Variations in fishing landings from the Itaipu Reservoir: relationships with life history and upstream hydrological regime.

Abstract

Hydroelectric dams are frequently identified as one of the main drivers of biodiversity loss and, consequently, the reduction of ecosystem services. The physical, chemical, and biological modifications caused by damming favor different fish species based on their life-history traits, selecting those with greater plasticity or pre-adaptations to the conditions of impounded habitats. This study investigated the impacts of damming on fishery yields in the Itaipu Reservoir and upstream stretches, based on 32 years of monitoring. It aimed to assess the relationship between the functional traits of fish recorded in landings and the spatial and temporal variation of the studied locations. The results showed that the upstream region had higher abundance in most evaluated traits. This area exhibited high trait similarity with the fluvial region, while the transition zone showed greater similarity with the lacustrine region, indicating that fish landings are influenced by the functional traits of species, which vary over space and time. Changes in the hydrological regime of the Upper Paraná River floodplain were also analyzed before and after the construction of the Porto Primavera hydropower plant, to understand how flood patterns influence the landings of migratory species in the Itaipu Reservoir, considering different temporal intervals. This analysis revealed significant differences in hydrological metrics following the operation of the Porto Primavera Hydropower Plant. Collectively, these findings illustrate the spatial and temporal variability of fish landings in the Itaipu Reservoir and upstream, highlighting the harmful effects of upstream dam operations on the sustainability of fish stocks in the assessed areas. Different flood patterns affect the yields of migratory species, with significant impacts observed between two and four years afterward. Among the main contributions of this thesis is the large-scale integration of data on fishery landings in the Itaipu Reservoir and upstream areas. It was found that the composition of fish landings depends on functional traits, which vary across spatial and temporal scales. A key approach adopted was the use of hydrological descriptors based on the Indicator of Hydrological Alteration index, applied to characterize flood patterns in the floodplain located upstream of the Itaipu Reservoir—an area essential for the spawning and development of migratory species. Furthermore, the effects of different seasonal flood types in this floodplain on fishery yields in the Itaipu Reservoir and upstream were analyzed.