Spawning and Early Ecology of Riverine Shoal Bass and Largemouth Bass

Abstract

Understanding fish movements and early life-history requirements is important for managing populations because they reflect changing resource needs across the life cycle. Riverine black basses (genus Micropterus) hold significant economic and ecological importance, but knowledge of their reproductive and early life-history requirements is lacking relative to rapidly evolving species designations. Thus, my study objectives were to determine seasonal movement patterns and the factors related to early life-history success of endemic Shoal Bass, M. cataractae, and native Largemouth Bass, M. salmoides, in the lower Flint River catchment, Georgia. Adult black basses were tagged and tracked for 15 months using radio telemetry. I used generalized additive mixed modelling to determine how biotic and environmental factors related to movement patterns. Both species included stationary and mobile individuals with some mobile bass moving greater than 70 km in one direction. Movements increased during the spring which was presumably related to spawning activity. There were numerous locations of fish aggregations during the spring, particularly below a hydropower dam. Shoal Bass females moved longer distances than males. Largemouth Bass moved less during periods of variable discharge. I also collected age-0 Shoal Bass and Largemouth Bass to analyze hatch success and growth using a hurdle model framework and linear regression. Largemouth Bass hatch success was negatively related to water temperature but positively related to increasing discharge. Shoal Bass hatch success was negatively related to discharge variability and was higher during relatively stable flows on the descending limb of the hydrograph. It appears that hydropeaking flows may have affected hatch success of both species, particularly Shoal Bass. Discharge and temperature conditions explained more variability in daily growth for Shoal Bass compared to Largemouth Bass. My results indicate important species-specific relationships that influence movement patterns and successful hatching and underscore the importance of maintaining components of a natural flow regime. If the goal is to promote recruitment in these populations, then consideration of dam operations and examining the level of angler exploitation during important spawning times may be worth consideration by managers.