Cooperative Fish and Wildlife Research Units Program: Mississippi
Education, Research and Technical Assistance for Managing Our Natural Resources

Populations show temporal and spatial fluctuations in abundance, partly due to random processes and partly due to self-regulatory processes. We evaluated the effects of various external factors on the population numerical abundance of curimba Prochilodus lineatus at five sites of the remnant floodplain of the Upper Paraná River, Brazil, over a 19-year period. Panel data analysis, with the time series of each site as a panel, was applied to examine the structure of temporal and spatial abundance while controlling auto-regressive processes and spatial heterogeneous variances that often obscure relationships. As sources of population variation we considered predation, competition, selected abiotic variables (water pH, temperature, Secchi depth, and specific conductance), construction of a dam upstream of the study area, water level and flood intensity during the spawning period. We found that i) biological interactions (predation and competition) were not significantly related to variations in P. lineatus abundance; ii) specific conductance was a space indicator of abundance, apparently linked to the biology of the species (this variable separated lentic water bodies from rivers); iii) intensity of floods determined inter-annual variation in abundances; and iv) Porto Primavera Reservoir (located upstream from the study area) negatively impacted the abundances at sites in the floodplain directly affected by discharges from the dam. Panel data analysis was a powerful tool to predict changes in fish abundance. Use of this tool identified the need for intense flooding (river levels above 450 cm) to maintain high abundances of P. lineatus and those species with similar life strategy in the upper Paraná River.