Date of this Version
Regulation and modification of large rivers to accommodate human uses have been a root cause of freshwater biodiversity declines. The Missouri River is among the most drastically-altered large river systems in North America, with a series of mainstem impoundments in the upper watershed altering flow characteristics downstream, and channelization throughout the lower river homogenizing instream habitat and reducing off-channel habitat. Precipitation events during the winter and spring 2010-2011 caused flooding of the greatest magnitude and duration since reservoir completion. The large magnitude and long duration of this flood made it unlike any flood in recent history and provided a unique opportunity to investigate fish response to floodplain connectivity in a regulated river system. Therefore, the objectives of my research were to 1.) compare fish community characteristics across five floodplain sites along the Missouri River, Nebraska, 2.) compare mean stomach fullness, frequency of empty stomachs, condition, size-at-shift to piscivory, and specific diet items consumed by flathead catfish during the flood year in 2011 and non-flood year in 2012, and 3.) use a long-term data set to relate age-0 channel catfish growth rates to environmental conditions in the channelized Missouri River bordering Nebraska. Differences in community structure and composition existed between the uppermost and lowermost sites, and between a middle site and the remaining four sites; however, associations between the fish community and habitat attributes were weak. Flathead catfish had higher mean stomach fullness and condition, lower occurrence of empty stomachs, and began consuming fish and crayfish at about a 150 mm smaller size during the flood year in 2011. Specific diet items differed between years only for smaller flathead catfish with invertebrate-dominated diets. Among the five environmental variables used in the modeling process, growing season duration and low discharge duration were most important in predicting juvenile catfish growth rate. This research provides insight to Missouri River fish community structure, trophic response to hydrological events, and aspects of hydrology that affect first-year fish growth, and should add to the ecological components of future water management in the Missouri River.
Adviser: Mark A. Pegg