resulting from various surface water withdrawal scenarios. For most scenarios, water demands exceeded the water supply for 1 or more months resulting in a 100-percent loss of fishes due to dewatering effects, migration from the area, and a severe reduction in habitat quality. Approximately 70 percent of the fishes lost were minnows/darters and juvenile shad, followed by juvenile sunfishes (20 percent) and harvestable sport and commercial fishes (10 percent). In addition to water volume, the influence of other physical and chemical variables on fish abundance was evaluated using stepwise multiple regression, Variability in fish abundance was best explained by water volume, dissolved oxygen, and conductivity (R² = 0.77). Other variables (pH, water depth, percent cover, temperature, turbidity, water velocity, and discharge) had no significant influence on increasing the predictive capability of the regression equation. Although changes in dissolved oxygen and conductivity may accompany decreases in water volume, the ability to make these predictions as part of an impact assessment was beyond the scope of this study. However, these variables should be considered as potential limiting habitat factors in rivers of northeast Louisiana during the summer and early fall months and can provide a basis of monitoring habitat quality under actual surface water withdrawal conditions. An index of biotic integrity (IBI) was used to compare the quality of the existing fish community structure between study sites, The IBI can be incorporated in a management plan to identify both pristine and degraded habitat conditions, but is not intended as a predictive technique to estimate changes in fish abundance for future conditions. The IBI integrates attributes of species richness and composition, trophic composition, and fish abundance to rate the fish community structure as excellent, fair, or poor. In northeast Louisiana, poor habitat conditions are usually associated with high numbers of juvenile shad, while excellent habitat is dominated by minnows, shiners, and darters. Bayou Bartholomew was the only major river in the study area that consistently exhibited high species richness, trophic composition representative of undisturbed habitat, and a relatively high number of total fishes compared with other rivers in northeast Louisiana. High quality fish habitats that do exist in other rivers, such as gravel substrate, continuous flowing water, and high amounts of instream cover, are intermittent and uncommon and are usually associated with small tributaries or are below water-control structures. Bayou Bartholomew is one of the few remaining water bodies in northeast Louisiana that is considered an ecologically significant stream because of its high diversity of stream-dwelling fish species.
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