Effect of Habitat Fragmentation on Size Spectra of Freshwater Fishes

Habitat fragmentation has been identified as one of the greatest threat in freshwater environments. In the Neotropical region, mainly in Brazil, dam construction is pointed as one of the main cause of aquatic habitat fragmentation. Reservoir construction can result in a restructuration of the aquatic communities, including fish. Many attributes of fish are related to body size. Therefore, size spectrum approaches have been increasingly used as an indicator of aquatic ecosystem structure. In this study, we estimated the size spectrum slopes of fish assemblages at three different reservoirs in Southeastern Brazil, at two different points in time: in the first and in the second year after the reservoirs’ filling. The size spectrum slope, given by the maximum likelihood estimator of the Pareto type I distribution, showed a much steeper size distribution in the first year, implying in relatively higher dominance by small fish, but then showed an increase in slope in the second year towards what we expect are values closer to pre-reservoir conditions. The results also suggested that the fish size distribution can readily track changes in environmental conditions following major perturbations.