Effects of hydrologic variation on dynamics of channel catfish and flathead catfish populations in regulated and unregulated rivers in the southeast USA
Type of DegreeDissertation
Fisheries and Allied Aquacultures
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Altered flow regimes resulting from dam construction can have negative impacts on growth and recruitment of fishes in regulated river systems. The effects of hydrologic variation on channel catfish Ictalurus punctatus and flathead catfish Pylodictis olivaris populations were examined in regulated and unregulated river systems. The objectives of this dissertation were to: 1) develop and validate methods for daily aging age-0 channel catfish, 2) examine the effects of hydrologic variability on growth and hatching success of age-0 channel catfish in regulated and unregulated reaches of the Tallapoosa River Basin, Alabama, and 3) incorporate the effects of variable hydrology on recruitment and variable mortality as stochastic factors influencing the population growth of native and introduced flathead catfish populations from the Coosa (Alabama) and Ocmulgee (Georgia) rivers. In validation studies, mean daily ring counts from sagittal otoliths and known ages of channel catfish were strongly related, indicating that daily ring deposition occurred in the otoliths of age-0 channel catfish. Daily ring counts were accurate for 107 - 119 days post-hatch. In the Tallapoosa River System, growth of age-0 channel catfish was generally highest among age-0 fish from unregulated sites in the Coastal Plain, intermediate among fish from regulated sites in the Piedmont, and lowest among fish from unregulated sites in the Piedmont. All age-0 fish that hatched in September originated from the regulated site, indicating that fish in the regulated reach had a protracted spawning season. Multiple regression models indicated that positive relations existed between growth of age-0 channel catfish and hydrologic variables including mean discharge, minimum discharge, number of high pulses, and rise rate. In addition, growth was negatively affected by high fall rates. Age-0 channel catfish typically hatched during periods with low and stable flow conditions. Size classified matrix models were constructed for native and introduced flathead catfish populations from the Coosa (Alabama, USA) and Ocmulgee (Georgia, USA) rivers, respectively. Recruitment of flathead catfish in the Coosa River was positively related to mean spring discharge and November low flow. In the Ocmulgee River, year-class strength was negatively related to mean March discharge and positively related to June low flow. Incorporation of variable hydrology as a stochastic factor in the matrix model had a negative effect on population growth in the Coosa River. In contrast, incorporation of hydrologic variation as a stochastic factor resulted in stable population growth in the Ocmulgee River. By variably decreasing the mortality of flathead catfish with the highest reproductive values, population growth improved over a 50-year period in the Coosa River. Simulation of increased mortality of harvestable sized flathead catfish in the Ocmulgee River resulted in a substantial decline in population size. Managers are encouraged to use models described in this dissertation as tools in adaptive-flow management programs in the Alabama River System. Specifically, these models can be used to prescribe flow regimes in regulated river systems. Researchers should continually improve models by collecting more data and closely monitoring responses of fish populations to variable flow conditions in regulated river systems.